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cheese007

Severe Weather May 13-15th, 2020

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ZCZC SPCSWOD48 ALL
   ACUS48 KWNS 090856
   SPC AC 090856

   Day 4-8 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0356 AM CDT Sat May 09 2020

   Valid 121200Z - 171200Z

   ...DISCUSSION...
   Medium-range guidance is in good agreement that the upper pattern
   will trend more zonal by early next week, favoring deeper lee
   troughing and low-level moisture return across the Plains. The upper
   pattern is forecast to remain void of any systems strong and/or
   mature enough to scour the low-level moisture out of the Plains or
   MS Valley through the end of next week, setting the stages for an
   active week as subtle shortwave troughs and their attendant surface
   lows/front interact with the moist low levels. 

   On each day the previous day's convective evolution will have a
   large influence on severe potential, leading to generally low
   predictability. The only exception is D5/Wednesday, which looks to
   be the first day where the favorable low-level moisture is far
   enough north of interact with a subtle shortwave ejecting into the
   central Plains. Supercell wind profiles and steep lapse rates will
   be in place to support severe potential with any storms that develop
   along the dryline. Severe potential exists on D6/Thursday,
   particularly from the central Plains into the mid MS Valley, but
   limited predictability and questions regarding the northeastward
   extent of the moisture return preclude outlooking any areas yet.

   Model solutions begin to diverge more after D6/Thursday, limiting
   forecast confidence. However, with favorable low-level moisture
   expected to remain in place across the Plains, some severe threat
   will persist into the weekend.

   ..Mosier.. 05/09/2020

Screenshot_20200509-113507_Chrome.jpg

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Definitely looks like multiple days of potential middle to end of next week. Mid to upper flow is relatively weak but adequate for some slow moving supercell potential. GFS lights up the dry line each day. It’s been a slow start in the plains but that looks to be changing quickly.

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Probably could go ahead and make this thread for the 13th through the 15th, as Friday appears to have at least some severe potential as well attm. Probably not looking at a day with widespread outbreak potential necessarily, but certainly looking at a period that could end up having “Classic” May chase days, for sure. Wednesday looks fun, and I’m curious to see what the NAM ends up showing when it gets in range. 

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ICT already discussing potential for tornadoes on Wednesday/Thursday in their AFD. 

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This thread sure is dead. Lol. I do like the upcoming potential this week. Good moisture and instability though nam is keeping it more into OK and less into KS. A lot of this week, minus a shortwave on Wed, will be mostly mesoscale related details. I'm not a fan of the overall weak wind fields but the chance of discrete development on a sharp dryline is pretty good esp on Wed with a better defined wave

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32 minutes ago, StormChaser4Life said:

This thread sure is dead. Lol. I do like the upcoming potential this week. Good moisture and instability though nam is keeping it more into OK and less into KS. A lot of this week, minus a shortwave on Wed, will be mostly mesoscale related details. I'm not a fan of the overall weak wind fields but the chance of discrete development on a sharp dryline is pretty good esp on Wed with a better defined wave

A lot of people are probably doing Mothers Day celebrations. If this thread doesn't heat up Monday and Tuesday I will be shocked though. Discrete development potential in traditional chase territory should get everyone buzzing.

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Hodographs for Wednesday look nasty but 3km CAPE is poor in many of the soundings I’ve been pulling. That’s something to keep an eye on as we get closer 

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39 minutes ago, Snowstorm920 said:

Hodographs for Wednesday look nasty but 3km CAPE is poor in many of the soundings I’ve been pulling. That’s something to keep an eye on as we get closer 

I’m not so sure this will be the case... ample moisture progged by ECMWF/GFS/UKMET/CMC on Wednesday with 65-70 d/Tds common east of the dryline by 21-00z coinciding with 7-7.5 C/km LLVL lapse rates. Low-levels kinematically for this setup are essentially ideal, as are critical angles... my biggest concern is potential for rather weak/marginal 400-200mb winds, which won’t particularly aid in venting of rain out of the updraft. 

