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Quincy

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April is seen as a transition month during the severe weather season, as the frequency of tornadoes typically picks up rather quickly through the month. Despite what the calendar has to say, tornado activity has been fairly lackluster so far this month. In fact, after moving well above the average to-date tornado count in late February, the U.S. has steadily been losing ground. As it stands now, through April 18, the U.S. is near average this year for tornadoes, but with a relatively quiet rest of the week forecast, it looks like the country will fall below average for the first time since February. (The 1986-2015 climate period of 30 years is used for this average)

 

The month of April started with the “dreaded” trough of low pressure across the Northeast. Locally, it was cold and snowy after a winter that was relatively mild and snowless. Likewise, after an active winter season for tornadoes, severe activity has been sporadic over the past several weeks. With all of this said, a pattern change is finally on the not-to-distant horizon, with troughiness returning to the West and the welcomed return to ridging across the Southeast U.S. This pattern will broadly support a more active period of weather across the central states, including an uptick in tornado potential.

 

If we’re keeping track, a pattern change was slated for mid-April a long time ago, back as early as mid-March. That pattern change has been delayed somewhat as pesky troughing across southeastern Canada hangs on and the models display a glaring ridge (positive height) bias. This past week saw a shuffling of the pattern, but an omega block led to a messy setup and only a few isolated tornado reports in parts of the High Plains. The models often have issues handling larger scale pattern changes, but now that such a change is effectively inside of a week, confidence is increasing and the models are getting into good agreement.

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By this weekend, the first in a series of troughs is likely to swing across the western half of the country with some modest ridging to the east. Watch for lee-side cyclogenesis in the central High Plains vicinity between Sunday and Monday. While this is encouraging, the setup is not without flaws. This first trough ejection and evolution of the system is kind of junky (for the lack of a better word) in terms of tornado potential. There’s some instability as early as Saturday progged in the north-central states, but shear is forecast to be lackluster. The similar is the case for Sunday and Monday from the Plains into the Upper Midwest – generally marginal overlays between modest shear and favorable instability as a frontal system slides east. This is subject to change, but the trends are not particularly impressive. It’s the middle and latter portion of next week that really bears watching, figuring that this first system may at least get the gears turning for building a warm, moist air-mass over the Plains.

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With the Euro and GFS in good agreement (including the ensembles), it’s fair to use the GEFS analogs as a baseline for what type of setup we could be looking at, somewhere in the Tuesday to Saturday (April 26-30th) time-frame. Even before looking at specific dates, the string of digging troughs in the West with increasing moisture return in the central states sets the stage for a classic period of near-peak/peak tornado season activity. This does not necessarily mean we will have a massive number of tornadoes or that there will be a high-end setup, but at the very least, it is probable that tornado activity will markedly pick up as the week wears on. Now speaking of those analogs, there are some big dates and periods that show up, in order from ranking:

  1. 5/10/1953: A couple of days removed from the day 6-10 analog, but this date featured a localized outbreak of strong tornadoes in the Upper Midwest.
  2. 4/25 – 4/29/1994: 124 tornadoes in five days, including an outbreak from the 25th into the 26th.
  3. 5/12 – 5/13/1980: Not an outbreak, but strong tornadoes in Missouri followed by a pair of EF-3 tornadoes in Michigan the next day.
  4. 4/17/1995: AR/OK/TX outbreak with 21 tornadoes.
  5. 4/26/1991: Plains outbreak with 53 tornadoes, including the Andover, KS EF-5 tornado.
  6. 5/2/1994: The only analog in this bunch that didn’t have notable tornado activity.
  7. 5/7 – 5/11/2008: 122 tornadoes in five days. (2008 has been an analog on the radar for a while, also one of the busiest spring seasons of this century)
  8. 5/8/1979: 21 tornadoes, though mostly in Florida, two were reported in Iowa, including an EF-3.
  9. 4/30/1978: 15 tornadoes in the southern Plains, including 6 strong tornadoes and a mile-wide EF-4 on the northwest side of Oklahoma City.
  10. 5/4 – 5/6/1960: 71 tornadoes in three days from the Plains into the Midwest, including a long-track EF-5 tornado in eastern Oklahoma.
  11. If the pattern unfolds closely to what is modeled, it would appear that April certainly has the potential to go out with a bang.

 

Through some of the research I’ve done with a May tornado outlook for USTornadoes.com, I noticed that the analogs have things in common. Without giving away too many of the details, one of the common themes in the analog was for the potential for violent tornado events in May. It could be the case that we’re just getting warmed up next week…

Quincy

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A localized threat of severe thunderstorms, including possible tornadoes, targets Arkansas Sunday afternoon into the evening hours. A compact shortwave trough approaches from Oklahoma during the afternoon, with a modestly warm, moist flow from the south to southeast streaming up the lower Mississippi Valley.

 

Computer forecast models have been quite consistent with this general threat for quite some time and now that Sunday is approaching, some high resolution, short-term guidance has been reviewed. Clusters of severe thunderstorms are expected to form during Sunday afternoon and track east to northeast across the region. Large hail and a few tornadoes are expected, along with damaging wind gusts and some localized flooding, mainly where any heavy rain falls over already saturated, or even flooded, areas.

 

With the environment across the Arklatex vicinity being largely undisrupted, a corridor of moderate instability is progged from the Arkansas/Oklahoma border, southeastward across Arkansas and northern Louisiana. The focus for thunderstorm initiation will be immediately head of a weak surface low crossing over from Oklahoma into Arkansas.

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The 4km NAM has been consistent for several runs now, showing discrete cells forming on a northwest to southeast axis from approximately Fort Smith to Malvern and southward into southern Arkansas by mid-afternoon. Given the environment, supercells are likely with large hail being the initial threat, given cold air aloft and relatively steep mid-level lapse rates. By late afternoon, the tornado threat will likely increase due to several factors, including locally backed near-surface winds, an increasing low-level jet and terrain influences.

 

The greatest apparent tornado threat will be from central to east-central Arkansas, given very good model agreement with the most robust cells forming in this location, just ahead of the surface low. There is also a possibility that moisture return may also be slightly underestimated by the models given recent rainfall across the region.

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Nonetheless, the setup may also take advantage of channeling of low level flow in the Arkansas Valley, as has been seen many times in the past, meaning that a tornado or two could also be possible between Conway and Fort Smith, on either side of I-40. The confidence in thunderstorm initiation decreases with southward extent, particularly from far southern Arkansas into northern Louisiana. Although some convection may fire here, the most robust storms are likely to remain farther north.

 

Into the evening, the cells will mature and move northeastward, perhaps reaching the Memphis area before merging/weakening overnight. Both high resolution guidance and the GFS agree in a swath of heavy rain/convection from roughly Little Rock to Memphis. This means that some localized flooding may be possible here. Given the thermodynamic and kinematic environment, a strong tornado cannot be ruled out. Model QPF swaths all support the idea of discrete or semi-discrete convection, particularly from 21-03z from central to eastern Arkansas.

 

One last note is that although models have been in strong agreement, there may be a very slight slowdown of the system, but this will not have major impacts on the outcome. It does mean that a few strong to perhaps severe thunderstorms may fire in eastern Oklahoma early in the event and that the severe threat will decrease with eastward extent, to the east of the Mississippi River.

Quincy

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Multiple variables are important to consider when it comes to supercell thunderstorm development. The Supercell Composite Parameter (SCP) was created to factor three important ingredients to determine how favorable an environment is to produce supercells. SCP focuses on instability, wind shear and helicity (potential for updraft rotation). SCP is a parameter that starts at zero and becomes higher as there is better overlap of parameters to favor the formation of supercells. For example, an SCP of zero suggests that supercells are unlikely to form, while a value of 10 suggests a much better likelihood of supercell formation. There will be more discussion later on as to what SCP values support supercells.

 

Calculating SCP

MUCAPE term * effective bulk shear term * effective SRH term

instability term * wind shear term * helicity term

 

The equation is more specifically

(MUCAPE/1000 J•kg-1) * (EBWD/20 m•s-1) * (ESRH/50 m2s-2)

 

This tells us that each variable has a “threshold” in the equation. Basically, instability of 1000 J•kg-1 will equal out to 1. For bulk shear, 20 m•s-1 (~39 knots) will bring that term to 1. With helicity, 50 m2s-2 is the threshold. (EBWD stands for effective bulk wind difference/shear) Effective shear is used instead of 0-6km shear, for example, since it takes into account storm depth. Effective SRH is used as opposed to standard SRH, as ESRH is tuned to discriminate against environments with considerable capping, that may prevent air from being able to rise and form a thunderstorm.

 

An SCP value of 1 is relatively low and most surface-based supercells form when SCP is between 2 and 11. Values much higher are relatively uncommon, but when they do happen, there is a strong probability of supercell formation, assuming other ingredients come into play, such as forcing, breaching a cap and storm mode. The average value for SCP with supercells ends up being close to 6.

 

There are some other considerations to make. Elevated supercells can and often form with "low" SCP values. In fact, some can form with an SCP value below 1 and the average value for elevated supercells is only about 2. An elevated supercell will form in an environment where there is elevated instability, but there may be a low-level inversion that prevents the supercell from routing itself at the surface. Likewise, marginal supercell structures that may be messy or disorganized, can also form with low SCP values.

 

Also, an SCP value can be extremely high, such as 20+, but if there is no forcing mechanism to trigger thunderstorm initiation, there could easily be no supercells in such an environment. This seems to be most common on hot, summer days where there is extreme instability in place, but only modest wind shear/helicity.

 

Below is an example from 2015 where SCP values were over 30 across parts of Kansas, largely due to extreme instability. However, a lack of forcing delayed supercell initiation for several hours.

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The parameter is also helpful because it will be set to a lower value if, for example, there is considerable instability, but little to no wind shear. As wind shear drops below the ~39 knot threshold, the term falls closer to 0, setting the entire equation to a lower resultant number.

