Severe weather risk 4/30 - 5/3

[weatherextreme]

Lets get this started. 

 

Outlook for 4/30 - 5/2

 

 

 

 

Day 1 Convective Outlook CORR 1
   NWS Storm Prediction Center Norman OK
   1144 AM CDT Tue May 01 2018

   Valid 011630Z - 021200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS CENTRAL KS...

   CORRECTED FOR CATEGORICAL GRAPHIC

   ...SUMMARY...
   Numerous severe storms are expected over the central Great Plains to
   the Mid-Missouri Valley. The most likely corridor is across parts of
   central Kansas between 5 to 9 PM CDT. Tornadoes, a couple of which
   could be strong, very large hail, and damaging winds will be
   possible.

   ...Central Great Plains to the Upper MS Valley...
   12Z soundings across central OK and north-central TX sampled mean
   mixing ratios near 12 g/kg within a plume of 63-64 F surface dew
   points. Richer moisture with upper 60s and lower 70s dew points
   remains confined to south TX this morning. This suggests
   boundary-layer moisture return is probably one day too early from
   being optimal for a regional severe weather/tornado outbreak. Even
   so, confidence is relatively large in storm initiation and probable
   evolution in the late afternoon and evening, rendering increased
   large hail probabilities. 

   The dryline is expected to mix across the eastern TX Panhandle and
   western KS as surface temperatures warm into the 80s, creating a
   T-intersection with a quasi-stationary front arcing across
   west-central KS into eastern NE. A broad plume of MLCAPE from
   2000-2500 J/kg is anticipated ahead in the warm/moist sector.
   Guidance is consistent in ejecting a mid-level speed max ejects from
   the southern High Plains into KS by 00Z. This should aid in ascent
   for probable storm development in the 20-22Z time frame along the KS
   portion of the dryline. Decreasing certainty exists farther south
   along the dryline where weak mid-level height rises are anticipated
   to occur this evening as the broader trough over southern CA digs a
   bit farther south.

   50-kt effective shear, nearly perpendicular deep-layer winds to the
   dryline, and rather steep mid-level lapse rates will favor discrete
   supercells producing very large hail. A few of these supercells may
   become long-tracked across central KS and the threat for tornadoes
   will increase between 22-02Z as storms encounter richer
   boundary-layer moisture (toward the I-135 corridor) and as low-level
   shear increases rapidly in response to a strengthening low-level
   jet. The synoptic pattern is largely consistent with past Great
   Plains cases of the evening low-level jet strengthening and aiding
   in mid/late evening significant tornadoes. However, low-level
   moisture may remain on the lower margins of what is typical of the
   high-end events (with similar temperature profiles and hodograph
   structures). The slightly drier boundary layer will encourage a
   little quicker increase in convective inhibition, coincident with
   the strengthening low-level shear. Thus, it is not clear whether or
   not this scenario will evolve into a long-lived significant tornado
   threat near sunset, or if the inhibition increase will tend to limit
   the window of opportunity. Otherwise, clusters of storms (with
   embedded supercells) should persist well into the overnight hours
   with an attendant threat for large hail/damaging gusts and a couple
   tornadoes, from the triple point northeastward along the
   quasi-stationary front into the Upper MS Valley.

   ...Northeast CO...
   An upslope flow regime will help maintain boundary-layer dewpoints
   in the 40s across northeast CO through the afternoon, north of a
   stalled front. Surface heating in cloud breaks will yield weak
   surface-based buoyancy, while deep-layer vertical shear will be
   favorable for supercells. A couple supercells may form this
   afternoon in conjunction with the northern periphery of the
   mid-level speed max ejecting into KS. These storms should move east
   before weakening by mid-evening.  Isolated large hail and strong
   wind gusts will be possible.

   ..Grams/Goss/Wendt.. 05/01/2018

 

 

 

   .

Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1251 AM CDT Tue May 01 2018

   Valid 021200Z - 031200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE SOUTHERN/CENTRAL PLAINS...