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44 minutes ago, jojo762 said:

I’m not so sure this will be the case... ample moisture progged by ECMWF/GFS/UKMET/CMC on Wednesday with 65-70 d/Tds common east of the dryline by 21-00z coinciding with 7-7.5 C/km LLVL lapse rates. Low-levels kinematically for this setup are essentially ideal, as are critical angles... my biggest concern is potential for rather weak/marginal 400-200mb winds, which won’t particularly aid in venting of rain out of the updraft. 

Lack of forcing may hinder development as well. NAM is barely convecting (a known bias) but in this case there are only neutral at best height tendencies across the risk area so it’s at least a bit of a concern. I think we see at least some storms but how many will probably depend on subtle short waves and other small scale features that are hard to predict at range.

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1 hour ago, jojo762 said:

I’m not so sure this will be the case... ample moisture progged by ECMWF/GFS/UKMET/CMC on Wednesday with 65-70 d/Tds common east of the dryline by 21-00z coinciding with 7-7.5 C/km LLVL lapse rates. Low-levels kinematically for this setup are essentially ideal, as are critical angles... my biggest concern is potential for rather weak/marginal 400-200mb winds, which won’t particularly aid in venting of rain out of the updraft. 

The Euro is showing 500mb winds of only 18-35kt winds across many sections of the warm sector, at 18z and 00z. As for severe weather chances, I would certainly hope for global models to predict 0-6km shear values of 40 kt or better. The GFS runs have been showing a corridor of 40 kt shear values, with possible storm motions of only 20 knots in a number of areas.

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Definitely one of those high bust potential but high reward setups. I think there will be dryline supercells but how tornadic I'm not sure. I'm not a fan of the relatively small hodograph size albeit nice curvature. Definitely concerned storms won't be vented enough aloft and that low level shear, speed wise, may not be enough for a robust tornado threat. Obviously if I lived closer I would chase any of these days this week but the target being 8-10+ hrs away I'm not sure it will be worth it for me. May hold off for better setups, hopefully, in the next few weeks. I have a break from classes from the 19th-31st so hope I can chase something meaningful 

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1 hour ago, WhiteoutWX said:

Lack of forcing may hinder development as well. NAM is barely convecting (a known bias) but in this case there are only neutral at best height tendencies across the risk area so it’s at least a bit of a concern. I think we see at least some storms but how many will probably depend on subtle short waves and other small scale features that are hard to predict at range.

What do you make of the NAM’s warm frontal position vs globals. Kind of odd how much different it is... damn near 200+ mile difference.

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27 minutes ago, jojo762 said:

What do you make of the NAM’s warm frontal position vs globals. Kind of odd how much different it is... damn near 200+ mile difference.

Hard to say for sure. It's further south with the cooler air more entrenched into Texas Tuesday night. It has a weaker wave coming out Wednesday as well so probably a combination of those two things. Usually the NAM is best in the winter with shallow cold fronts, but this far into spring it is a little less believable. If we do get a lot of precip Tuesday across the panhandles and OK I could see the cooler airmass being slower to budge than the globals are showing. 

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00z globals continue to show a considerable difference to the NAM... NAM seems to be trending a bit further north with the front, but is still notably a southern outlier. 
 

GFS continues to show what would be a fairly impressive environment in W KS/W OK, looking like an exceptionally chaseable day.

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Still rather large spread in guidance WRT the potential wedge of low theta-e air across KS/OK on Wednesday — presence of such a feature would certainly put a high degree of uncertainty in how exactly the day/risks would evolve.

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NAM has the LLJ screaming across the threat area after sunset Wednesday. Certainly going to be tons of low level shear for storms to work with. Effective bulk shear is still on the low side. Sounding near the OKC area at 03z 

 

EB2E2E4C-D271-4315-BC1F-3927804A1DDC.thumb.png.b09a432d68c9dedecf0cecc66d2aa973.png4059FE01-2C51-492A-AB89-0A3C1532B854.png.d52ad21b03d2de66accc440a631f0a5f.png

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Literally our first or second true dryline day of spring coming up in 48 hours and nobody is talking about it on here... amazing. Wx Twitter seems thoroughly convinced that Wednesday is garbage, I however am certainly not. 
 