 

In summary, SCP is a helpful parameter to evaluate the favorability for supercell thunderstorm development. It takes into account instability, wind shear and helicity, outputting a larger value where there is the best overlap of supportive ingredients. For surface-based supercells, SCP is generally higher than 1. SCP should always be used in combination with other considerations, as a favorable SCP value may not yield any supercells, if there is nothing to trigger updraft (thunderstorm) formation.

 

Read more here: http://www.spc.noaa.gov/publications/thompson/stp_scp.pdf

Forecast models that show SCP: http://weather.cod.edu/forecast/

Quincy

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A pattern change is soon underway that will leave much of the U.S., especially the eastern two thirds, feeling spring fever. Unlike patterns in recent years, a prevalent ridge of high pressure off or near the East Coast (“Southeast ridge”) will maintain generally at or above average temperatures for the region. The only exception may be parts of the Northeast, where some backdoor cold fronts could keep temperatures cooler. To the west, troughing across the West Coast should help keep a much-needed stormy pattern in place for California and surrounding areas. In the middle is where things can get interesting in terms of severe thunderstorm potential with the possibility for above average tornado activity.

 

After taking a close look at past mid to late March patterns over the last 20 years, two periods can be identified as close analogs to what is forecast to unfold, March in 2006 and 2009. The short and medium range guidance is in agreement that the first springlike setup over the Plains gets going on Sunday and lasts into early next week. Beyond that, the longer range ensembles agree that the basic pattern, one with ridging in the Southeast and troughing over the western third of the country, continues. The Euro weeklies show this right through the end of March, while the 16-day GEFS has this setup solidly through the third week of March.

 

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Without spending too much time on details, both 2006 and 2009 saw a fair amount of tornado activity to the north and west of a “typical” March, where activity is favored over Dixie (Deep South/Gulf Coast). There was a significant early season tornado outbreak from March 9-13, 2006 across the Middle Mississippi Valley and Ozarks, particularly over Missouri. In 2009, activity was not nearly as concentrated, but there were notable tornado events across the Plains and Midwest. Essentially, both years had a relatively active March, but the biggest story was how far north and northwest tornado events took place.

 

Both 2006 and 2009 featured ridging across the Southeast and warmer than average temperatures over much of the central and eastern U.S. This is important for the rest of this month. Aside from the warmth, moisture (think instability) is able to travel farther north, which is often a key limiting factor for severe events in the Plains and Midwest in late winter and often early spring. Assuming the pattern that shows up early next week is repeated through the month, we may have a very active March on our hands.

 

Summary

  • The rest of March may feature persistent Southeast riding and western troughing
  • Above average precipitation is expected in California
  • Warmth is likely from the southern Plains to the Tennessee Valley/Southeast/Mid-Atlantic
  • Above average severe activity is anticipated, overall, nationally
  • The threat exists for multiple tornado events over the southern/central Plains and parts of the Midwest

It is not clear at this point if we will have a significant March outbreak like 2006. Also, there are still some limiting factors for Sunday-Tuesday coming up that may preclude a bigger event. Nonetheless, severe weather, including at least a few tornadoes are anticipated into early this upcoming week. Through mid and late March, expect at least a couple of more severe events, continuing the pace for near to above average tornado activity in the U.S.

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Quincy

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Here is a snowfall map using reports from various sources. Many of the reports came from this forum and the National Weather Service. Only social media reports that passed through quality control were considered. All reports gathered were carefully considered and compared before being included.

 

Spotty light rain impacted portions of Connecticut on February 4th as a frontal boundary slowly advanced east through the area. As the front became nearly stationary near the coast, a wave of low pressure developed over eastern North Carolina early on the 5th. As low pressure organized, colder air filtered in and precipitation changed to snow across Connecticut.

 

The storm system moved swiftly to the northeast, but there were several hours of moderate to heavy snow across parts of southern and eastern New England, as well as Long Island. The heaviest snow in Connecticut was observed from New Haven County, northeastward into interior periods of eastern Connecticut. Some of the hill towns in northeastern Connecticut reported just over a foot of snow. Snow came to an end between late morning and the afternoon hours on the 5th.

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Quincy

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A tornado outbreak appears likely on Tuesday into Tuesday night across portions of Alabama, Mississippi and Tennessee. Over a broad area from the lower Mississippi Valley to the Tennessee and lower Ohio valleys, scattered severe thunderstorms are expected to develop Tuesday afternoon, continuing into Tuesday evening. The threat will shift east overnight, gradually lessening, especially after midnight. The setup looks favorable for several tornadoes, including at least one or two strong tornadoes.

 

Overview: Discrete to semi-discrete thunderstorms are anticipated to develop over central to northern Mississippi and western Alabama as early as midday Tuesday. The severe threat quickly ramps up over Mississippi by early afternoon, although it not be until mid-afternoon that the earliest for a severe threat over western Alabama. (Early convection may be elevated) Other storms are likely to fire into western Tennessee, while a new line of thunderstorms initiates near the Mississippi River during the afternoon. Basically, you have storms right ahead of a cold front (the western line of storms) and warm sector supercells. The supercells in the warm sector have the greatest risk at producing strong, long-tracking tornadoes. I do not see this as a high-end or historic outbreak, but my best estimate at this point is for 8 to 12 tornadoes with at least one or two strong (EF-2+) tornadoes. The other point to make is that the tornado threat will continue after dark across northeastern Mississippi, northwestern Alabama and middle Tennessee. As storms merge and are eventually overtaken by a squall line, the tornado threat should lessen after midnight.

 

The greatest risk for tornadoes is expected to extend from central to northern Mississippi into western and northwestern Alabama, western to middle Tennessee and western Kentucky. Strong tornadoes are most likely to form across northeastern Mississippi and northwestern Alabama into west-central Tennessee. A couple of brief tornadoes cannot be ruled out to the east or even north of this purple area, but the tornado threat is much lower in those locations.

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The models showing greater instability (NAM, SREF, RGEM) are verifying quite well. Given dew-points already into the mid-60s in southwestern Mississippi by 11 p.m. CST Monday and dew-points around 70 in parts of Louisiana, moisture return is going to plan or slightly greater than prior forecasts. The biggest variable affecting the extent of any outbreak tomorrow is instability. It looks like much of northern Mississippi and perhaps western Tennessee will see SBCAPE values of 1000-1500 J/kg by early afternoon. This instability, when coupled with favorable wind shear, would absolutely favor tornadic supercells. The HRRR is trending even greater with instability, but the progs of 1500-2000 J/kg by midday may be a bit overdone. Still, it should be noted that 1000 J/kg is about the average amount of CAPE for cold season tornadoes in Dixie, especially with the magnitude of shear that is expected to be observed later Tuesday.

 

The point is to be prepared for severe weather, including tornadoes, across the areas mentioned above, anytime from Tuesday afternoon onward. There may be some weak shower activity in the morning, but that will most likely not be severe. Trends with any early showers will need to be monitored, as convective/cloud debris could have an affect on destabilization. later in the day.

Quincy

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A tornado threat is still being closely monitored for Tuesday, as computer model forecasts and trends have been fairly consistent with the potential for severe weather on February 2nd for quite some time. There really are no major changes from the previous forecast, but there are still a few question marks that need to be resolved. Some new high resolution model guidance that came out Sunday night suggested that the threat may be leaning towards a higher impact event than a lower impact one.

 

Overview of setup and tornado potential:

  • Low pressure tracks into the Midwest on Tuesday
  • Warm, moist air to the south and southeast
  • Strong wind fields aloft with this system Thunderstorms expected 2nd half of Tuesday
  • A few tornadoes are probable
  • There is a strong, long-track tornado threat
  • Area of focus is still the Lower MS Valley to TN/OH Valley

The purple area shaded below is where tornadoes are most likely on Tuesday. A conditional “wildcard” risk exists from parts of central to southern Mississippi into western Alabama, but confidence is not very high yet in discrete supercells being able to develop in that area.

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PROSFavoring a tornado event: Speed shear is very favorable for tornadoes, with more than 50 knots of 0-3km shear and 30+ knots of 0-1km shear likely. The directional shear is decent, with a southwest flow in the mid and upper levels with winds locally south to south-southeast in the warm sector. A delayed start to convection will likely result in a discrete thunderstorm mode early on. If the warm sector has less convective contamination early in the day, that could also allow instability to bump up a bit from recent forecasts. Moisture return is very solid for February, as 60-65+ degree dew-points are likely across much of Mississippi, Alabama and western Tennessee. A few analogs have consistently showed the potential for a tornado outbreak given the forecast setup. The 21z SREF and 00z NAM/RGEM also looked a bit more impressive than previous model runs.

 

CONSLimiting factors and areas of question: Capping could ultimately delay the start of convective initiation, resulting in sparse thunderstorm activity Tuesday afternoon. It is unclear how many discrete cells will form in the favorable environment and how large of an area that will cover. The upper level and surface pattern is not ideal, as the trough is more negatively tilted than what is optimal for an outbreak and the surface low will already have become occluded by early Tuesday. Near-neutral height falls across central Mississippi to central Alabama would limit the ability of storms to initiate early in the event. Although mid-level lapse rates are favorable near the Mississippi River, they become less impressive with eastward extent, based on most model projections. Any mesoscale boundaries that setup on Tuesday could also be factors. Instability is another issue. Although significant levels of instability are not necessary for a dynamic winter event in Dixie, forecast CAPE for Tuesday still appears to be marginal to modest.

 

Sunday night model data: The 00z 4km NAM was very concerning, showing an extensive line of supercells developing by early Tuesday evening from Mississippi to Kentucky. Although the NAM did not really show any convective initiation to the south across central Mississippi to western Alabama, this the environment in that area will be supportive of tornadoes. It’s just that a lack of forcing and little to no height falls make this a conditional threat. With that said, the 00z RGEM does imply discrete to semi-discrete storm development on both sides of the Mississippi/Alabama border area. The NAM hinted at this, especially with some locally backed winds and elevated severe weather parameters. The GFS did not show any major trends one way or the other, but with its coarse resolution, it is not being used as a primary model of consideration. The SREF has also been gradually trending more impressive with the environment over the region for Tuesday.