   ...SUMMARY...
   Severe thunderstorms are expected across parts of the southern and
   central Plains mid-day Wednesday through the overnight. Large hail,
   damaging winds, and a few tornadoes will be possible. Isolated to
   scattered severe storms may also develop across parts of the
   Midwest, with hail and damaging winds the primary threat.

   ...Discussion...
   The D2/Wednesday convective outlook presents a challenging forecast
   scenario, owing to the subtle nature of multiple impulses advancing
   across the Plains within a corridor of weakly anticyclonic flow.
   Most guidance indicates this evolution will result from continued
   digging of the western US trough on Tuesday, with subsequent closed
   low development within the broader trough. In turn, rising heights
   over the Plains should yield weak ridging aloft by Wednesday
   morning. At the surface, a front is forecast to extend from western
   Kansas east/northeastward to Wisconsin, while a dry line will be
   positioned from the front in Kansas south/southwestward into west
   Texas.

   ...Southern Kansas to the Missouri Valley...
   A weakening/veering low-level jet is expected to extend across
   eastern Kansas Wednesday morning. Through the late morning and
   afternoon, though, low-level flow should back slightly ahead of a
   triple point over southern Kansas. In turn, increasing warm
   advection and convergence is expected to support convective
   initiation over parts of southern/central Kansas. Meanwhile,
   southerly flow will transport dew points in the mid 60s over the
   area, supporting moderate mixed-layer buoyancy by afternoon.
   Organized by southwesterly mid-level flow around 45-55 kt, several
   cells should become severe, initially capable of large hail and
   damaging winds.

   Mode evolution (i.e., discrete cell potential) remains questionable
   with this earlier convection, as the orientation of the larger-scale
   pattern and resultant veered 700mb flow may encourage straight
   hodographs, or perhaps some counter-clockwise curvature in mid
   levels. Therefore, storms may grow upscale into eastward-advancing
   linear segments, with damaging winds as the primary threat over
   parts of central/eastern Kansas. Concurrently, any higher tornado
   potential may not increase until late evening, as the low-level jet
   increases, and convective bands potentially acquire embedded
   rotating elements.

   ...Oklahoma into northwest Texas...
   Convective coverage may be sparse through much of the day, given
   somewhat veered flow aloft, increased drying over far western
   Oklahoma, and weaker convergence along the dry line initially.
   However, as the low-level jet intensifies towards 00Z, a combination
   of increasing low-level shear, a moistening boundary layer, and
   steep mid-level lapse rates will yield a conditional threat for a
   few intense storms, capable of very large hail, damaging winds, and
   tornadoes. Still, considerable uncertainty exists regarding the
   potential for sustained convective development during the evening,
   owing to some of the issues described above. Moreover, similar to
   Kansas, counter-clockwise hodograph curvature aloft would support a
   few sustained left splits, interfering with the potential for
   longer-tracked discrete supercells. Considering these caveats, the
   ongoing enhanced is maintained with minor changes.

   As broader/stronger deep ascent overspreads the Plains (and a
   distinct corridor of low-level flow/moistening organizes to the
   west), a separate round of convection is possible from west Texas
   into the Panhandle and western Oklahoma Wednesday night. While the
   parameter space may remain favorable for tornadoes and large hail,
   continued dry air aloft, questionable mid-level wind profiles, and
   related mode issues may also yield upscale growth into
   eastward-accelerating bands, with damaging winds as the primary
   threat.

   ...MAXIMUM RISK BY HAZARD...
   Tornado:  10% SIG - Enhanced
   Wind:     30%     - Enhanced
   Hail:     30% SIG - Enhanced

   ..Picca.. 05/01/2018

 

 

 

 

[weatherextreme]

Looks like Accuweather is already calling this system the 'Biggest storm outbreak of the year."

