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Quincy

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  1. Quincy
    I expect mostly snow for just about all of southern New England (pictured on this map). Although there may be a brief mixture along the I-95 corridor in Conn./RI, I expect crashing temperatures and heights to bring a wind-driven snow right down to the coast and into eastern Long Island.
    As far as snowfall totals go, I think that higher ratios will help push NW Conn. and W Mass. to 20"+. Further east, heavy precipitation will offset somewhat lower ratios for 20"+ from IJD to BOS. There is still some uncertainty with areas further south on this map, such as NYC, BDR, GON...lower ratios and possible mixing don't give me enough confidence to go with higher snowfall amounts. With that said, I could see a scenario where even the Conn. coast gets 20". The Euro is basically a 15-25"+ event region-wide and this model has been outstanding with overall consistency in this forecast.
    Bands of heavy snow are expected to form and some orographic enhancement may bring this heavy snow right back into the higher terrain of western Conn. and the Berkshires. A snow-shadow effect may limit totals somewhat in the Conn. River Valley, but even there I think totals will come close to 20". Potential exists for 2+ feet, especially across central and eastern Massachusetts.
    The other story is the strong winds and power outages are a real concern along and SE of I-95. I think drier snow and somewhat lighter winds inland will limit power issues there.
    What really captures my interest here is that expansive moisture field aloft. Past storms, like Feb. 2006, for example, had a relatively narrow area of moisture. This was able to produce intense banding and 20-30" totals from NYC into W Conn. However, with this storm, the moisture field backs into most of NY and covers just about all of New England. The end result is several bands of heavy snow, perhaps even a "mega" band. Snowfall rates of 2-3" per hour will be likely for several hours and convection/isolated thunder is possible.
    Winds may gust to 50 MPH along and NW of I-95, with higher gusts to the east. I think we'll see many stations verify official blizzard conditions and Cape Cod/Islands could see hurricane force wind gusts.
  2. Quincy
    Generally light snow overspread Connecticut from west to east during the morning on January 28th. Snow continued into the early afternoon and at the same time, warmer air moved in aloft. A change to sleet and freezing rain occurred from southwest to northeast, with portions of the I-95 corridor changing over to plain rain.
    Precipitation tapered off to intermittent drizzle with freezing drizzle across much of the interior by early evening.
    Snowfall totals were fairly uniform with most areas picking up 1 to 2 inches. The I-95 to I-395 corridor and points southeast generally received less than 1 inch of snow. A quicker changeover in lower Fairfield County may have also led to slightly lower snowfall amounts. Some of the hilly terrain of northwestern Connecticut picked up a little more than 2 inches of snow.
    I usually do color contoured maps as well, but I'm not sure it's really necessary for a relatively minor event.
    If you have any totals to add or ones that don't match up, please let me know. Sources include this forum, the National Weather Service, social media reports, WXedge.com, the Conn. Dept. of Transportation and CoCoRaHS.
  3. Quincy
    Here are some snowfall maps that I created 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. Blowing and drifting snow made it difficult to obtain an accurate measurement. Some towns had multiple reports and totals that appeared to be too high based off of surrounding reports were not used.
    Some warm-advection snow lifted into Connecticut as early as the night of January 1st, the vast majority of the accumulating snow began on January 2nd. From morning through afternoon, flurries and periods of light snow moved from south to north across the state. By afternoon, some areas, mainly across the northern half of the state, reported an inch or two of snowfall. The 12z sounding from January 2nd at OKX indicated somewhat of a dry layer aloft, while ALY was more saturated. The best snows early on were measured from central New York into portions of interior Massachusetts.
    During the evening, low pressure eventually developed off of the mid-Atlantic coast and an area of snow filled in across Connecticut. It was from about 9 p.m. to 4 a.m. that the heaviest snow fell. The bands of heaviest snow wound up remaining south of Connecticut and there were even more impressive snowfall totals across eastern Massachusetts. There, ocean-enhancement was a key role in significantly higher snowfall amounts.
    In Connecticut, accumulating snow ended by mid-morning on January 3rd, with most areas receiving anywhere from 4 to 7 inches of snow. There was a narrow band of 7 to 7.5 inches across the northern part of the state, where additional snow during the beginning of the event increased overall totals. Close to the coast, there were also a few totals of 7 to 7.5 inches, where some towns were grazed by heavier snow toward the end of the event.
    While there were a few snowfall totals reported in the range of 8 to 9+ inches, those did not line up with other totals in the same or neighboring towns. Strong winds caused blowing and drifting snow, which was the most likely cause for the totals that were assumed to be erroneously high.
    One variable that was generally missed by the computer forecast models was lower liquid-to-snow ratios. While these ratios are generally close to 10:1, model forecasts predicted anywhere from 15-20:1 ratios, or even higher. If higher ratios had been observed, snowfall totals across Connecticut would have been higher. In the end, ratios were fairly close to 10:1.
    It was quite cold during the storm with temperatures falling into the lower 10s and single digits by the morning of January 3rd. Although there is a loose correlation between surface temperatures and snow ratios (colder yielding higher ratios), it was the snow growth above the surface that did not promote higher ratios. Surface temperatures alone have no impact on snow ratios, unless the temperatures are near or above freezing, then they can actually lower the ratios.
    If any amounts you reported conflict with these amounts, please comment back with your total(s).
    Here is an alternate black and white version of the map:

  4. Quincy
    Two tornadoes (an EF-2 and an EF-1) touched down in eastern New York on Wednesday, both around 7:00 p.m., according to the National Weather Service (NWS).
    The stronger tornado, an EF-2, had winds of up to 125 MPH and caused damage along a relatively wide and long path. The tornado width was estimated at 1 mile wide with a track length of 17 miles from Florida to Rotterdam.
    The second tornado formed just to the southwest of the EF-2 tornado, around the same time. It was a weaker and shorter-lived tornado, but was associated with the same powerful squall line that was moving east-southeast across New York.
    An upper level shortwave disturbance passed across New York state on Wednesday. Daytime heating across the state helped destabilize the atmosphere. Veering winds aloft created an environment that was conducive for the formation of tornadoes.
    I was actually chasing the EF-2 tornado, but was too far west to catch up to it. Heavy rain, flash flooding and traffic didn't help matters. As I drove into the Rotterdam area along I-90, I noticed cars parked under overpasses. While they may have not witnessed the tornado, I'm sure they experienced strong winds and may have been aware of the Tornado Warning. Personally, I did not see a lot of damage, but the tracks of the tornadoes were mainly south of I-90, which was my route of travel.
    PUBLIC INFORMATION STATEMENT
    NATIONAL WEATHER SERVICE ALBANY NY
    1209 PM EDT FRI MAY 31 2013
    ...PUBLIC INFORMATION STATEMENT...
    TORNADO TOUCHDOWN IN MONTGOMERY AND SCHENECTADY COUNTIES ON WEDNESDAY MAY 29 2013.
    LOCATION...
    BEGAN IN FLORIDA IN MONTGOMERY COUNTY NEW YORK TO ROTTERDAM IN SCHENECTADY COUNTY NEW YORK.
    DATE...05/29/2013.
    ESTIMATED TIME...647-700 PM.
    MAXIMUM EF SCALE RATING...EF-2.
    ESTIMATED MAXIMUM WIND SPEED...125 MPH.
    ESTIMATED PATH WIDTH...1 MILE WIDE.
    PATH LENGTH...17 MILES.
    BEGINNING LAT/LON...42.8457/-74.2034
    ENDING LAT/LON...42.8042/-74.0208
    * FATALITIES...NONE.
    * INJURIES...1.
    * THE INFORMATION IN THIS STATEMENT IS PRELIMINARY AND SUBJECT TO CHANGE PENDING FINAL REVIEW OF THE EVENT AND PUBLICATION IN NWS STORM DATA.
    SUMMARY...PATH WIDTH WAS CONSISTENT ALONG THE ENTIRE PATH LENGTH. MAXIMUM DAMAGE INCLUDED ROOFS TORN OFF OF MULTIPLE STRUCTURES AND HIGH TENSION POWER LINE TOWERS TOPPLED. LARGE NUMBER OF HARD AND SOFT WOOD TREES WERE EITHER TOPPLED...UPROOTED AND OR SHEARED. WIDESPREAD POWER OUTAGES OCCURRED AS WELL.
    ******************************************************
    PUBLIC INFORMATION STATEMENT
    NATIONAL WEATHER SERVICE ALBANY NY
    1241 PM EDT FRI MAY 31 2013
    ...PUBLIC INFORMATION STATEMENT...
    TORNADO TOUCHDOWN IN SCHOHARIE COUNTY ON WEDNESDAY MAY 29 2013.
    LOCATION...
    SUMMIT AND EAST JEFFERSON IN SCHOHARIE COUNTY NEW YORK.
    DATE...05/29/2013.
    ESTIMATED TIME...657 PM TO 702 PM.
    MAXIMUM EF SCALE RATING...EF-1.
    ESTIMATED MAXIMUM WIND SPEED...100 MPH.
    ESTIMATED PATH WIDTH...200 YARDS.
    PATH LENGTH...2 MILES.
    BEGINNING LAT/LON...42.515196/-74.554181
    ENDING LAT/LON...42.522471/-74.578385
    * FATALITIES...NONE.
    * INJURIES...NONE.
    * THE INFORMATION IN THIS STATEMENT IS PRELIMINARY AND SUBJECT TO CHANGE PENDING FINAL REVIEW OF THE EVENT AND PUBLICATION IN NWS STORM DATA.
    SUMMARY...BRIEF TOUCHDOWN ALONG RIDGE LINE SEEN FROM JUNCTURE OF DUTCH HILL ROAD AND WHARTON HOLLOW ROAD. DOZENS OF SOFT AND HARD WOOD TREES FALLEN IN DIFFERENT DIRECTIONS AND SHEARED OFF. ALSO TREES DOWN IN DIFFERENT DIRECTIONS ALONG ENID ROAD AND PERAGLIA ROAD.
    Here's a look at radar imagery at 7:00 p.m. when both tornadoes were on the ground:

    Notice overlap of strong bulk wind shear and MUCAPE leading up to the touchdowns:

    Here's a look at storm reports from across the area:

    Here are the tornado tracks to date (2013) in the region:

    Here's a look at my closest pass to the EF-2 tornado, which was basically at the time that it was reported to have lifted off the ground:

  5. Quincy
    Here are some snowfall maps that I created 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.
    A clipper system that gave way to a coastal low just south of Long Island resulted in generally 2 to 4 inches of snow across the state. There were a few localized totals of just over 4 inches, but there were no reports over 5.0 inches. The highest totals were across the higher terrain, where some modest orographic enhancement and/or higher snowfall ratios may have come into play. There was a "snow hole" in southeastern Connecticut where generally 2 inches or less was measured. A few of the higher resolution models hinted at this area of localized lower amounts, but most data pinned that area further north.
    Snow flurries developed around daybreak on December 17th and periods of light snow continued through midday. After a break in the action, an area of moderate to locally heavy snow formed by mid-afternoon as low pressure intensified just to the south. Snowfall rates approached one inch per hour for a time. Some warmer air worked north and there was a change to sleet and freezing rain cross portions of lower Fairfield County. Snow tapered to flurries during the evening hours.
    If any amounts you reported conflict with these amounts, please comment back with your total(s).
    Here is an alternate black and white version of the map:

  6. Quincy
    The potential exists for a low-end severe weather outbreak across portions of the Plains this weekend, April 12th-13th.
    The first focus is on Saturday afternoon into the overnight period across the central Plains. Surface low pressure is forecast to move to a position in the vicinity of the Oklahoma panhandle by 00z Sunday. Now while there is good agreement among the models of destablization in the warm sector, capping will likely mitigate any convective activity for most of the day. However, by late afternoon and into the evening hours enough of the CAP may erode to allow for some isolated severe thunderstorms.
    In the upper levels, a broad positively-tilted trough is projected to be crossing the Rockies late Saturday. The NAM and GFS show an embedded, but small vortmax being ejected northeast from Kansas toward the Missouri/Iowa border Saturday night. Wind fields are not overly impressive and the 18z NAM low level jet appears overdone. With that said, at least 30 knots of bulk wind shear is modeled.
    CAPE values via the NAM and GFS exceed 2000 J/kg from Oklahoma up into Kansas and northern Missouri. The Euro has increased instability somewhat from the 00z run, but only maxes out values around 2000 in eastern Kansas. Given the amount of CIN that has to be overcome, the severe potential here is marginal at best. Given the time-frame three days out, the exact positioning and severity of this threat could shift.

    A somewhat more favorable severe setup may develop on Sunday. As the upper level trough digs into the southern Plains, surface low pressure deepens and slides southeast through Oklahoma and into northern Texas. With the trough axis approaching a neutral tilt, the overall dynamics alone become supportive for severe thunderstorms.
    At the surface, low pressure matures across far northern Texas Sunday afternoon as a strong cold front quickly dives south. A moist southerly flow will aid with moisture transport as dew-points move into the mid and upper 60s. The GFS also shows lifted indicies as low as -12. Ahead of the dryline, a moderately unstable air-mass is forecast on both the GFS and Euro. The GFS has 1500-2500 J/kg of CAPE across eastern portions of Texas into southern Oklahoma with the Euro showing similar instability levels. There should not be much capping, so convective can initiate ahead of the dryline with isolated supercells possible in the warm sector as well.
    Kinematic support increases with bulk shear in excess of 50 knots possible further south of the low across Texas. While damaging winds and hail may be the most significant threats, the setup may also be supportive of at least a few tornadoes. Severe thunderstorms could continue into early Monday, with at that point the cold front should have overtaken the dryline. The result would be more of a squall line with potentially damaging winds than discrete supercell structures. If the somewhat faster GFS is correct, the threat would extend further east into Arkansas and Louisiana.
    While confidence is greater in the severe threat on Sunday, a faster-moving cold front or weaker storm system could alter the forecast. There is relatively narrow window during the second half of Sunday that this system must align with in order for severe weather to be a significant concern. A quick note that the 18z GFS has trended toward stronger kinematic support for Sunday.
  7. Quincy
    Here are some maps that I compiled from various sources. Most of the reports came in through the National Weather Service, with a few from this forum and social media reports that passed through quality control.
    Snowfall amounts were greatest across the higher terrain of Tolland County. This was due to a persistent band of moderate to heavy snow, as well as the altitude as temperatures were marginal through a portion of the event.
    Totals in the Connecticut River valley and the immediate shoreline were generally lower than surrounding areas. If any amounts you reported conflict with these amounts, please comment back with your total(s).
    Here is an alternate black and white version of the map:

  8. Quincy
    I just want to quickly share my latest thoughts for Connecticut and surrounding areas.
    There's little doubt that a strong storm with plenty of precipitation will impact the tri-state area and southern New England Friday into early Saturday, but there are still a few details to discuss.
    Concern #1:
    Mixing along the shoreline. An initially "warm" boundary layer may cause mixed precipitation to fall near the Connecticut shoreline and coastal Rhode Island for several hours. With that said, as low pressure really intensifies southeast of Cape Cod, winds shift to the north and cold air pours on down. This will suddenly change everyone back to snow, even across eastern Long Island.
    Concern? Well, right now I have a wide range of 6 to 12 inches in the forecast. I'm leaning on the higher end of those numbers for coastal sections of Conn. and R.I., but there's still some room for change. These numbers could go higher, although I really doubt they'd trend lower...
    Concern #2:
    Deformation band of intense snowfall. These bands can be difficult to predict with accuracy and a slight shift could be the difference between 8 inches and 18 inches. With that said, I expect this band to impact the eastern half of Conn., especially areas like Tolland, Union and Woodstock that stay all snow and hang onto precipitation the longest. In that band, I am predicting more than 20 inches of snowfall.
    Bottom line...heavy snow, strong winds and coastal flooding are likely. I can see widespread blizzard conditions verifying for IJD, ORH, BOS and surrounding areas. (many areas not included in this map, such as northeastern Mass. and southern N.H.
  9. Quincy
    Here are some snowfall maps that I created 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.
    Flurries began to move into Connecticut shortly after daybreak on January 21st. The snow gradually overspread the state from southwest to northeast and light accumulations were noted across southwestern Connecticut by midday.
    As an area of low pressure developed off the mid-Atlantic coast during the afternoon, a band of heavy snow developed along a SW to NE axis from Philadelphia into Long Island. This band of heavy snow lifted northward and made it about as far as I-84 in Connecticut. Drier air won out on the northwest side of the storm as snowfall totals across Litchfield and Hartford Counties were generally lower than forecast. Areas southeast of the I-95 corridor from Bridgeport to the Rhode Island border also saw less snow, as the heaviest band of snow lifted inland.
    The below radar image demonstrates where the heavy band of snow maxed out. Most of the higher-end snowfall totals were observed in the green shading:

    With low pressure moving eastward early on January 22nd, snow tapered off from west to east during the pre-dawn hours. By daybreak, the accumulating snow was over and air temperatures had dropped into the single digits above, and in some cases, below zero.
    Liquid-to-snow ratios with this storm were fairly impressive. Ratios were commonly in the 20-25:1 range, although some locations observed even greater ratios. Here is a sampling of some of the ratios that were reported:
    North Grosvenordale: 30:1, Oakdale: 26:1, Stratford, 26:1, Portland: 20:1, Essex: 19:1, West Hartford: 18:1.
    The result was a very light and fluffy snow that was very easy to move and shovel. The fluffy nature of the snow also resulted in settling and compaction.
    Here in New Haven, the final snowfall was 8.0". Most of the snow fell before 10 p.m. Snowfall rates averaged around 1" per hour from about 4 p.m. to 7 p.m. when the band of heavy snow moved through the area. The depth of snow as of the afternoon on January 22nd was approximately 6".
    Liquid equivalent precipitation amounts were generally less than modeled across Connecticut. Common values were near 0.2 to 0.3", with lower amounts across north-central and northwestern parts of the state. The SREF data did an excellent job at nailing down a region for heavy snow from the northern half of New Jersey into southwestern Connecticut. It was here that the model showed strong frontogenetical forcing and was eluding to a snowfall maxima. With that said, the SREF and many other models were too generous on the northwest side of the storm for precipitation amounts.
    Here is a black and white version of the map with filtered reports:

  10. Quincy
    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.

    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/
  11. Quincy
    Here are some filtered snowfall maps that I created 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.
    Flurries and light snow moved into Connecticut around daybreak on February 18th as low pressure formed east of New Jersey. The snow moved east and began to develop into a steadier area of snow across New Haven and Middlesex Counties. As a compact, but potent low pressure system developed over Long Island, a band of heavy snow formed near and just east of I-91 from the New Haven area up to the Massachusetts border. Snowfall rates of 1 to 2 inches per hour were observed in many locations.
    The snow changed to a bit of rain across extreme southeastern Connecticut before ending. Some mixed snow and ice pellets were also noted near the shoreline from New Haven and points east during the afternoon.
    Snow ended in northeastern Connecticut by late afternoon. A general 3 to 6 inch snowfall was observed for the eastern half of the state. Less snow fell in western Connecticut and across southeastern sections. There was a narrow band of 6"+, extending from near Meriden, northeastward up to Somers.
    Here in New Haven, the total snowfall was 4.1" Toward the end of the storm, 1.2" of snow fell in just one hour from noon to 1 p.m. The precipitation ended as snow pellets shortly after 1 p.m.
    Here is a black and white version of the map:

  12. Quincy
    An upper level trough across the Great Lakes is associated with areas of surface low pressure in and around New York State. Bands of showers and thunderstorms have been pinwheeling through the eastern United States as a result. By afternoon, more organized thunderstorm development is expected and some storms could become severe.
    Isolated severe thunderstorm threat...
    Low pressure is spinning across New York State. An area of increased wind shear is in place along the east of the Appalachians. Satellite imagery has indicated that much of the region has broken out to at least partial sunshine. This is creating moderately steep lapse rates and with cooler temperatures aloft associated with a 500mb trough, that steepness continues into the mid-levels. A rich southerly flow continues to keep dew-points on the higher side with most stations in the upper 60's to lower 60's.
    As far as forcing goes, there there is a weak frontal boundary movingly slowly eastward across the Appalachians. The higher resolution models couple that disturbance with an unstable air-mass and develop isolated thunderstorms and broken line segments across the Northeast by mid-afternoon.
    Some of the obstacles include a marine influence and some shower activity across southern New England, which may limit just how much the atmosphere can destabilize. However, elevated amounts of wind shear can promote updraft formation and some strong to severe thunderstorms. The coverage of these storms is not anticipated to be widespread in New York and New England. With cooler 500mb temperatures, there is a marginal hail threat with some of the stronger updrafts. Damaging winds seems to be the biggest concern with a relatively low, but still mention-able tornado threat, especially given the relatively low ML LCL's. Climo would not favor widespread severe activity given a south wind, but a coastal front could have some interaction with the upper level setup, which may slightly enhance convective activity.
    Convection is trying to initiate as of midday, but the focus is from early to mid afternoon across the Appalachians and late afternoon in southern New England for any strong to potentially severe storms.
    Numerous severe thunderstorm threat...
    Further south, stronger wind shear combines with more impressive daytime heating to warrant a threat of numerous strong to severe thunderstorms. The focus for this extends from southeastern Pennsylvania and western New Jersey and points southwest. Here there is a threat of large hail, damaging winds and also isolated tornadoes, especially given bulk shear values near or possibly above 50kts this afternoon.