 

The analog data has not changed much either, with January 19th, 1988 still being the top analog of choice. “It only takes one,” meaning that even if this event is largely a dud, the environment could easily support a significant, long-tracking tornado. The odds of at least one strong tornado are increased to 70% with this update.

 

Periscope video briefing on this potential eventhttps://www.periscope.tv/w/aX7aEDFsWktwcm1ud29Fbm18MWRqR1hhZFJrcE9KWt2OHgSuGqDHLDJbVuDezoEH2_k4l2FthEZuqXLrLa7J

Quincy

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The threat for severe thunderstorms, including tornadoes, continues for Tuesday. The area of focus is the lower Mississippi Valley into portions of the Tennessee Valley and lower Ohio Valley. Nothing significant has changed from the computer models, suggesting that a severe weather event is still probable Tuesday into Tuesday night with at least a few tornadoes possible. There are still details to nail down, but at least a few key ingredients are in place for tornadoes across the region.

 

Thinking since Friday morning’s update has not really changed. The computer models have gotten into better agreement with timing, as the Euro stopped its westward/slower trend and both the GFS and NAM are similar with the overall timing. There still are big questions about instability, as greater instability than forecast would support a higher-end event. As usual, the GFS and to some extent the Euro show marginal to modest instability, while the NAM (as often is the case) is a bit more robust. Wind shear, both directional and speed, is very favorable for tornadoes and the overall upper level pattern is supportive as well. Backing of low-level winds to the south/south-southeast should be coupled with southwesterly winds in the mid and upper levels. The one notable trend on the models has been for more of an initially discrete mode for convection Tuesday afternoon and early evening. If initiation is delayed, that could allow for further daytime heating, juicing up the setup even more. Also, if the storm mode is more discrete versus a squall line, the tornado threat would be elevated. It appears that the storm mode will eventually trend to a squall line regardless, especially as the shear pattern becomes more unidirectional overnight.

 

Current thoughts: Discrete and semi-discrete thunderstorms fire in far eastern Arkansas and northeastern Louisiana Tuesday afternoon. The storms moved northeast and have the greatest threat of producing tornadoes from near the Mississippi River, northeastward to southwestern Kentucky, western Tennessee, northern Mississippi and northwestern Alabama. Given the expected wind fields, strong, long-tracking tornadoes remain a possibility. Odds for at least one strong tornado are set at 60% with this update.

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A tornado threat exists outside the red shading above, mainly in two areas. One being near the triple point in eastern Missouri to southern Illinois, but meager instability suggests this threat is highly conditional. Also, a few discrete cells could fire in the warm sector farther south in Mississippi (possibly western Alabama), but weak height falls suggest that the best forcing will be farther northwest.

 

Once more high resolution data can be reviewed Sunday night, hopefully more details on the magnitude of this threat can be given with higher confidence. When reviewing analogs of similar setups in the past, most have produced at least some severe weather, but when instability was moderate to strong, such a setup often produced a significant tornado outbreak. At this point, this appears to be a low to moderate tier winter tornado event, not too uncommon for early February. One recent trend that may support a higher-impact event is that surface temperatures on Saturday were much warmer than forecast across much of the Mississippi Valley and Ohio Valley. If this trend were to continue in the coming days, it could allow for more instability than currently forecast on Tuesday, enhancing the tornado threat.

 

To give a rough idea of what this event might look like, below is a reasonable analog from the January 19th, 1988 event. That setup also had lower end instability, especially over western Tennessee. It's not uncommon for winter Dixie events with high shear/low CAPE to produce tornadoes, some strong and long-tracking.

Quincy

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A notable threat of severe thunderstorm activity in early February has been showing up in the models for several days now. As the event gets closer, confidence is increasing that a setup favorable for severe weather is likely to occur. However, there still are a lot of details left to be nailed down. The broad pattern involves a vigorous trough in the jet stream digging across the Four Corners region on Monday, February 1st and swinging east to northeast across the United States into Groundhog Day. The greatest severe weather threat will be focused on where energy around this trough ejects with the orientation (tilt) of the trough being a factor of important consideration.

 

Lee-side cyclogenesis is likely on Monday across the southern High Plains with low pressure rotating from the Texas/Oklahoma vicinity into the Middle Mississippi Valley and eventually the Great Lakes. Given the low-level jet projected with this system, ample moisture return should bring 60+ degree dew-points northward into the Gulf Coast states. Instability forecasts have varied from weak to modest and the shear signal has been significant, with a sizable area of 50+ knots of 0-6km shear likely.

 

Similar setups in the past (analogs) have mixed signals, with some showing significant severe outbreaks and others with little to no severe activity. My main focus at this point is the orientation of the trough. A more negatively tilted trough will yield an increasingly unidirectional wind field. If the trough is closer to a neutral tilt or slightly positive, that would maximize the amount of directional shear. The trends appeared to favor the trough becoming negatively tilted on Tuesday, February 2nd, meaning that the storm mode could get messy and trend toward a squall line. The new 00z ECMWF shows a trough closer to a neutral tilt as the upper level flow is southwesterly, not south-southwesterly. If this were to be a hiccup and the trough is more negatively tilted, then the severe threat will not be maximized. It is important to note that severe thunderstorms, including tornadoes, will still be possible in this scenario, but if the ECMWF is correct, we may have a more significant threat to monitor.

 

Based on the latest data, I would expect an isolated, conditional severe threat to develop across the southern Plains late Monday into the overnight, mainly from parts of North Texas into the eastern half of Oklahoma. Given cold advection and steep mid-level lapse rates, the major threat would likely be large hail, although damaging winds and perhaps a couple of tornadoes would also be possible. Tuesday is the day of focus, as any discrete to semi-discrete thunderstorms that develop in the warm sector could become tornadic. It appears that this area will encompass northeastern Louisiana and eastern Arkansas into Mississippi, far southeastern Missouri, far southwestern Kentucky and western to middle Tennessee. Although the threat could punch north into southern Illinois, southern Indiana and more of Kentucky, meager instability amidst an increasingly pinched warm sector, there is lower confidence in this scenario. Also, the severe threat could reach Alabama later in the day, but the last several runs of the ECMWF have suggested a somewhat slower evolution, keeping the threat a bit farther west, perhaps only reaching northwestern Alabama.

 

With all of this said, severe weather seems likely on Tuesday with at least a few tornadoes. The wind fields would support a strong tornado. If one or a combination of the following conditions are met, then this setup could turn into a higher-impact event with numerous tornadoes, some strong and long-tracking: More instability than currently forecast would support a more robust setup, particularly in terms of localized vs. larger scale. A near-neutral or even slightly positive tilted trough would increase the amount of directional shear. Discrete thunderstorm development in the warm sector, especially early in the day on Tuesday, would suggest an elevated tornado threat.

 

First thoughts:

 

-Conditional threat of a tornado or two late Monday night/early Tuesday.

-At least a few tornadoes on Tuesday; better than 50/50 odds of a strong tornado.

-Tornado threat is maximized on Tuesday from far northeastern Louisiana and eastern Arkansas into northern Mississippi, western to middle Tennessee, far southeastern Missouri, far southwestern Kentucky and northwestern Alabama.

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Quincy

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Here is a snowfall map using reports from various sources. Many of the reports came from this forum and the National Weather Service. Only social media reports that passed through quality control were considered. All reports gathered were carefully considered and compared before being included.

 

Snow reached southern Connecticut during the predawn hours on January 23rd. The snow gradually moved inland, dropping the most persistent bands of moderate to heavy snow on an axis from Fairfield County, northeastward into New Haven County and parts of eastern Connecticut. As low pressure slowly moved east to the south of Long Island, precipitation never reached the far northwest corner of the state.

 

During the peak of the storm, winds consistently gusted to between 30 and 40 mph along the shoreline. No Connecticut stations officially reached blizzard criteria, but near-blizzard conditions affected southwestern Connecticut at times.

 

Breaks in the precipitation shield across southeastern Connecticut resulted in locally lower amounts of snow, particularly across New London County. Snow quickly came to an end in all areas early on January 24th, ending from west to east across the state.

 

The Blizzard of 2016 affected a large portion of the United States from the Arklatex region, eastward to the East Coast. The most intense snowfall fell from the Mid-Atlantic states into the New York City metropolitan area. Snowfall totals of 2 to 3 feet were common here, with a few locally higher amounts. All-time single event snowfall records were set at Allentown, Baltimore, Harrisburg and New York City’s JFK Airport. A record daily snow depth was also set at Washington Dulles International Airport. Both Harrisburg and JFK Airport reported 14 straight hours of snowfall rates of 1 to 3 inches per hour during the height of the storm. JFK Airport observed 30.2 inches of snow in one calendar day on January 23rd.

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Quincy

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For the fourth year in a row, overall severe thunderstorm activity, including tornadoes, finished below average across the Lower 48. This graphic shows the severe thunderstorm watch departure from the 13-year average. The vast majority of the U.S. saw at or below average numbers of severe thunderstorm watches. The greatest departures from average were across the central Plains into parts of the Midwest. The only state with more severe thunderstorm watches than average was Texas, with a higher instance of watches over parts of central to southern Texas. What was the cause for this, aside from the seemingly long-term lack of severe thunderstorm activity?

 

The 2015 severe weather season actually got off to a relatively fast start from late March into early April, remaining active into much of May. Attention shifts toward June, which is usually the the peak of the season. June 2015 featured substantial ridging across the western U.S. While not the sole factor, that ridging was a big player in the relative lack of severe thunderstorm activity into June. The severe season climatologically focuses in to parts of the central and northern Plains in June, but the 500mb height pattern in June 2015 was not the most favorable for severe thunderstorms. Some troughing evident over the Great Lakes favored multiple severe weather events across the Midwest and Ohio Valley. However, even here, the season, overall (not in all cases), was on the quieter side.