 

 

 

"Biggest severe storm outbreak of year likely next week for parts of central US spared thus far this season"

 

https://www.accuweather.com/en/weather-news/severe-thunderstorm-outbreak-to-likely-strike-plains-mississippi-valley-first-week-of-may/70004788

[Upper Level LOL]

12 minutes ago, weatherextreme said:

Looks like Accuweather is already calling this system the 'Biggest storm outbreak of the year."

 

 

 

"Biggest severe storm outbreak of year likely next week for parts of central US spared thus far this season"

 

https://www.accuweather.com/en/weather-news/severe-thunderstorm-outbreak-to-likely-strike-plains-mississippi-valley-first-week-of-may/70004788

Wow, when did they hire Broyles away from the SPC?

 

But seriously though that's a bit bullish at this stage. It may turn out accurate, but those sorts of statements are pretty irresponsible for something that's still 5-6 days away

[hlcater]

Monday and Thursday may have some mild potential as well depending on what model you look at.

[jojo762]

12Z euro continues to depict rather impressive environments on both Tuesday and Wednesday along the dryline and the triple-point. With Wednesday still looking more like "the day."

Monday has the potential to be very interesting as well along the dryline pending at least scattered/isolated storm development. Ample kinematics in place, moisture is obviously a bit less than ideal for Monday, but should have fairly impressive parameters in place nonetheless. GFS attempts to fire off storms in E TX PH/W OK... GFS forecast soundings for that area are highly favorable for supercells and perhaps tornadoes. (~2500 J/KG MUCAPE, 50+ KT cloud-bearing shear, 0-3KM SRH of 400+ m2/s2, fairly minimal CIN... perhaps the most impressive part is the degree of directional shear in the entire column, and critical angles of ~90-degrees.)

[andyhb]

1 hour ago, jojo762 said:

12Z euro continues to depict rather impressive environments on both Tuesday and Wednesday along the dryline and the triple-point. With Wednesday still looking more like "the day."

Monday has the potential to be very interesting as well along the dryline pending at least scattered/isolated storm development. Ample kinematics in place, moisture is obviously a bit less than ideal for Monday, but should have fairly impressive parameters in place nonetheless. GFS attempts to fire off storms in E TX PH/W OK... GFS forecast soundings for that area are highly favorable for supercells and perhaps tornadoes. (~2500 J/KG MUCAPE, 50+ KT cloud-bearing shear, 0-3KM SRH of 400+ m2/s2, fairly minimal CIN... perhaps the most impressive part is the degree of directional shear in the entire column, and critical angles of ~90-degrees.)

Moisture is almost certainly going to be a problem for Monday bar a drastic change. Just not enough time for return flow after the FROPA in the Gulf. What would be more interesting is if Monday slows down, eliminating that potential, then Tuesday and Wednesday (with better moisture in place) likely have better synoptics/timing.

[mfgmfg]

I'm smack in the middle of this

[Weatherdemon]

1 hour ago, mfgmfg said:

I'm smack in the middle of this

 

Me too.

I already took Wed off. May run out west Tuesday and follow it back home then do it again Wednesday.

[Radtechwxman]

Noticing some VBV showing up in soundings. Obviously the orientation and amplitude of this trough will be crucial to how that plays out. Def hope we get secondary low development like Euro shows as the main jet ejects out Wed. GFS seems to make the early week low the main one and doesn't really form another one and this causes the wind fields to get messy south. So a lot of details to iron out but the instability and moisture and overall synoptics will be there for a few active severe wx days

[nrgjeff]

Slight VBV can be overcome in an otherwise good set-up. For next week good SW to at times WSW flow upstairs is forecast. If a couple levels waver a bit, without going far, it is still a great hodograph. At least it is not a bowling ball with that ugly south wind at all levels. In contrast to previous systems, these (forecast) winds are plenty good enough to support sustained updrafts separated from the front flank. Moisture will be the challenge though.

[Radtechwxman]

29 minutes ago, nrgjeff said:

Slight VBV can be overcome in an otherwise good set-up. For next week good SW to at times WSW flow upstairs is forecast. If a couple levels waver a bit, without going far, it is still a great hodograph. At least it is not a bowling ball with that ugly south wind at all levels. In contrast to previous systems, these (forecast) winds are plenty good enough to support sustained updrafts separated from the front flank. Moisture will be the challenge though.