  13. Quincy
    The National Weather Service (NWS) reported that an EF-0 tornado touched down in eastern Massachusetts Thursday afternoon, shortly after 4:30 p.m.
    An upper level low lifted northward through New England on Thursday. An unseasonably cold air mass was in place, resulting in cold temperatures aloft. It was the combination of low Lifted Condensation Levels (LCL's) and moderate wind shear aloft that helped create an environment that was marginally supportive of tornado development. It is possible that a land-sea interaction with winds off of the nearby ocean may have played a role in spawning this tornado. The NWS reported that it was a case of a cold air funnel.
    The tornado touched down in Stoughton, M.A. in Norfolk County and stayed on the ground for 0.25 miles. The tornado was a strong EF-0 with maximum sustained winds of 85 MPH. Damage was minimal, but a local car dealership reported seeing the tornado and had some vehicles blown around by the winds.
    Looking back at historical tornadoes in the Northeastern United States, the helicity values and amounts of instability in place on Thursday were relatively low compared to prior tornadic events. However, it was the low LCL heights and moderate wind shear that did elevate the tornado potential somewhat. On a scale of 0-5, 0 being unfavorable and 5 being highly favorable for tornadoes (based on local climatology), the environment yielded a value of 1.9.
    A note that a 2.5 value would be equal to the mean of past tornadoes.
    PUBLIC INFORMATION STATEMENT
    NATIONAL WEATHER SERVICE TAUNTON MA
    158 PM EDT FRI MAY 10 2013
    ..TORNADO CONFIRMED IN STOUGHTON IN NORFOLK COUNTY MA
    LOCATION...
    STOUGHTON IN NORFOLK COUNTY MA
    DATE...MAY 9 2013
    ESTIMATED TIME...431 PM EDT
    MAXIMUM EF-SCALE RATING...EF0
    ESTIMATED MAXIMUM WIND SPEED...85 MPH
    MAXIMUM PATH WIDTH...50 YARDS
    PATH LENGTH...0.25 MILES
    BEGINNING LAT/LON...42.10N / 71.10W
    ENDING LAT/LON...42.10N / 71.10W
    * FATALITIES...0
    * INJURIES...0
    * THE INFORMATION IN THIS STATEMENT IS PRELIMINARY AND SUBJECT TO CHANGE PENDING FINAL REVIEW OF THE EVENT(S) AND PUBLICATION IN
    NWS STORM DATA.
    ..SUMMARY
    THE NATIONAL WEATHER SERVICE IN TAUNTON MA HAS CONFIRMED A BRIEF TORNADO TOUCHDOWN IN STOUGHTON MA ON MAY 9 2013.
    THE TORNADO TOUCHED DOWN AT A CAR DEALERSHIP ON ROUTE 138 WHERE IT WAS CAPTURED BY A SECURITY CAMERA AND RECORDED ON CELL PHONE CAMERAS BY SEVERAL OF THE DEALERSHIP EMPLOYEES.
    THREE RV TRAILERS...WEIGHING ABOUT 5000 POUNDS EACH...WERE PUSHED BACK ABOUT 6 FEET AGAINST A CHAIN LINK FENCE. ONE TRAILER WAS LIFTED ABOUT 15 FEET INTO A LIGHT POLE BUT LANDED ON ITS WHEELS WITH MINIMAL DAMAGE.
    AN ALUMINUM DOOR ABOUT 20 FEET HIGH AND 15 FEET WIDE WAS BLOWN OUT OF THE SERVICE GARAGE. EYEWITNESSES REPORTED CEILING TILES BEING LIFTED INSIDE THE DEALERSHIP AS THE TORNADO PASSED OVERHEAD.
    THE TORNADO ENTERED A WOODED AREA JUST TO THE NORTHEAST OF THE DEALERSHIP. ABOUT 0.25 MILES AWAY...TWO LARGE PINE TREES WERE DOWNED ON ERICA DRIVE AND DEAN ROAD BEFORE IT DISSIPATED.
    BASED UPON A SURVEY OF THE DAMAGE...THE TORNADO IS CLASSIFIED AS EF0 ON THE ENHANCED FUJITA SCALE WITH MAXIMUM WINDS OF 85 MPH. THE PATH LENGTH WAS 0.25 MILES AND THE MAXIMUM WIDTH WAS ABOUT 50 YARDS.
    Here's a look at radar imagery about a half hour before the time of the tornado:

    The Supercell Composite Parameter was relatively low, although some slightly higher values did target the area near the tornado touchdown:

    The only severe weather report in the Northeast on Thursday was that tornado in Massachusetts!
  14. Quincy
    Here are some snowfall maps that I created 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.
    Light snow overspread the state from southwest to northeast shortly after midnight on February 5th. This was ahead of a low pressure system that was moving into the eastern Ohio Valley. The snow quickly became heavy at times around daybreak, with snowfall rates of 1 to 3 inches per hour. A gradual change to sleet and freezing rain also took place through the morning from south to north. Warmer air flooded in aloft, although there was a cold layer that was very slow to erode near the surface.
    Around midday, there was a break in the action with just some spotty drizzle and light mixed precipitation. The shoreline and parts of eastern Connecticut did briefly rise above freezing. A glaze of ice was observed between I-95 and I-84, with the most significant icing across the climatologically favored sheltered areas of Fairfield and New Haven Counties in the vicinity of Route 15. An inch of sleet was reported in many areas and the size and intensity of sleet that I observed was the most impressive I can ever recall.
    During the afternoon, colder air moved in as a secondary low developed just south of Long Island. Precipitation ended as a few snow showers on the night of the 5th, with a few flurries into the early morning hours on the 6th across eastern Connecticut.
    Snowfall totals between 8 and 10 inches were common. Somewhat less snow fell along the immediate shoreline and in eastern Connecticut. The higher totals were around a foot across central and northwest portions of the state.
    Here is a black and white version of the map with filtered reports:

  15. Quincy
    A colder than average pattern may persist into April across the Great Lakes and Northeast.
    Based on the information I've been reviewing over the past several days, I have enough confidence to post a temperature outlook for the month of April.
    As I see it, below average temperatures will likely continue from the Great Lakes into interior New England and up toward Hudson Bay Canada. I expect a continuation of troughiness extending from southeast Canada into portions of the Northeast. While the heart of the Arctic air should remain well north of the U.S. border, there are other factors coming into play. With the current Great Lake ice coverage being significantly above average, it is going to take quite some time for the ice to melt and for lake-water temperatures to rebound. This means that any wind flow over the lakes will likely bring at least locally cooler temperatures, with transport from cold water to the adjacent land.
    For portions of the Deep South and especially into the southern Plains, I am expecting slightly above to moderately above average temperatures. A gradual re-emergence of a "Southeast Ridge" combined with a general storm track (with shifting entirely possible) through the Ohio Valley and Northeast, warmer air should be able to extend from the lower Mississippi Valley toward the lower Appalachians. Further west, the long-term drought over the central and southern Plains may persist, which is return would tend to allow for higher daytime temperatures than what is observed on average. Temperatures along the immediate Gulf Coast may be able to remain near average, as sea-surface temperatures in the area are running somewhat below average.

    Further speculation into the potential severe weather season leads me to believe that a relatively slow start to the season will continue. With that said, I can see a scenario where the region from the Ark-latex into Mississippi and Alabama has the opportunity for at least a few severe weather outbreaks into the month of April. This is supported by climatology as well, but places such as Kansas, Oklahoma and western Texas may not see a marked increase in severe weather activity until the second half of April. Severe weather forecasting is challenging, because all it takes is one major event to leave a mark. 2013 is a great example, as while the overall year saw below average severe storm reports, there were at least a few particularly damaging events.
    Other supporting references:
    The Euro weeklies and now the extended day Euro ensembles show the Northeastern U.S. trough relaxing north with some ridging (above average temperatures) across the Gulf States. (this is for the final days of March leading into the start of April)
    The CFS up until late last week had a strong lean on well below average temperatures continuing across the Northeast. There has not been the greatest run-to-run continuity, but as of March 18th, there was at least moderate agreement with warming by the 2nd week of April.
    The extended CMC ensembles do show some troughing in the East to start April, despite substantially above average heights in the final days of March in the same area.
    The MJO is forecast by the Euro ensembles to move into Phase 2 and perhaps even Phase 3. The GFS ensembles move the MJO toward the edge of Phases 8 and 1, with the end of the curve clustering into Phase 1. More lean is placed on the Euro solution, however it should be noted that Phase 1 of the MJO favors below average temperatures in the eastern U.S., especially the Great Lakes. Phase 8 is closer to neutral/average. Phases 2 and 3 both match up more closely to Phase 1, with below average temperatures in the East and well below average temperatures from the Great Lakes into New England and southeastern Canada.
    The 1993-94 seasonal analog has matched up in more ways than not to 2013-14. April 1994 saw a return to near and slightly above average temperatures in the East, with some stations reporting well above average temperatures in the Deep South and southern Plains.
    March 1967 has several days that match up closely to the predictions for the latter half of March 2014. April 1967 featured considerably warmer than average temperatures across the southern Plains.

    With all of the factors considered, I think this is a fair forecast to make at this point. Since we're talking about temperatures averaged out for the entire month of April, it's possible that an overall colder than average pattern lingers into the beginning of April before shifting. It is likely that even in such a pattern, we could see a couple of bouts of warmth. A good example is at the end of March. While as of March 18th there was a strong signal for an East Coast low around March 25th-26th, the consensus at this point is that some above average temperatures reach the Northeast once the low passes.
    On Saturday, I said this:
    There is a growing signal of a late-season winter event from March 25-26. However, given the overall troughy pattern expected to start April, there could be yet another winter event between April 1-5.
    I contemplated putting together a precipitation forecast, but rain/snowfall can vary substantially over a region, especially this time of the year. I think the pattern will remain active and perhaps some of this activity could help relax the drought in the Plains come later this spring.
    This was outlook was originally created on Saturday, March 15th, but I have added a few things here and there as new data as arrived. The maps and overall thinking have not changed. This is my first stab at a formal long-range forecast, so a lot will be learned by watching how the trends pan out.
  16. Quincy
    Here are some snowfall maps that I created 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. It should be noted that some of the reports include sleet.
    A general 4 to 8 inch snowfall blanketed the state before a changeover to sleet and in some cases freezing rain/rain. Very few totals deviated from that range, except for a few 8"+ reports in northwestern Connecticut and totals less than 4" across coastal New London County.
    Precipitation came in multiple waves between December 14th and 15th. Periods of light snow fell from morning through early afternoon. Radar imagery showed pronounced dryslots and breaks in the snow shield through much of the afternoon and early evening hours before a slug of heavier precipitation moved back in. This lack of steady snow likely cut down on some of the snowfall totals.
    Warmer air began to work north overnight as low pressure developed along the New Jersey coast. It took quite some time to erode the cold air that was in place prior to the event. Even though areas such as KGON and KIJD changed to rain, KHVN never rose above freezing during the steady precipitation. There, there was even a pronounced temperature drop of 7 degrees within an hour around midnight as the wind shifted to the north, allowing for colder air to drain into the city. As a result, New Haven and nearby North Haven reported an ice accretion of 0.3 inches. Other areas between I-95 and I-84 saw some icing, but most of the freezing rain was confined to lower Fairfield and lower New Haven Counties.
    If any amounts you reported conflict with these amounts, please comment back with your total(s).
    Here is an alternate black and white version of the map:

  17. Quincy
    The National Weather Service (NWS) confirmed that an EF-1 tornado touched down in New York state Friday evening, shortly before 8 p.m.
    A strong cold front moved across Pennsylvania and New York state late Friday evening. At the same time, a marginally unstable air-mass was in place closer to the surface. With moderate to strong wind shear in place and significant storm relative helicity in place, the stage was set for damaging winds and even a marginal tornado threat.
    As a result, a Tornado Watch for a large portion of Pennsylvania and New York state. A tornado touched down near Bainbridge, N.Y. in Chenango County and stayed on the ground for 3.2 miles. The tornado was a strong EF-1 with maximum sustained winds of 110 MPH.
    Looking back at historical tornado environments in the same general area, the wind shear and helicity values in place on Friday were actually more "severe" than the climatological mean for past tornadoes. The only thing that was lacking was instability, as there was very little in place. Despite this fact, strong, twisting and turning winds aloft combined with an approaching squall line ahead of a cold front resulted in the tornado.
    PUBLIC INFORMATION STATEMENT...UPDATED
    NATIONAL WEATHER SERVICE BINGHAMTON, NY
    954 AM EDT MON APR 22 2013
    ...TORNADO CONFIRMED FROM 4 SSE BAINBRIDGE IN CHENANGO COUNTY TO 3 S SIDNEY IN DELAWARE COUNTY NEW YORK...
    UPDATED DATA ON LAT/LON POINTS AND WIDTH.
    LOCATION...
    FROM 4 SSE BAINBRIDGE IN CHENANGO COUNTY TO 3 S SIDNEY IN DELAWARE COUNTY NEW YORK
    DATE...APRIL 19 2013
    ESTIMATED TIME...753 PM TO 758 PM EDT
    MAXIMUM EF-SCALE RATING...EF1
    ESTIMATED MAXIMUM WIND SPEED...110 MPH
    MAXIMUM PATH WIDTH...200 YARDS
    YARDS PATH LENGTH...3.2 MILES
    BEGINNING LAT/LON...42.2481N / 75.4516W
    ENDING LAT/LON...42.2674N / 75.3939W
    * FATALITIES...0
    * INJURIES...0
    * THE INFORMATION IN THIS STATEMENT IS PRELIMINARY AND SUBJECT TO CHANGE PENDING FINAL REVIEW OF THE EVENT(S) AND PUBLICATION IN NWS STORM DATA.
    ..SUMMARY
    THE NATIONAL WEATHER SERVICE IN BINGHAMTON, NY HAS CONFIRMED THAT A TORNADO TOUCHED DOWN ABOUT 4 MILES SSE OF BAINBRIDGE IN CHENANGO COUNTY...TRACKED NORTHEAST ABOUT 3.2 MILES...AND THEN ENDED ABOUT 3 MILES SOUTH OF SIDNEY IN DELAWARE COUNTY NEW YORK FROM 753 PM EDT TO 758 PM EDT ON APRIL 19 2013.
    THE TORNADO TOUCHED DOWN BETWEEN INTERSTATE 88 AND HIGHWAY 206...ON EAST AFTON ROAD...WHERE 2 POWER POLES WERE SNAPPED AND A CAR WAS DESTROYED BY A LARGE TREE BRANCH. ANOTHER VEHICLE WAS ALSO DAMAGED. SEVERAL TREES WERE SNAPPED OR UPROOTED. A BARN HAD MINOR ROOF DAMAGE. THE TORNADO CONTINUED NORTHEAST AND CROSSED HIGHWAY 206...WHERE A FARM EQUIPMENT BUILDING AND A MOBILE HOME WERE HEAVILY DAMAGED...AND A STORAGE TRAILER WAS DESTROYED. OTHER NEARBY HOMES HAD MINOR DAMAGE...AND A CARPORT WAS LIFTED AND MOVED 75 FEETFARTHER DOWN ITS PATH...THE TORNADO INTENSIFIED TO A HIGH END EF1 STRENGTH WHILE TRAVELING IN THE VICINITY OF HOUCK DRIVE. IN THIS AREA IT UPROOTED OR SNAPPED MANY 1 TO 2 FOOT DIAMETER TREES ALONG ITS PATH...BOTH HARDWOODS /MAPLES/ AND SOFTWOODS /PINES/...WITH THE LARGEST MORE THAN 3 FEET WIDE. IT ALSO CAUSED STRUCTURAL DAMAGE TO A SINGLE FAMILY RESIDENCE AND GARAGE...WHILE TRANSPORTING A SIGNIFICANT AMOUNT OF DEBRIS A HUNDRED YARDS OR MORE. THE TORNADO THEN CROSSED INTO DELAWARE COUNTY...DOWNING SEVERAL MORE TREES ON SOME PROPERTIES ALONG HIGHWAY 8 BEFORE DISSIPATING.
    Here's an SPC archived radar image from 00z, just minutes after the tornado touched down. A noticeable kink can be seen along the squall line near the location of the tornado, along with the approximate track below it:


    Here are some more storm reports from Friday:


  18. Quincy
    Just a very brief discussion:
    Low pressure slowly moves east of the mid-Atlantic coast Wednesday night into Thursday. A relatively broad storm with possible multiple low centers spin around and pinwheel periods of snow (some rain mixing in at the coastal plain) through the region from Wednesday into Friday.
    This looks to be an elevation-dependent event, but heavy amounts or precipitation across eastern Mass., eastern Conn. and much of R.I. will help offset some of the "snow losses." In those areas, 1 to perhaps 2" liquid equivalent precipitation could still result in a solid 5-10, perhaps 12" heavy, wet snowfall. The highest risk for 12" would probably be in southern Worcester County.
    Power outages are a concern, especially in southern and eastern areas. There, the water content will be higher and stronger winds are expected.
    Forecast confidence is moderate...the shoreline and southeastern Mass. could see an even sharper gradient. The banding nature of snow and timing with respect to day vs. night will be crucial in determining snowfall amounts. The snowfall totals above are cumulative, so a total of 10" may actually result in a snow-depth of 7" (for example) by midday Friday.
    The computer models are in decent agreement, although the GFS is a lot more conservative than all other guidance. I feel the GFS has had issues with this storm, despite originally bringing it back when the other models were keeping it south. Recall that the GFS backed off on the blizzard the day it started and totals were close to double what it had predicted.
  19. Quincy
    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.

     
    PROS – Favoring 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.
     
    CONS – Limiting 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
  20. Quincy
    I expect light snow to reach the NY/CT and NY/MA border around 9 a.m. or so and then overspread the area from west to east. The heaviest precipitation amounts impact northern Connecticut into central and western Massachusetts.
    Quick warming at 850mb should push most areas over to sleet and freezing rain. The cold layer aloft up to about 925mb looks deep enough where the inland hills may get a thump of sleet, while the interior coastal plain could see several hours of freezing rain.
    By late afternoon precipitation tapers off, but freezing drizzle could linger for many inland areas through much of the night.
    Basically expecting 1-3" of snow and sleet, followed by a glaze of ice for inland areas. Best shot at 3" is across the higher terrain of the Berkshires and Worcester County. Keep in mind that this total accounts for snow AND ice. The only area that is a bit of a question mark is the I-95 corridor (approximately). Will have to keep a close eye on surface temperatures and see how cold air damming is verifying. Right now I think that the immediate coast gets a brief period of snow/sleet/ice and then changes to plain rain. Also, somewhat lighter precipitation amounts here may also result in less of an ability for near-surface temperatures to cool. In a marginal setup, heavier precipitation can help result in more freezing/frozen precipitation.
  21. Quincy
    Here are some filtered snowfall maps that I created 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.
    After early afternoon highs in the lower 60s across much of Connecticut on April 15th, a strong cold front moved through the area at night. Rain quickly changed to sleet and snow across the higher elevations of western Connecticut between 8 and 11 p.m. Although a changeover eventually took place from west to east across most of the state, the heaviest snow fell across western Connecticut. Snow ended before the pre-dawn hours on the 16th.