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Above image shows 500mb heights and anomalies for June 2015.

The overall tornado activity in 2015 was below average, but some parts of the country did see an increase in activity compared to recent years. Portions of Iowa and northern Illinois saw a very active tornado season. This included an early season outbreak on April 9th and a fall event on November 11th. Texas also saw an active season, particularly in North Texas. The High Plains saw a broad area of increased activity, particularly from the Texas panhandle into eastern Colorado and western Kansas. The other part of this graphic that stands out is the lack of tornado watches across the Deep South. Given recent trends and forecasts, it is conceivable that the severe season over the Gulf Coast states, including Florida, may remain on the active side over the next few weeks. Deeper into the year, it is a bit more unclear if March and April will see an uptick in activity across Dixie Alley. Only time will tell.

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Quincy
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Another vigorous through is forecast to sweep through the south-central states over the next few days, bringing a threat of thunderstorms to the region. Although this threat looks substantially less impressive than the event in mid-November, there still exists the potential for at least a few severe thunderstorms, especially Saturday.

 

The setup for Saturday has had a lot of question marks and red flags from the start, but now that the event is approaching, things are coming into better focus. The upper level pattern is split with a fairly complex setup forecast to develop. It looks like two pieces of energy will factor into the southern Plains severe threat. The first will be a strong daytime low-level jet across eastern Texas with vorticity maxima ejecting north-northeast toward the Ozarks Saturday afternoon. The second area of energy hangs back with a cold front and the more substantial height falls across the southern High Plains.

 

The greatest severe threat, although still somewhat limited, should develop from eastern Texas into perhaps southeastern Oklahoma/far southwestern Arkansas during the afternoon hours on Saturday. Aided by a 40-50 knot low-level jet and modest instability, at least a few supercell thunderstorms could fire. Given the wind profiles, all severe hazards appear possible with perhaps a few tornadoes. The threat here shifts to damaging winds as storms merge and should tend to wind down after dark as daytime heating fades and the strongest forcing moves into the Ozarks and Middle Mississippi Valley.

 

The secondary severe threat looks to be from central to North Texas, into central and western Oklahoma. This could extend into Kansas, but with northward extent, instability will become increasingly limited. There are three issues with this area, with the first being a continued messy look to the wind profile. Model soundings have shown a veer-back profile in the mid-levels, producing some jagged, criss-crossing hodographs. Also, some warmer temperatures in the mid-levels should keep the atmosphere capped in most areas until early in the evening. Finally, the trough has slowed down a bit on the models, which also keeps the best forcing farther west until after dark. The timing is analogous to 11/16/15, but instability is significantly less impressive and shear is not as robust. Although a tornado cannot be ruled out, the threat is fairly low.

 

For this area, thunderstorms will try to develop around or shortly after sunset, but may have trouble organizing given the above-mentioned factors. Still, given cold advection aloft and moderate shear, a few briefly discrete/semi-discrete severe thunderstorms could develop. The most likely scenario is that thunderstorms form into a squall line and feature damaging winds as the main threat overnight.

 

Speaking of mid-November, the Sunday threat has a lot of similarities to 11/17/15. Not only with timing and placement, but with the synoptic setup. Keep in mind that 11/17 had more instability and was an “elevated” 10% tornado threat, but the event struggled, mainly producing sporadic damaging wind gusts, although a few overnight tornadoes were reported in Mississippi. This Sunday, the initial squall line looks to be only marginally organized (unlike the robust 11/17 AM line) and the potential for warm sector supercells out in front, across the Lower Mississippi Valley, is fairly low. Still, a few damaging wind gusts and perhaps a tornado or two appear possible. With the warm sector becoming increasingly narrow (pinched) through the day, the aerial extent of severe threat should fade during the second half of the day, despite impressive wind fields aloft.

Quincy

blog-0601325001438742546.gifA series of supercell thunderstorms moved through central and eastern Massachusetts this afternoon. Some of the storms prompted tornado warnings and there were multiple significant severe weather reports as a result. Some of the thunderstorms originated as far west as eastern New York and later reached peak intensity as they moved into portions of central and southern New England. Even the coastal community of Boston was hit with some regionally impressive severe weather.

The prelude to these afternoon storms actually came in the form of early-day severe storms this morning. A line of severe wind-producing thunderstorms affected portions of southeastern Connecticut, Rhode Island and Cape Cod. An area that does not often see severe weather, especially during the morning hours. Once those storms moved out, there was some clearing, which led to plenty of daytime heating to fuel another round of thunderstorms.

By early afternoon, there was an area of moderate to strong instability developing across the eastern half of Massachusetts, coinciding with seasonably strong wind shear. The mesoanalysis showed a corridor of moderate buoyancy coinciding with more than adequate wind shear for supercell thunderstorms. Bulk wind shear was in excess of 50 knots across the region. With clusters of thunderstorms ongoing across portions of the area, the storm mode was going to be critical in the evolution of the event. If storms merged, lines would form, suggesting more of a damaging wind threat. If the storm mode was messy, the inflow region and overall environment could be disrupted, resulting in mainly sub-severe storms. However, if any storm could remain discrete and from on the southeastern fringe of the activity, in order to take better advantage of stronger instability, then things would become a bit more interesting.

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Two thunderstorms began to split in northern Worcester County shortly before 2 p.m. The northern most storm tracked east-northeast into far southern New Hampshire. This storm merged with surrounding storms and did not strengthen much. The southern storm took a bit of a right turn and continued in a generally eastward direction. This cell moved through northern Worcester County, organizing quickly into a robust supercell. Velocity and hail signatures increased, indicating the likelihood of 1-2″ diameter hail. This storm further organized with rotation becoming more focused. A hook was noted on radar and a Tornado Warning was issued. The storm continued into northern Middlesex County, dropping more large to significant hail, but the velocity signature was marginal at best for tornadic development. The main story was hail.

Speaking of hail, a second supercell developed on in west-central Worcester County a short time later. This storm was semi-discrete, but remained that way for quite some time. It also dropped large hail and continued for two more hours, moving right through downtown Boston. Large hail was reported throughout portions of the city and surrounding areas. Overall, there were numerous reports of golf ball or larger hail across Massachusetts, with at least three confirmed reports of hail at least two inches in diameter. A few additional discrete storms developed later in the afternoon, but earlier storms had overturned the atmosphere a bit. These storms were generally strong to only marginally severe in nature.

No tornadoes have been confirmed as of 10:00 p.m. Although there was some localized backing of low-level wind fields, the lack of favorable low level helicity was a limiting factor in the tornado potential. Nonetheless, a fairly uncommon significant hail event affected the eastern half Massachusetts, an area that based on a 1980-2006 average, only reports significant hail once every 6.75 years. This is based on four reports across all of eastern Massachusetts, during the time. While there were four significant hail reports in that 27 year span, there were three such reports this afternoon alone. Keep in mind that the time of record is relatively short, as reports from 2007 to this year were also not included.

A look at the 2 p.m. mesoanalysis showing 1000-1500+ J/kg MLCAPE and locally backed near-surface winds in the vicinity of the most robust supercells:

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Quincy

blog-0743583001434894171.gifThere is the potential for a regional severe weather event on June 22nd. The threat zone extends from portions of the middle/upper Mississippi Valley into the western Great Lakes. All severe weather hazards are possible and given the nature of the setup, forecast trends are being closely monitored.

As at least two pieces of shortwave energy rotate from the upper Midwest into the Great Lakes on Monday, a surface low is forecast to deepen from Iowa/Minnesota into Wisconsin. Impressive wind fields for this time of the year will combine with strong instability to create an environment favorable for severe weather. As it stands right now, two rounds of storms are expected. The first round would most likely be in the form of a mesoscale convective system (MCS) Monday morning, moving into the Great Lakes by midday and early afternoon. The second round develops in the wake of this activity, at and shortly after peak heating, later in the afternoon.

The setup is a bit complicated and there are reasons to believe that two rounds of mixed intensity are favored over one robust atmospheric punch. The MCS during the first half of the day could pose a threat for primarily damaging winds and isolated hail. Once that system moves out, there should be modest air-mass recovery. The issue is that wind fields in the lower levels begin to veer, causing a more unidirectional shear pattern. This will likely dampen the tornado potential somewhat. Nonetheless, even forecasts on the more conservative end of the spectrum indicate a setup favorable for at least a few tornadoes. The afternoon to early evening threat may feature fairly widespread damaging winds, if storms were to merge into a linear system. Supercells still appear probable and they may extend into the early evening. However, for the reasons listed above, this does not look like an ideal setup for a major severe weather outbreak.

Trends for this event tend to move the surface low a bit quicker, which also speeds up the veering of winds. The best wind fields may also become somewhat displaced to the northeast of stronger instability to the south. The Euro has joined the GFS/NAM in developing strong instability, as earlier it was showing a less unstable setup. The RGEM is also on-board and all of the models are in general agreement in terms of timing and geographic placement.

Wisconsin is the target for the initial MCS on Monday. That system should weaken as it moves into portions of upper and lower Michigan. Later in the day, the target becomes southern Wisconsin and northern Illinois. Portions of lower Michigan and northwestern Indiana may also get in on some action. Damaging winds should be the predominant threat. The stronger cores can produce large hail and a few tornadoes seem probable.

At least one of the following scenarios would need to occur to more fully maximize the tornado threat: First, outflow from the morning MCS could work to set up one or more boundaries to locally enhance a tornado threat. If the MCS decays faster than projected, that could lead to less disruption of the wind field and even stronger instability. A mesoscale low and/or a main low tracking further south into southern Wisconsin (instead of northern sections) may maintain more backing in the lower level wind fields through the threat zone.