See I'm more worried about upper level winds than moisture. Seen some ugly S shaped hodos. Yes it isn't like due south upper levels like the last setup but would still like to see a bit more directional change from 500 to 300mb. But at least the lower levels have good turning. Moisture will def be an issue Mon, maybe slightly Tues, but should be plenty deep by Wed

[WhiteoutWX]

I can’t remember a plains setup in the past 3 years that didn’t have VBV worries leading into the event.

[the ghost of leroy]

i'll be out tuesday and wednesday if things fire off.  looking forward to ending this tornado drought.

[Radtechwxman]

8 minutes ago, WhiteoutWX said:

I can’t remember a plains setup in the past 3 years that didn’t have VBV worries leading into the event.

Yea you got a point. Hard to get quality wind fields anymore. But like nrgjeff said, as long as everything else falls into place we should be good. I just hope we get secondary low development like Euro shows cuz if not the llj could get displaced by that early week low in the northern Plains and low level winds could veer

[CheeselandSkies]

11 minutes ago, StormChaser4Life said:

Yea you got a point. Hard to get quality wind fields anymore. But like nrgjeff said, as long as everything else falls into place we should be good. I just hope we get secondary low development like Euro shows cuz if not the llj could get displaced by that early week low in the northern Plains and low level winds could veer

Maybe this discussion is better suited for its own thread, but any thoughts as to why that is? Something to do with the global circulation pattern? Can't be ENSO alone since we've had El Nino, La Nina and near-neutral conditions in that time.

There are some periods (May 4-10, 2003, May 22-30, 2004, May 22-June 11, 2008, pretty much all of April 2011) where every trough that comes through can seemingly produce a significant tornado outbreak at will, but that hasn't been observed for quite awhile.

 

[bjc0303]

Moisture will almost certainly NOT be an issue Tuesday, and will be plentiful Wednesday with low 70s appearing in even some euro progs. 

[Stebo]

The VBV is so marginal, so tired of people latching onto the tiniest bit of VBV and saying it is a deal breaker. This isn't like previous potentials over the last few years where there was massive backing aloft.

[bjc0303]

Yeah what some are calling VBV is actually just veering followed by predominantly speed shear (with the tiniest hint of backing). 

[Radtechwxman]

1 hour ago, CheeselandSkies said:

Maybe this discussion is better suited for its own thread, but any thoughts as to why that is? Something to do with the global circulation pattern? Can't be ENSO alone since we've had El Nino, La Nina and near-neutral conditions in that time.

There are some periods (May 4-10, 2003, May 22-30, 2004, May 22-June 11, 2008, pretty much all of April 2011) where every trough that comes through can seemingly produce a significant tornado outbreak at will, but that hasn't been observed for quite awhile.

 

We just seem to get in these blocky patterns and also get these deep troughs with high amplitude. Those years seem to have more low amplitude faster moving troughs. I really prefer broad based troughs over a tight deep trough which tend to see more issues with winds aloft. But this def looks like the best stretch of severe weather in the Plains in a while and I'm really excited for the potential. I don't see moisture being an issue at all. Comes down to timing of waves and associated sfc pattern

[andyhb]

Well the 00z runs so far certainly aren't confidence boosting in anything that significant next week. Poor trough ejections galore.

[TXHawk88]

SPC going with a pretty good size 30% risk area on Day 6  (Wednesday) I can’t remember the last time I’ve seen that. It will be interesting to see how things shape up over the next 120+ hours. 

 

[OUGrad05]

30% is surprising on a D6 IMO, especially with some many small details yet to be ironed out.  I like what I'm seeing at this point for possibilities and am desperate for a chase.  Euro is more bullish than GFS so there's that.