    Snowfall amounts of 1 to 2″ were common across northern Fairfield and Litchfield Counties. Although there was a gap in the data, it is possible that there were more reports of greater than 2″ across the Litchfield Hills. With this relatively small sample, the highest amounts were from Redding to Roxbury with 2 to 3″ or so. The radar image above left shows a band of heavy snow across northwestern Connecticut shortly after 12:30 a.m. on the 16th.
    As of 2 p.m. on April 16th, temperatures across the higher terrain in western Connecticut were only in the mid to upper 30s. As is often the case with early spring snowfalls, unseasonably cold air followed the snow.
    Here is a black and white version of the map:

    Click here for a complete list of snowfall totals used in these maps.
  22. Quincy
    Low pressure develops across Pennsylvania later today and I am expecting at least some isolated severe thunderstorms across the region.
    Isolated thunderstorm threat...
    Satellite imagery shows mostly clear skies with just some high clouds across eastern Pennsylvania and New Jersey. Daytime heating is expected to push surface temperatures well into the 80's along with dew-points that are already in the upper 60's to lower 70's. In the warm sector well ahead of a cold front (east of the Appalachians in the mid-Atlantic states), a few thunderstorm cells or clusters could develop and become marginally severe this afternoon. As the cold front approaches, a squall line is depicted on the higher resolution models. This may cause isolated wind damage, especially across eastern Pennsylvania and western New Jersey. NAM forecast MLCAPE values are modest at best, near 1000 J/kg in spots. Some hail is possible in the stronger storms, but large hail is not a major threat. Due to the relatively late timing, the severe threat is a bit more unclear across portions of New York State. Even with a loss of daytime heating, proximity to deepening low pressure may cause strong to isolated severe thunderstorms to continue into the overnight period and through the pre-dawn hours of Friday. Although the threat is relatively low due to a lack of directional wind shear, the northern portion of this isolated threat zone will see increased shear after sunset as low pressure amplifies. The late timing does not climatologically favor nighttime tornadic development, but a quick spin-up could be possible, mainly in northeastern Pennsylvania, northwestern New Jersey and portions of southern New York State.

    In Connecticut...
    Although skies are breaking for sunshine across southwest portions of the state, there is a lack of a trigger mechanism to fire off any storms. MLCAPE values may increase to near 500 J/kg in parts of the state. SBCAPE looks more impressive, but with poor mid-level lapse rates, severe thunderstorm activity is not anticipated. Some pop-up thunderstorms are possible late in the afternoon and some embedded thunderstorms are expected overnight, especially west of the Connecticut River.
  23. Quincy
    There was a lot of anticipation leading up to July 15th. Some argued there was a "very impressive" severe setup unfolding for (southern) New England, but there was plenty of disagreement with the placement and potential severity of such an event.
    For a quick summary, the severe weather parameters in place (both forecast prior and during) the event were marginal compared to past severe events in southern New England. Not one important severe weather parameter was terribly impressive and there were many pieces to the puzzle that were missing here.
    As of July 17th, there have only been a handful of severe wind reports, centered over a small geographical area between far northeastern Massachusetts and adjacent far southeastern New Hampshire. There were a few damaging wind reports in downeast Maine, along with two marginally severe hail reports. Although there were several tornado warnings in the area, only one tornado has been confirmed so far. That was an EF-1 in Somerset County, Maine. (this blog post will be edited if any additional tornadoes are confirmed) Flooding was more of a widespread issue across much of New England and extending down into the NYC metropolitan area and New Jersey.
    There are some misconceptions as to what constitutes as a “significant” or “impressive” severe setup in New England. Generally almost all significant severe outbreaks occur with a west to northwest flow aloft and an anomalously strong overlap of shear (speed and directional) and instability. While it’s not uncommon to see strong instability and significant wind shear in this part of the country, they don’t often coincide with each other. There are other setups too, which are usually more marginal, sporadic and difficult to forecast. While some southwest to southerly flow events have produced severe, unless key ingredients are in place, those events usually only result in widely scattered or isolated severe reports.
    This event was well-modeled in the synoptic view. There was an anomalously strong upper level cutoff low moving into the Great Lakes. Ahead of this feature, there was a surface cold front advancing through Pennsylvania and New York with a pre-frontal/lee-side surface trough axis across New England by the morning of July 15th.
    While this may sound like a good setup, as often is the case in this part of the country, many additional things have to line up just right. If one or two (or more) variables don’t pan out right, then the whole setup will likely underperform compared to expectations. Timing was also another issue, as with the cutoff low displaced so far west from New England, the best forcing would also remain further west.
    The mesoscale models were predicting anywhere from 500 to 1,250 J/kg of MLCAPE (with somewhat greater SBCAPE) coinciding with 30-40 knots of bulk shear across central New England and portions of western southern New England. While both parameters are what can be considered “elevated,” they are on the low end (lower 50 percentile) for what has been observed in the Northeast in prior tornado cases. When looking at severe producing supercells in general (all types/modes), the values mentioned above are actually even less significant. Consider that the mean bulk shear value for supercells in the southwestern New England window* is 44 knots with a mean MLCAPE value of 1,421 J/kg.
    So, there were two key parameters in place that were elevated, but not terribly impressive in comparison to past severe events. There is another piece here that made the whole setup look even more marginal. Storm relative helicity or SRH (effective) was very meager on the computer forecast models for July 15th across most of the area. The progs were only between about 50 and 100 m2/s2. This is again on the low end, when considering that the mean SRH value for tornado and supercell cases alike in the area is 139 m2/s2 (which some cases over 300 m2/s2).
    While looking at this forecast setup from a strict numerical standpoint, while the threat of tornadoes and other severe weather were somewhat elevated, it was clearly a “below average,” or in other terms, an “unimpressive” setup.
    As far as the model simulated radar guidance, the NAM struggled to develop much in the way of discrete cell activity across southern New England, instead favoring a line of thunderstorms moving in from eastern New York by late afternoon and evening with stronger forcing ahead of the cold front. The HRRR was a bit more alarming, with a line strong to severe cells and clusters moving into southwestern New England by late afternoon. The HRRR by the 11z and 12z runs were showing some weak convection along the pre-frontal trough giving way to stronger convection further west later on.
    The morning of July 15th:
    Convection was already firing along the pre-frontal trough by midday, but due in part to limited heating, and weak forcing, the activity across Connecticut and south-central Massachusetts never reached severe limits. The HRRR continued to show stronger activity later in the day, but later runs gradually backed off on that idea. It was clear from the start that there was also a fairly unidirectional shear pattern with not much backing of low-level winds. Surface observations through the entire event, including the early to mid morning hours, showed surface winds S to SW.
    It cannot be overlooked that a small area from northeastern Massachusetts into southeastern New Hampshire and much of Maine did see scattered strong to severe thunderstorms develop later on during the afternoon.
    Analyzing the severe weather parameters on July 15th:
    The models did a good job of predicting wind shear, as the SPC mesoscale analysis showed an average of about 40 knots of bulk shear across the area, with more across northern and northwestern sections and less across southern and southeastern sections. MLCAPE was also close to model guidance with generally 1,000 J/kg, on average. The pre-frontal activity did decrease instability across Connecticut with a noticeable uptick in CIN, especially in the vicinity of the trough. It was across northeastern Massachusetts and points northwest where less CIN and more significant SBCAPE values supported more in the way of storms being able to reach marginally severe limits.
    Taking a step back, the mid-level lapse rates were fairly unimpressive across the area and this was acknowledged by SPC leading up to the event. The reanalysis showed lapse rates of 5.5 C/km or less across much of southern New England, with some lapse rates over 6 C/km across Maine.
    Upper level considerations:
    Analogs very strongly favored a relatively low-end severe event, especially given the position of the upper level low and the fact that the flow aloft was out of the SW. The RAP analysis from July 15th shows that the most significant vortmax was located very close to the upper level low, which was west of even western New York. There was some positive vorticity advection across northern New England, which likely was a factor in boosting some of the severe thunderstorms north and northwest of Boston, Mass. The mesoanalysis showed a weak, elongated vortmax between 18z on the 15th and 00z on the 16th, but this was up across northern Vermont and the northwestern Maine/Canada border.
    Finally, when also looking at the upper level flow, it was once again below climo levels with respect to significant severe events. The GYX and OKX soundings showed just 40 knots and 39 knots respectively of 500mb flow at 12z on the 15th. The upper level flow actually decreased notably at OKX to 31 knots by 00z on the 16th. While severe events can occur in the Northeast with limited upper level flow, the more impressive events typically have much stronger flow aloft. It should also be mentioned that the 850mb jet was unimpressive, with wind speeds of just 20 to 30 knots. Only one run of the Euro showed a signal of a strong jet and that was 144 hours prior, when it was predicting 45-55+ knots of 850mb flow.
    The relatively weak flow and generally unidirectional shear pattern can be seen clearly in the 12z July 15th OKX sounding:

    Considering the mesoscale models:
    The HRRR performed poorly on the larger scale, as it did not show pre-frontal activity contaminating the environment across southwestern New England. Instead, it was more optimistic in terms of severe and even showed somewhat alarming significant tornado parameter values over 1 across much of Connecticut. Although some convection did cross over from Long Island into Connecticut, this wasn’t until late at night and most of that activity was marginally severe or below severe limits. Some fairly weak storms did fire across eastern New York by late afternoon, but those merged with other convection to form a very messy storm mode, one that favored training of heavy rains and flash flooding. The models also showed more backing of low-level winds than what was observed on the morning of July 15th and through the event.
    In summary, what went wrong?
    While it’s easy to blame the entire bust on early day convection across Connecticut, consider again the forecast parameters in place that verified very closely to the actual analysis. Instability was somewhat elevated, but still modest at best with around 1,000 J/kg of MLCAPE. Shear was also elevated, but 40 knots of bulk shear is somewhat below the average for past severe cases. One of the most glaring parameters missing from the equation was helicity. Helicity was expected and verified to be quite low on the spectrum, with 100 m2/s2 at best, while tornado activity favors more than that. With a SW flow aloft, a more strongly backed low-level wind profile would have supported a greater threat of severe. Instead, any backing was minimal, with the mean low-level wind flow being S to SW. It would have been one thing if mid-level lapse rates were impressive, to offset some of the other marginal parameters, but 5.5 C/km is not going to make up for everything else.
    *
  24. Quincy
    Here's a recap of the 2013 tornado season across the Northeast.
    Connecticut had four reports of tornadoes during 2013, which is roughly twice the average amount of about two. Keep in mind that 2012 had no tornadoes in the state, so one could argue that this was nature's way of balancing itself out.
    Elsewhere, New Jersey was the only other state in the Northeast with above average tornado reports. (They average two per year, but had three in 2013) Maine is not pictured here, but Maine had at least two tornado reports. Since they average two per year, that's right at average. Massachusetts also saw an average year with one tornado report. Vermont and New Hampshire typically average about one tornado per year, but both states saw no tornadoes this year. New York was well below average with just four tornadoes. The average there is 10 per year. Pennsylvania reported nine tornadoes, also well below their average of 16 per year.
    Averages based off of 1991-2010 reports, per NCDC.
    April 19th: An EF-1 tornado touched down near Bainbridge, N.Y. and was on the ground for 3.2 miles. (link)
    May 9th: A weak EF-0 tornado touched down near Stoughton, Mass., but the length of damage was less than 0.5 miles. This was a cold air funnel case and not a "classic" tornado. (link)
    May 28th: There were four tornado reports across northwestern Pennsylvania. Three of the tornadoes were rated EF-1s and one was an EF-0. The longest tracking tornado was an EF-1 that touched down near Edinboro and had a damage path of 18 miles long.
    May 29th: Two tornadoes were reported in eastern New York State. One was a significant, long-track tornado (EF-2). It was on the ground for 17 miles and the damage path was up to 1 mile wide. Another tornado, a weaker EF-1, was reported just to the southwest of that storm. (link)
    June 2nd: Two brief and weak EF-0 tornadoes were reported in Maine.
    June 27th: Two EF-1 tornadoes were reported in central Pennsylvania.
    July 1st: A somewhat unusual morning tornado (EF-1) was reported in extreme northeastern New Jersey. The same storm that was responsible for that tornado resulted in three tornado reports across Connecticut from late morning into early afternoon. The first report was an EF-0 that touched down in Greenwich. The most notable tornado was the second one, which was an EF-1 in the Windsor and Windsor Locks areas. A weak, brief EF-0 tornado was the third report in Enfield. (link)
    July 10th: A brief EF-1 tornado was reported near Moravia, Penn. during the afternoon. Less than an hour later, an intermittent EF-1 tornado was reported in Connecticut between Andover and Mansfield. The damage path of that tornado was 11.2 miles long.
    July 27th: An EF-1 tornado was reported in north-central Pennsylvania near Borie. That same storm dropped another EF-1 tornado in adjacent New York State about an hour later. The second of those two tornadoes was on the ground for 14 miles.
    August 7th: A minor EF-0 tornado was reported in southwestern Pennsylvania near Ralphton.
    August 13th: A weak EF-0 tornado was reported near Manahawkin, N.J.
    October 7th: An EF-1 tornado was reported near Paramus, N.J.
    The tornadoes pictured above across Delaware, Maryland and Ohio were not included in the above time-line.
    As might be expected, the strongest and longest-tracking tornadoes across the Northeast this year were across New York and northwestern Pennsylvania.

    Those areas are climatologically favored for significant tornadoes, at least when compared to areas further east. With that said, there have certainly been cases of strong tornadoes in southern New England. The most recent case was the deadly EF-3 tornado that tracked across south-central Massachusetts on June 1st of 2011. The above image is a composite that is not perfectly to scale.
    United States tornado seasons:
    Through then winter, the Gulf States are favored for tornado development. There was a minor event this past Sunday, on January 12th, that featured a few EF-0 tornado reports in extreme southeastern Virginia. Into spring, the focus shifts toward the Midwest and late spring into early summer is when the Northeast most commonly sees tornadoes.

  25. Quincy
    A 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.

    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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