It should be noted that even with the projected wind fields, at least a few tornadoes remain likely. Given both a strong low level jet and 0-6km shear in excess of 50 knots, there is at least some potential for strong tornadoes. All of the factors currently forecast likely place Monday into more of a mid-range (SPC moderate risk) severe weather threat, as opposed to a higher-end (SPC high risk) outbreak. Stay tuned to later forecasts to see how the forecast setup evolves.

The NAM forecast below for 21z Monday shows winds veering substantially across Wisconsin and Illinois:

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Quincy

blog-0418332001434727874.gifA severe thunderstorm threat is expected to develop late this afternoon into the evening hours across portions of the northern Plains. The setup includes an area of surface low pressure ejecting from Wyoming toward the Nebraska/South Dakota border late today. At the same time or shortly thereafter, an embedded upper level shortwave swing through the Dakotas. The combination of kinematic support and strong instability will likely result in several severe thunderstorms with all severe weather hazards possible. The severe weather threat may continue well into the night as storms shift east-southeastward.

The computer models are in good agreement with the synoptic setup and even most of the mesoscale details seem fairly clear. The HRRR/NAM/RAP show an area of low pressure moving into east-central Wyoming by late afternoon with isolated thunderstorm development across much of eastern Montana. The initial development is closer to the upper level forcing at the time and in association with a frontal boundary interacting with moderate instability and modest wind shear. Further east, although stronger surface heating/instability are progged, a fairly strong cap should limit convection for most of the afternoon.

Between about 22z and 00z, surface heating looks sufficient to begin breaking the cap. At this time, robust thunderstorm development appears likely across southeastern Montana and far northeastern Wyoming. In the immediate downstream environment, a secondary warm front/differential heating boundary is showing up with the high resolution guidance. As it looks now, that should be draped roughly near the I-90 corridor from far northeastern Wyoming into the western half of South Dakota. It is here that strong instability and increasing wind fields should be very favorable for severe thunderstorms. Any discrete thunderstorms between 23z and 02z near this secondary boundary are expected to have the highest probability to produce tornadoes. The higher end instability scenarios appear overdone, but even the less dramatic GFS shows in excess of 2500 J/kg MLCAPE overlapped with 60 knots of bulk shear through much of western South Dakota.

Given such instability, the initial threats appear to be large to very large hail, followed by isolated tornadoes. A more substantial damaging wind threat likely develops during the evening hours further east. As the low level jet really ramps up and upper level winds increase, the kinematic environment should support a significant MCS, possibly a derecho. The exact placement of this convective system develops on how and where thunderstorms grow upscale. It appears that beginning in northwestern and moving into central South Dakota is where the model consensus stood as of this morning. This is also supported by an intense inflow environment with moderate elevated instability and a vigorous low level jet (in excess of 50-60 knots) ejecting from northern Nebraska into portions of South Dakota. While the convection-allowing models differ slightly with solutions, they all show an elevated threat of fairly widespread damaging winds into early Saturday morning across much of South Dakota.

This is a fairly interesting case, as this portion of the (western) northern High Plains does not have many significant tornado cases dating back to the early 1960s. One of the red flags for tornado development includes storm coverage as a result of capping. Nonetheless, regardless of geographic region, it is possible for a strong tornado to develop given the expected environment. If a strong tornado were to form, this would most likely be in western South Dakota or perhaps far southeastern Montana/far northeastern Wyoming. Compared with climatology, the projected severe weather parameters tonight fall into the high end of prior tornado cases for the region. Although wind fields intensify into the evening hours, a gradual loss of heating and a trend toward storm mergers may also mitigate the threat. The threat of most widespread impact will likely end up being damaging winds, even if a derecho does not form. For what it’s worth, the 09z SREF derecho probabilities are in excess of 50% for a large portion of South Dakota by 06z Saturday. A few severe thunderstorms are also possible across southern North Dakota and a rogue supercell cannot be ruled out in the Nebraska panhandle either.

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Quincy

blog-0240113001434424406.gifAs the calendar passes deeper into June, there is typically a steady drop-off in the frequency of severe weather threats across the U.S. Last year featured a grand finale to the severe weather season with a fairly significant sequence or tornado events across portions of the north-central U.S. from June 16th to 18th. While this year will likely not see quite an intense show as June 2014, there could very well still be some respectable severe activity with tornadoes.

Mid-June of this year has been on the radar, so to speak, for quite some time. While there are still some model differences, it would appear that at least a couple of days between Thursday, June 18th and Sunday, June 21st should feature at least localized severe weather events. Note that there is some isolated potential before June 18th, this article will focus more so on the 18th onward.

gfsCGP_con_mucape_102.gif?resize=300%2C225With it only being the 15th and plenty of time for forecasts to change, it is too soon to get into specifics. There are at least two main ingredients that would appear to favor severe weather, more-so, perhaps, than the U.S. has seen over the past week or so. Strong to possibly extreme instability is projected to be in place. Both the GFS and Euro show sizable areas of of 3000+ J/kg MLCAPE. The upper level flow is shifting toward a more zonal pattern, at least in the larger scale. An increasingly tight height gradient is likely from the central/northern Plains into portions of the Midwest by the end of the week and into the weekend. This is expected to result in a stronger component to the winds in the upper levels. The result is favorable forcing aloft and enhanced wind shear with any shortwave energy that ejects through.

There are always caveats and red flags. While there may be more severe weather ingredients to work with, the overlap of those parameters may be relatively small. For example, while 500mb flow may be in excess of 50 knots for a time during this period, the best instability will almost certainly remain displaced well to the south and east. This in itself should tend to favor a more localized severe weather risk. Nonetheless, the Euro and especially the GFS progs over the past several runs highlight(ed) the period in and around June 18th to 21st. The potential exists for severe weather, possibly significant, including tornadoes somewhere in the region between the northern half of the Plains to the western Great Lakes. At the very least, some high CAPE/low shear setups are likely. The questions will become, how large can the threat zones extend and will some of the more impressive shear overlap with stronger instability?

Take a look at some forecast soundings for this weekend if you want some severe weather eye candy. It is silly to take these progs too seriously at this point, so we will have to wait and see how the forecasts evolve. A broad geographical area is highlighted here and it will not be until the short-term that exact threat zones can be confidently identified. Nonetheless, at least one or two solid chasing days are predicted between Thursday and Sunday. If you are willing to travel or on a chasecation, there is reason to be cautiously optimistic about the storm chase potential coming up.

Quincy

Recapping May: On the heels of a relatively active month for severe weather and tornadoes in April, May 2015 continued the pace. Although the month started slow with no tornadoes for the first two days and only a handful through the 5th, the greatest single day tornado event of 2015 occurred on May 6th. This was actually expected to be proceeded by a much more significant event on the 9th, but the former won out with 59 tornado reports, as the 9th did not fully live up to the hype/potential*.

The first third of May paced at a somewhat above average count of tornadoes. Steady tornado events continued fairly regularly through the middle and latter portion of the month. Although there was no “defining” tornado outbreak after May 10th, there were multiple instances of picturesque tornadoes. While the previous forecast for May hinged on a near-average month, it looks like the period will end up at least slightly above average. The analog May of 1991 turned out to be the best fit among the four analogs from the 1990s. It was also the most active one of those four. The very persistent troughing across the Inter-mountain West to High Plains was well-indicated in both the forecast ensembles and analog data. Long-range forecasts may not always work out that well, but in this case, the verification speaks for itself. Only four days in the month reported no tornadoes, 5/1, 5/2, 5/12 and 5/31**, which includes an 18-day streak of reported tornadoes from the 13th to 30th.

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To quickly touch on the Plains long-term drought, it has been reduced significantly. Consistent bouts of heavy rain and convective activity have eliminated most of the drought area in the central to southern Plains. It now covers just a fraction of an area that it had before. In terms of tornado activity, the moisture transport northward has boosted the storm potential, but in a way, has also hampered the ability to easily storm chase. Without much EML (elevated mixed layer) influence this May and a tendency for storms to congeal into MCSs (mesoscale convective systems), countless tornadoes have been produced by high-precipitation supercells. Many of those tornadoes were rain-wrapped and/or difficult to see. Portions of Oklahoma reported a record-breaking 20 inches of more of rainfall in the month of May this year. A large portion of the southern Plains came in with precipitation anomalies of +8 inches or more for the month. That essentially means an extra two to three months worth of rain fell, if not more. This has caused major flooding in much of the region.

June 1st through 10th: A general continuation of the recent pattern should continue through at least the first week of June. While the month begins with ridging across the southern Plains, the short-range models and global models alike are in strong forecast agreement with the upper level pattern. A trough is progged to dig into the West Coast with ripples of shortwave energy swinging into the central/northern Plains from June 1-3. Even though neither one of those three days appears particularly significant in terms of tornado potential, multiple severe reports, including tornadoes, should occur each day. After that, the parent trough is expected to continue digging and beyond that is where the forecast gets a little bit tricky. When looking back at the ensemble forecasts, the models had a ridge bias and did not really pick up on the trough becoming as amplified as it may. (For example, the most recent run, May 28th, of the Euro Weeklies looks much different for the second half of the first week of June, in comparison to the May 31st Euro ensemble run, which is more amplified) The trough could also become cutoff as some model projections indicate. The current expectation is that the trough axis may be just a little bit too far west to favor an outbreak-type severe setup in the Plains. With that said, whether the trough eventually ejects east to cause a significant event, or rather just a string of steady days (much like April and May of this year), there should be fairly consistent tornado threats through about the 7th or 8th of June. Rounding out the period, whatever is left of negative height anomalies in the West should relax to near climatology.

Verdict: Somewhat above average tornado activity between June 1st and 10th. Fairly consistent bouts of severe weather, including tornadoes, are expected through the first week of June. Much like the previous six to eight weeks, while there may not be a higher-end severe setup on any particular day, tornado reports should be observed on most of these days.