[Radtechwxman]

Yea I'm not sure why SPC went 30% this far out esp given the uncertainty. Really starting to fear the ill timed waves on models. Would be disheartening to see three days of nothing good to chase. Still got several days....hope it will change but unfortunately a slowing trend makes more sense

[OUGrad05]

12 minutes ago, StormChaser4Life said:

Yea I'm not sure why SPC went 30% this far out esp given the uncertainty. Really starting to fear the ill timed waves on models. Would be disheartening to see three days of nothing good to chase. Still got several days....hope it will change but unfortunately a slowing trend makes more sense

Sure but it's D5 and D6.  If it was perfect it would fall apart at D3 or so.  Too many mesoscale features won't be resolved until the system is fully sampled which won't really happen till Sunday.  Ingredients are going to be "around" so the question comes down to timing.  Too soon to get hyped and too soon to write it off.  

I do agree a slowing trend wouldn't be surprising.  

[CheeselandSkies]

4 minutes ago, OUGrad05 said:

Sure but it's D5 and D6.  If it was perfect it would fall apart at D3 or so.  Too many mesoscale features won't be resolved until the system is fully sampled which won't really happen till Sunday.  Ingredients are going to be "around" so the question comes down to timing.  Too soon to get hyped and too soon to write it off.  

I do agree a slowing trend wouldn't be surprising.  

I think I'm not the only one antsy for a high-confidence, long lead time synoptically evident outbreak sequence that's good for several days of hype and then actually pans out.

[OUGrad05]

Just now, CheeselandSkies said:

I think I'm not the only one antsy for a high-confidence, long lead time synoptically evident outbreak sequence that's good for several days of hype and then actually pans out.

No doubt

[Radtechwxman]

5 minutes ago, OUGrad05 said:

Sure but it's D5 and D6.  If it was perfect it would fall apart at D3 or so.  Too many mesoscale features won't be resolved until the system is fully sampled which won't really happen till Sunday.  Ingredients are going to be "around" so the question comes down to timing.  Too soon to get hyped and too soon to write it off.  

I do agree a slowing trend wouldn't be surprising.  

Almost seems like the trough is getting too positive tilt. The speed max really struggles to round the base quick because of the sharp tilt. Def agree it's too early to make any call. Everything looks to be in place, esp by Tues, so just need the waves to time better. 

[nrgjeff]

SPC 30% is justified based on broad pattern recognition. Plus the ECMWF still has a robust look. All models are pretty consistent for a week out. Remember 30% is just Enhanced, still Slight in Old School, nothing crazy. We will have excellent turning with height up to 700 mb. Speed shear will be robust all the way up. Moisture is not a question Wednesday. When a shortwave ejects within southwest flow in early May.. Look for fireworks!

Travelers: Still keep all days next week open. Remember it is sometimes/often the day before the day. Also the trough could slow down. If you live out there.. I'm homesick, lol!

[bjc0303]

1 hour ago, StormChaser4Life said:

Yea I'm not sure why SPC went 30% this far out esp given the uncertainty. Really starting to fear the ill timed waves on models. Would be disheartening to see three days of nothing good to chase. Still got several days....hope it will change but unfortunately a slowing trend makes more sense

A slowing trend would actually be beneficial...

[CheeselandSkies]

17 minutes ago, nrgjeff said:

SPC 30% is justified based on broad pattern recognition. Plus the ECMWF still has a robust look. All models are pretty consistent for a week out. Remember 30% is just Enhanced, still Slight in Old School, nothing crazy. We will have excellent turning with height up to 700 mb. Speed shear will be robust all the way up. Moisture is not a question Wednesday. When a shortwave ejects within southwest flow in early May.. Look for fireworks!

Travelers: Still keep all days next week open. Remember it is sometimes/often the day before the day. Also the trough could slow down. If you live out there.. I'm homesick, lol!

Yes but it's also technically as high as they can go beyond Day 3, so IMO it should carry the implication of something higher end (>30% ENH by the time DY1 rolls around). Was a time when if they went MDT on DY2, you knew all **** was going to break loose.