June 11th through 30th: Fighting with climatology and the computer model forecasts, there is only so long that relatively amplified troughing can dominate the pattern across the western half of the U.S. Starting with analog guidance, the results are fairly mixed. The general pattern assessed in the top four analogs (based off of GEFS 8-14 day prog from 00z 5/31 and extending out 20 days) is characterized as featuring ridging across the western U.S. to central/southern Plains and some troughing across the Great Lakes. It sounds a bit like what happened to start 2015. However, the individual four analogs (based on early June 2015 forecasts) diverge greatly in the period 10 to 20 days following. The 1991 analog, which was a strong match to May 2015, continues to show up. That June featured slightly below average tornado counts. Another analog that was also mentioned in the May 2015 tornado forecast is 1990. This one also shows up for the month of June and that particular month was well above average in terms of tornadoes. On the flip side, the other two analogs showed well below average tornado counts. The expected pattern to start June 2015 resembles late June 2006. That June finished fairly quiet and was followed up by one of the quietest months of July on record in terms of tornado activity. The final GEFS-based analog is 2002. That June was even quieter than 2006 and July of that year was also well below average for tornadoes.

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What can be made out of these mixed signals? Based on persistence and trends observed so far this spring, the computer forecast models have generally erred on the side of too much ridging occurring too quickly in a long-range forecast. It is inevitable that ridging will eventually prevail, but that does not entirely shut off the tornado season. In fact, it is very possible, if not probable, that troughing across the Great Lakes and/or Northeast could enhance the threat of severe weather from the Midwest into the Ohio Valley. A northwest flow regime tends to favor tornadoes in that region, especially the Ohio Valley. The expectation with this forecast is that mid-June should feature decent tornado potential, but that late June may not be as active. All four of the analogs above were eventually followed by a sharp drop-off in the tornado season, whether that came in late June or July. Also, one cannot forget June 16-18, 2014, in which an otherwise quiet tornado season become extremely active seemingly out of nowhere.

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Moisture return cannot be overlooked and this sets June 2015 apart from recent months of June. The soil moisture content across much of the Plains is much higher than it has been in at least two to three years. The period from May 1-29, 2015 featured slightly to somewhat above average soil moisture content from the Southwest into most of the Plains. This available moisture alone would tend to favor tornadoes, even if upper air and kinematic support are marginal. If the jet stream can stay active and provide enhanced flow aloft, a setup like mid-June 2014 could be possible sometime in June 2015. If such a setup did occur, available moisture would probably not be a concern at all. The bigger question becomes, can the Plains and Midwest eventually see more EML influence? That may be the difference between another “climo month,” versus a more memorable month for tornadoes.

So far in 2015, it has been an active tornado season in two areas. One lies from north Texas/Red River Valley into central Oklahoma. The other is across the central to southern High Plains. Looking ahead to June 2015, early June features tornado prospects from the central/northern High Plains eastward into the Dakotas and Nebraska. Later in June, signs point toward Siouxland eastward through the Midwest and into portions of the lower Great Lakes/Ohio Valley.

Verdict: Near to slightly average tornado activity between June 11th and 30th.

  • June 1-10 forecast: Somewhat above average tornado counts in the U.S.
  • June 11-20 forecast: Near average tornado counts in the U.S.
  • June 21-30 forecast: Slightly below average tornado counts in the U.S.

June 2015 tornado estimate: 255 tornadoes in the U.S. (slightly above average)

*As has been the case many times this year, morning convective activity and MCS dominance have mitigated the frequency of discrete supercells.

**This is subject to change as it may take a day or two for official reports to come in for May 31st.

Quincy

blog-0803607001431558843.gifThe relatively active month of May looks to heat up again in the coming days. After a lot of severe thunderstorm activity last week, the first few days of this week have been on the quieter side. I am looking ahead to three days in particular for the next notable severe weather threats.

Sleeper Thursday: This day has not been on the radar for most, but offers some potential, even if it is lower-end and in a relatively small area. I am focused on western Texas for isolated supercell/severe potential late Thursday afternoon into the evening hours. A small perturbation/vorticity lobe is modeled to pivot from eastern New Mexico into western Texas late Thursday. At the surface, modest daytime heating will likely result in an area of 1000-2000 J/kg SBCAPE, coupled with approximately 30 knots of 0-6km shear. Although the shear is somewhat marginal for supercell potential and the aerial extent of overlapping parameters is small, the higher resolution models do favor clusters of storms developing in this area.

Some red flags include weaker winds aloft and storm mode/coverage, but an increasing low-level jet and backing winds around 00z may provide a small window for tornado development. What gets my attention about this event is that it is under the radar and in favorable chase terrain. I do not expect a lot of people to be out and the High Plains have featured several beautiful structure and tornado events this season, so I am not sure I can pass it up. Worst case, I would bail and head north, to get into closer position for Friday.

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Localized outbreak on Friday:

The model guidance continues to show a strong signal for a severe weather on Friday, with an increased tornado potential across portions of the central Plains. Due to the models speeding up the system just a bit, more forcing and a favorably placed, developing surface low, Friday will probably feature the greatest potential in the otherwise multi-day threat. With the surface low moving into the central High Plains Friday afternoon, the models show strong instability developing across Kansas and Nebraska. The focus appears to be Nebraska, where multiple boundaries/fronts will locally enhance a tornado threat. The warm front is an obvious focus point, as it lifts through Nebraska late in the day. Moving toward late afternoon, the 4km NAM fires a line of discrete storms along a dryline, which will advance eastward through Nebraska and adjacent Kansas ahead of the developing surface low. Look for severe storms along this line, with an isolated to scattered tornado threat. This may extend as far south as sections of north-central Kansas. Along the warm front, the focus narrows in closer to the surface low and warm front/dryline intersection. I would watch the first or second cell closest to that point for a tornado threat. Aside from at least 2000-3000 J/kg SBCAPE (NAM is more like 3000-4000 J/kg), 35-45 knots of 0-6km shear (a bit higher via NAM) and favorable forcing for ascent all favor this severe threat. I imagine that the threat level will be upgraded to Moderate Risk by the Storm Prediction Center (SPC). What makes the threat here a bit more robust than some previous days is that we are not seeing a strong signal of convective debris or MCS activity overturning the atmosphere prior to peak heat. If there should be any convection in the morning, it would likely be limited in coverage, and outflow from that activity may only serve to further enhance the threat by leaving additional boundaries in place. Another quick note is that depending on how wrapped up the surface low becomes, the threat may punch northward into southern portions of South Dakota, especially into Friday evening.

It is hard to really outline any significant red flags for Friday. There is the question of storm coverage, but a higher-end event in this case is actually favored when storms are more isolated. Precipitable water values are also expected to be lower than some recent events, so that further mitigated an MCS threat. I suppose there could be storm mergers and some messy storm mode eventually, but all in all, I think this is a bonafide threat and certainly a day to get out and chase.

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Messy mayhem on Saturday:

The setup, overall, has a lot of similarities to last Saturday. It is likely that some junk convection and MCS activity in the morning will mitigate the threat. Also, the mid to upper level flow looks rather southerly, which is not ideal, as forecast soundings show veer-back-veer issues. With that said, if there are pockets of moderate instability, as the models indicate, there should still be corridors of an enhanced severe threat. This includes tornadoes, as 0-6km shear looks to be at least 40-50 knots and probably higher across some western areas of the threat zone. The red flags win out here, but there is time for this to change. In terms of chase potential, it will take some patience and strategy. Even last Saturday did result in clusters of tornadoes. With this threat being furthest out and potentially disappointing, I will not spend too much time focusing on it at this point. Of course, trends will be monitored and the threat will continued to be monitored.

Quincy

blog-0929003001430859304.gifAs the pattern over North America shifts, an extended period of potential severe thunderstorms targets the central U.S. Although this update covers May 6-10, thunderstorms are ongoing today (May 5th) and were prevalent in prior days as well. The difference here is that we are gradually starting to see more and more potentially potent setups on the horizon.

Wednesday, May 6th: This day has been on the radar for a while and things are coming into somewhat better focus. As shortwave energy pivots from the High Plains to central/northern Plains on Wednesday, an area of surface low pressure will develop. With more forcing in place than prior days, that alone signals an enhanced severe weather threat.

By Wednesday afternoon, a portion of the surface low should be crossing over from far eastern Colorado into western Kansas. The strongest forcing should reside from northwestern Oklahoma into central Kansas. However, the greatest instability will likely be displaced further south from central Oklahoma down into north Texas.

blogentry-533-0-04761000-1430859238_thumPartial to considerable cloud-cover will tend to limit the amount of destabilization that takes place. That combined with modest flow at 500mb, progged to be on the order of about 35 to 45 knots, will tend to limit the extent of the severe weather potential. The surface low itself is also a bit elongated. If it were more concentrated and also deeper, that would signal a greater severe thunderstorm potential. Nonetheless, with a tongue of 1,000 to 2,000+ J/kg CAPE, favorable speed and directional shear, and some forcing aloft should favor at least scattered severe thunderstorms by mid to late afternoon.

In terms of severe threats and the areas to watch…

It comes down to northwestern Oklahoma into central Kansas for what should be the greatest severe threat. More isolated severe storms are still possible along a dryline down into western and central Texas. Large hail, perhaps very large in a couple of storms, appears to be the most significant risk. Damaging winds will be possible, especially into the overnight as storms may tend to merge into lines. There is a tornado threat, which should be maximized during the early evening hours, as the low level jet ramps up. As has been the case many times this year, while there is an evident tornado threat, the intensity and duration of any tornadic storms will be dampened somewhat by the limiting factors mentioned above. There is a fairly good likliehood that multiple tornadoes (but not a major outbreak) will be reported late Wednesday afternoon into Wednesday evening.

Thursday into Friday, May 7th and 8th, also provide some severe weather threat, but in a more isolated and sporadic nature. Upper level heights should remain fairly neutral through the period with no significant forcing noted in the models. Each day is likely to feature moderate instability and at least marginally supportive wind shear for supercell thunderstorms. The corridor for this period should be narrowed in on the Texas panhandle, portions of interior Texas and into Oklahoma. While some severe threat may nudge into portions of Kansas, the greatest (still somewhat limited) threat should hang back further south. Each day, storms may produce large hail with some damaging winds and a few tornadoes.

Each day, watch for a few things: First, where is the greatest instability? If cloud-cover and convective debris are limited during the morning, expect a somewhat enhanced severe weather threat during the afternoon. Also, look for any outflow or other mesoscale boundaries that can be the focal point(s) for storm development. Finally, notice any upper level perturbations, even if seemingly minor, as they could provide just enough forcing to locally increase the severe threat.

blogentry-533-0-66103600-1430859285_thumSaturday, May 9th has the potential, but the keyword is potential, to be a significant severe weather outbreak with numerous tornadoes. The overall pattern is favorable, as a trough swinging from the Four Corners region to eastern Colorado/New Mexico by late-day will provide ample forcing from the High Plains into portions of the central to southern Plains. Caution must be applied when looking at the analogs, but there is a fairly strong signal from the analogs that favors widespread severe thunderstorms and at least isolated significant severe events, including strong and/or long-track tornadoes.

Now, even though some major events show up in the analogs, there are a few limiting factors that will not favor a high-end outbreak. While the flow and forcing increase aloft, 70-80 knots at 300mb and 50-60 knots at 500mb will fall well short of an event such as 4/14/12, which showed up as a GFS-based analog. As far as instability, even though moderate CAPE values are predicted, we’re not looking at strong to extreme instability. There seems to be a common theme, with this week especially, that the atmosphere is not quite taking full advantage, resulting in a less extreme “than possible” setup.

With all of this said, even if the timing is not exactly right, and the timing looks pretty favorable right now, severe thunderstorms are strongly favored on Saturday. What will be the difference between a low-end event and a more significant outbreak will come down to mesoscale details. What also favors severe weather on Saturday is how the models, overall, have been in very good agreement with the general setup on Saturday for quite some time. The focus on Saturday ranges from north Texas through much of Oklahoma and Kansas, to perhaps as far north as portions of Nebraska. All severe weather modes are anticipated, with an enhanced risk of tornadoes.

Sunday, May 10th is a bit further out there, but yet another severe day is quite possible. Details are a bit more muddled, as the evolution of Saturday will have a sizeable impact on what transpires on Sunday. The threat zone inches somewhat east, ranging from portions of Texas up through central and eastern Oklahoma, eastern Kansas and perhaps into portions of Missouri and Arkansas.

In summary, expect severe weather threats for the rest of this week and likely through most of this weekend across the central U.S. At least a few severe thunderstorms are expected each day, with scattered severe storms on Wednesday and perhaps a mode widespread and significant event on Saturday. Tornadoes are possible each day, but the day with the likelihood for the most tornadoes is also Saturday. In terms of storm chasing, there should be many quality opportunities to get out in prime real estate, from the High Plains into the Plains west of I-35. With the threats covering a long period over some similar areas, it may be worth while to hunker down and start thinking of possible targets or even just places to stay (if you’re planning a multi-day trip). Without giving too much away, and since details may change, I tend to favor a corridor from the Texas panhandle into southwest and central Kansas. Climatology also favors this zone for the greatest severe weather threat and trends this year have kept the dryline a bit further west, mainly across these areas, during most events.

Quincy

blog-0445551001430540587.pngThe final few days of April finished on the quiet side in terms of severe and that continued into May 1st. With that said, a larger-scale pattern change is likely to be accompanied by multiple threats of severe weather in the coming days.

Saturday 5/2: Not seeing anything major here. Although we should finally see some modest instability up into the central Plains, dew-points are only expected to rise into the upper 40s to lower 50s across the area with some weak forcing during the evening. One plus is that wind shear will be supportive of supercell structures, assuming other variables line up.

  • Verdict: A few, rogue severe thunderstorms are possible from late afternoon into the evening, but even those may only be marginally severe. The focus is on the central Plains

Sunday 5/3: The setup looks slightly better than Saturday, but that does not say much. A larger area can expect modest to moderate instability, but the drawback here is near-neutral height tendencies. Upper level progs show little focused area of forcing. The only thing that looks somewhat interesting is a surface low forming near the Colorado/Kansas border. This could narrow the focus on some isolated severe thunderstorms to the Texas and Oklahoma panhandles, but even here the prospects are not terribly exciting. If there is enough of a trigger, a few isolated strong to severe storms could also initiate up into the central Plains and as far east as the upper Midwest. Wind shear is questionable throughout the regions outlined.

  • Verdict: Isolated severe thunderstorms are possible anywhere from the southern High Plains into the central Plains and upper Midwest. If there is one area to focus in on, it might be just ahead of a surface low, in the vicinity of the Texas/Oklahoma panhandles. While the ceiling may be somewhat higher than Saturday, storm coverage and intensity is not expected to be particularly impressive.

Monday 5/4: This looks like the beginning of what may be an extended period of active weather. A trough should begin digging into the West Coast, with some modest height falls reaching the High Plains. Moisture will likely be a positive and negative thing here. Although dew-points should reach the upper 50s to lower 60s at a minimum, cloud-cover, convective debris and increasing precipitable water values throw a wrench in the severe storm potential. Likewise, wind shear is not expected to be terribly impressive either. What may end up ultimately happening is that a few pockets of greater instability could lead to a few supercells reaching severe limits.

  • Verdict: Mixed signals somewhat hamper the severe potential, but it would appear probable that at least a few isolated to widely scattered severe thunderstorms could develop from the Texas/Oklahoma panhandles into Kansas.

Tuesday 5/5 through Thursday 5/7: The Euro and GFS are actually in very good agreement overall through the period with the general pattern. The West Coast trough continues to dig and a piece of energy swings through from the High Plains on Tuesday into the central Plains on Wednesday. Tuesday looks muddled at best with meager instability and limited kinematic support. Wednesday may offer the best potential, if things line up. Shortwave energy should be pivoting into the central Plains, along with a surface low, but that low looks awfully elongated. The instability setup may suffer too, from limited instability and on-going clouds/sub-severe storms. With that said, a low level-jet should be cranking with both the Euro and GFS suggesting at least 40-50+ knot winds at 850mb. Thursday becomes a bit more unclear, despite continued model agreement. Storms may be ongoing Thursday morning, based on current trends, and the models seem, perhaps, a bit overdone with instability in the warm sector. Even so, wind shear looks to slacken off, which could be another factor to limit the severe threat. Timing is yet another concern, as a faster evolution could really hinder the Thursday risk, whereas a slower scenario might be better.

  • Verdict: Some isolated to scattered severe thunderstorm potential each day, but details are still unclear. Wednesday may offer the greatest potential with Thursday being a wild card.

The worst case is that this upcoming week, there are just a few severe thunderstorms, but enough of a threat to track for a few days in a row. The best case is that things come together for one to possibly two decent chase days.

Quincy

blog-0980240001430439899.pngThe April tornado forecast was a trial run and a lot has been learned since it was made. After some success with that forecast, I will be incorporating a lot more statistical analysis (analog data) into coming up with a forecast for the month of May.

Quickly recapping April:

Overall, April was a fairly steady month for tornado reports across the U.S., with 21 out of 30 days reporting tornadoes. April 1-9 was very active, including a notable, early season EF-4 tornado in northern Illinois. April 10-18 was relatively inactive, but had tornadoes reported in all but two of those days. April 19-27 was rather active, but no single day featured a major or significant outbreak. Most of the tornadoes in the month were EF-1 or weaker, although the April 9th EF-4 was an exception. Preliminary tornado counts indicate that the month was near to slightly below average in tornado activity. The prior forecast issued on March 31st predicted slightly above average tornado counts. Once the numbers become official, I will get into more detail with comparing the forecast vs. actual.

crh_drought.png?resize=300%2C225Before we get into May, there are some things to consider with the current state of the U.S. Although a long-term drought continues for much of the Plains, heavy rainfall throughout April reduced drought conditions considerably across portions of Oklahoma and Texas. This is critical, because relative tornado inactivity during the first half of spring 2014 across the Plains was at least partially attributed to a lack of available moisture. When we think about creating environments that support tornadoes, moisture is key and that moisture source can originate in Texas. Yes, the Gulf of Mexico is another player, but that moisture must also be able to track hundreds of miles inland, across the big state of Texas.

Additionally, the overall atmospheric pattern has shifted somewhat, as although there has been continued troughiness across eastern Canada and the Northeast, we are seeing a trend toward more ridging developing. This will have many implications on how the tornado season evolves into May. With less blocking across northeast Canada toward the North Pole, that should tend to favor positive height tendencies as well. (Not to mention seasonality helps with that as well)

For this outlook, the focus will be split into two portions. May 1-10 and May 11-31. I will still include breaking the month down into thirds at the end of the outlook, but keep in mind that specifics beyond May 10th lack the confidence needed to get into extreme detail in that time period. May is also a potentially volatile month, as one outbreak or even one day for tornadoes can effectively skew the big picture. It would be difficult to nearly impossible to predict any such outbreak more than 10 days in advance. The point of this outlook is to look at May as a whole.

May 1st through 10th:

After a quiet finish to the tornado season in April, the first few days of May look to continue that theme. This should not last long, though, as both the operational and ensemble forecast models are in strong agreement with the expected pattern. On paper, it looks encouraging for severe weather prospects. An upper level trough and surface low should exit the New England area may May 3rd, leaving the Lower 48 with a relatively zonal pattern, at least for a short-time. Downstream ridging across the East should give way to a digging trough across the West Coast by May 4th to 5th. With some blocking across eastern Canada, we are looking at western U.S. trough that will persist for several days, with potentially multiple impulses rotating around from the Intermountain West into the Plains.

day810.png?resize=620%2C331This could ultimately evolve in many ways. At this point, the most probable scenario would appear to be two to three, perhaps four, days that are conducive for minor to moderate severe weather events, including tornadoes. I would not want to write off the potential for a big event just yet, but it seems more likely that we will have a series of smaller events, kind of how April panned out. What will be working in the favor of severe weather will be the bonus of a better moisture source across the southern Plains and moderate to strong instability ahead of approaching shortwaves. It is the details that get somewhat muddled out, with the amount of clearing/destablization, storm mode, locally backed winds, etc. Essentially, the pattern looks favorable for severe weather and tornadoes, particularly between May 5th and 8th. As mentioned before, maybe only two of those days wind up decent for severe, but if the pattern lines up just right, there could be multiple tornadoes each day.

Verdict: Near average tornado activity between May 1st and 10th. The period should begin quiet, but then see multiple days with at least modest tornado activity. The period may close out with a couple of quiet days as the pattern trends more zonal, assuming the model projections are correct.

May 11st through 31st:

I have put a lot of time into assessing analog data for this period and not so heavily relying upon forecast model ensembles, as was the case with the April tornado outlook. What has been most alarming lately is that the longer-range models have really struggled beyond day 10 over the past several weeks and have often showed little to no skill in the period of days 15 to 30. This means that the models have flip-flopped back and forth, giving little meaningful insight to what might lie ahead. Now, I am not totally discounting the models here. Sometimes they can struggle during a large scale pattern change, much like what we may be seeing into May. I put a fair amount of stock into the European ensembles/weeklies, but I think taking a look at the past will help shed some light on what might happen in the future.

top5_day1-20.png?resize=300%2C232To come up with analogs, I have looked at two things in particular. First, I assessed the short-term model analogs for May 1-2. Secondly, I looked at the day 6-10 ensemble predictions from the GEFS and those analogs. There was some overlap and plenty of similarities to note. In the broad scheme, the analogs began with the western troughing/eastern ridging that we are expecting to see into the first week of May. The analogs are then in strong agreement with positive height anomalies along and east of the Rockies from the 2nd week of May, pretty much through the entire month. After gaining visibility to the latest 00/30 Euro Weeklies, pretty much the same is the case here. That only increases confidence in this forecast. I pretty much disregarded the CFS entirely for this outlook, as its members are all over the place for May and as an ensemble system, has not had a good track record as of late.

top5_day1-20_mean.png?resize=300%2C232Going back to the ridge axis, that is the key thing to consider. The indications, in general, point toward a mean ridge axis setting up somewhere between the Missouri River and the Mississippi River. The latter, or a further east ridge axis, would be more supportive of tornadoes, allowing for troughs to dig a bit further south and west into the Plains. Even the former would be encouraging, as it would tend to favor High Plains activity. That region has not had a great chase season in a while. Based on the reports, it appears as if 2010 was the last solid year there and 2008 was decent too, particularly across western Kansas. Either way, since we are looking at a broad period here and kind of splitting hairs, there is nothing necessarily stopping from a rogue, deep trough to swing through, although it would appear that if that was going to happen, it would tend to favor late May over mid-May. As a result, I am leaning toward a somewhat more active end to May, even though I do expect a fair amount of activity in the middle of the month as well. (When I say fair amount of activity, I expect several days with scattered severe reports, again, in some ways similar to what April featured)

Verdict: Near average tornado activity between May 11th and 31st. The middle of May holds some potential, but is forecast to feature slightly below average tornado reports. Into late May, there are some indications that tornado activity could rebound to near to slightly above average levels with more potential activity.

When looking at some of the recent analogs (over the past 25 years), 3 out of 4 had slightly to moderately below average tornado counts in May. On the flip side, they tended to favor average to even very active months of June. Since May 2015 does not appear to be a particularly close match to any of those analogs, I would take that information with a grain of salt. If anything, it does give at least some additional confidence in the thinking that May could end more active and lead into another active June. I do not want to get ahead of myself here, so we will hold off on further discussion about June until the next monthly tornado forecast.

  • May 1-10 forecast: Near average tornado counts in the U.S.
  • May 11-20 forecast: Slightly below average tornado counts in the U.S.
  • May 21-31 forecast: Near to slightly above average tornado counts in the U.S.

May 2015 tornado estimate: 260 tornadoes in the U.S. (near to slightly below average)

For those wondering, the top 5 analogs are as follows, beginning with the given date and extending out 20 days: 4/28/1994, 5/12/1991, 4/28/1957, 5/10/1993 and 5/18/1977, in that order. The “recent” analogs mentioned earlier in the post were 1990, 1991, 1993 and 1994.

Quincy

blog-0284589001428285045.pngOver a 50-year span from 1962 to 2011, the most violent (F/EF-4 and F/EF-5) tornadoes occurred over Oklahoma and Mississippi. The maximum grid-points reported 16 over that period, with two of those grid-points in central Oklahoma and one in central Mississippi.

While a broad area from the Plains to the mid-South sees the most tornadoes overall across the United States, there are three sub-areas with the most violent tornadoes. Much of Oklahoma falls into that category, as it is widely considered to be in the heart of tornado alley. Further north into Iowa is another area that has seen the most violent tornadoes during the period. The third area falls across Mississippi, where the tornado season is relatively elongated from the heart of winter into mid-Spring. The tornado season in Oklahoma generally occurs in a narrower window in mid-Spring. The season in Iowa tends to fall from mid to late spring with a secondary peak in the fall. A smaller and less significant maximum for violent tornadoes can also be identified across the upper Ohio Valley. While the tornado season tends to peak there in mid-Spring, a few events have also occurred in the fall.

An interesting tornado minimum occurs in a small portion of central Missouri. Among multiple factors is the unique geographical area Missouri falls into. The classic tornado setup in the Plains is driven largely by lee-side cyclogenesis and the dryline. As storm systems move across the Plains, the bulk of the violent tornadoes tend to occur west and northwest of Missouri. Also, the dryline tends to have trouble advancing enough east to penetrate far into Missouri. Likewise, typical tornado events in the mid-South tend to thrive off of moisture from the Gulf of Mexico, producing tornadoes east of Missouri. With that said, higher instances of violent tornadoes have been noted across northwestern Missouri (tornado alley), far southeastern portions of the state (Dixie alley) and the devestating EF-5 tornado in Joplin, in far southwestern Missouri in 2011.

East of the Appalachians, violent tornadoes are fairly uncommon. However, two particular regions have reported three or more violent tornadoes from 1962 to 2011. Portions of the Carolinas fall into that category. Further north, grid-points in the mid-Hudson Valley into southwestern New England have reported four violent tornadoes in that same span.

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Quincy

blog-0276640001427069186.pngHere is a snowfall map using reports from various sources. Many of the reports came from this forum and the National Weather Service. Only social media reports that passed through quality control were considered. All reports gathered were carefully considered and compared before being included.

Snow developed during the afternoon on March 20th across Connecticut. Dry air in place prior to the event resulted in several hours of virga until ground observations finally reported snow early in the afternoon. Snow overspread the state, but the snow was heaviest across southwestern sections. The snow continued overnight as low pressure developed east of New Jersey.

Periods of light snow continued into the morning hours on March 21st. There was some enhancement of the snow across central Connecticut before the snow tapered to flurries statewide by midday.

Snowfall totals ranged from 4 to 7 inches across southwestern Connecticut to just under 2 inches in northeastern Connecticut. Much of interior Connecticut reported 2 to 4 inches with a few isolated higher amounts in north-central portions of the state. A narrow band across the higher elevations of Fairfield County, just northwest of the Merritt Parkway, reported locally 7 to roughly 8 inches of snow.

blogentry-533-0-23414300-1427069173_thum

Quincy

blog-0082077001425438982.jpgHere is a snowfall map using reports from various sources. Many of the reports came from this forum and the National Weather Service. Only social media reports that passed through quality control were considered. All reports gathered were carefully considered and compared before being included.

Periods of light snow developed across Connecticut between late morning and early afternoon on March 1st. The snow became moderate to briefly heavy at times during the evening hours.

Snow tapered off across northwestern Connecticut by midnight, but lingered in eastern areas until the pre-dawn hours on March 2nd. The heaviest snow affected the I-95 corridor and a bit further north into eastern Connecticut.

This event resulted in a general 3 to 6 inch snowfall around the state. The lowest amounts were reported in far northwestern Connecticut with near or just under 3 inches. A few spots in the southeastern half of Connecticut saw 6 to 7 inches of snow.

blogentry-533-0-72122200-1425438947_thum

Quincy

blog-0031519001424701884.pngHere is a snowfall map using reports from various sources. Many of the reports came from this forum and the National Weather Service. Only social media reports that passed through quality control were considered. All reports gathered were carefully considered and compared before being included.

Areas of weak low pressure moved through the Ohio Valley along a frontal boundary on February 21st and periods of light snow moved into Connecticut during the afternoon. The snow gradually became moderate to briefly heavy at times during the evening.

Due to the frontal boundary being west of the state, winds were generally out of the south to southwest ahead of low pressure, through the event. This led to temperatures rising into the lower 30s overnight. Snow changed to sleet, roughly as far northwest as I-84. A narrow corridor of freezing rain was reported just to the northwest of I-95. Some areas changed to plain rain south and east of I-95 along the coast and east of I-395 in far eastern Connecticut.

Precipitation changed back to snow in all areas before ending on the morning of the 22nd.

Most of the state reported a 4 to 8 inch snowfall. A few totals just over 8 inches were reported in Litchfield and Tolland counties. Snowfall totals along and southeast of the I-395 to I-95 corridor were generally in the range of 2 to 4 inches. The immediate shoreline in southeastern Connecticut reported around or just under 2 inches.

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