Global models continue to indicate a particularly interesting day across OK and KS, NAM is out to lunch imo, at least to an extent... You’ll see the NAM off by 200 miles wrt warm front location before you see the Euro off by that much... several critical things to watch tomorrow, 1. 00z RAOB 850mb temps in SW TX (how strong is the cap going to be along the dryline?), 2. Temperatures/dewpoints tomorrow in SW OK... NAM says mid/upper 40s dewpoints in SW OK, other models say 60s dewpoints.

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If the GFS is really right then we could see dew points of 66F into southwest Kansas, with soundings very supportive of tornadoes, with, thankfully effective wind shear of 33 knots. Overall, I'd like to see shear values over 40 knots for stronger updrafts, but maybe the CAPE and SRH can work together for a reasonable chance at high-end hail and tornadoes. The NAM thinks Kansas will have cold temperatures and an inversion, but has better SRH and effective shear for central Oklahoma. The NAM is kind of weird. I keep thinking that it will eventually flop and have 2000-3000 J/kg of CAPE in Kansas. For several runs, the Euro model has had convection from central to SW Oklahoma and down into central Texas around Brady and San Saba. So that might be something to consider. Obviously the southern areas will have lower shear.

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1 hour ago, jojo762 said:

Literally our first or second true dryline day of spring coming up in 48 hours and nobody is talking about it on here... amazing. Wx Twitter seems thoroughly convinced that Wednesday is garbage, I however am certainly not. 
 

Global models continue to indicate a particularly interesting day across OK and KS, NAM is out to lunch imo, at least to an extent... You’ll see the NAM off by 200 miles wrt warm front location before you see the Euro off by that much... several critical things to watch tomorrow, 1. 00z RAOB 850mb temps in SW TX (how strong is the cap going to be along the dryline?), 2. Temperatures/dewpoints tomorrow in SW OK... NAM says mid/upper 40s dewpoints in SW OK, other models say 60s dewpoints.

Meh. It's 2020 and that itself is a kiss of death for multiple reason. I just had to walk in a sweater and pants in Norman... 48 hours before a potential chase. If it can bust it'll find a way. My 'chasecation' starts Wednesday too. That being said, I'm much more 'in love' with these setups versus the synoptically-evident events. More fun to chase, slower storm motions, and hopefully a few less idiots out and about. Hopefully a fun Texas Panhandle chase will be in order on Wednesday. I'll take this cooler weather over mid 70 degree dewpoints and a ridge. Northwest Texas does seem to be a hot spot this month. 

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00z CAMs largely struggled to sustain convection along the dryline, not too surprising given that they do not necessarily do the best in weakly forced environments. Most solutions do not agree with the NAM’s idea of a strong theta-e gradient along the KS/OK border, aside from the NSSL-WRF.

Not a whole lot to say besides if supercells do go up along the dryline, they’ll probably be fairly intense given strong cape/low-level shear and able to sustain for several hours given ample moisture advection and orthogonal shear vectors.

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SPC goes ENH risk for new Day 2... but for wind.  sig hail contour remains quite large though

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day2otlk_0600.gif

Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1253 AM CDT Tue May 12 2020

   Valid 131200Z - 141200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS
   SOUTHWEST OK AND FAR NORTHWEST TX...

   ...SUMMARY...
   Severe thunderstorms are expected across portions of the central and
   southern Plains Wednesday afternoon through Wednesday night.

   ...Southern/Central Plains...
   Cool and dry continental air mass will stretch from the northern
   High Plains eastward into the Southeast States with its southwestern
   periphery over the central Plains. Strong air-mass modification that
   began on Tuesday will continue Wednesday with low-level moisture
   surging northward into the central Plains. The strongest moisture
   advection (and resulting air-mass modification) will occur over the
   southern Plains and into eastern KS. Much of northern OK and eastern
   KS will likely begin the day with temperatures and dewpoints in the
   upper 40s to mid 50s. However, by early Wednesday afternoon, the
   expectation is for mid 60s dewpoints and temperatures in the mid to
   upper 70s to be near the KS/OK border. Strong frontal wedge will
   likely remain in place across much of western and central KS until
   late Wednesday afternoon. 

   The surface pattern Wednesday afternoon is forecast to consist of a
   low over southeast CO with a dryline arcing southeastward into
   southwest KS and then back southwestward through TX Permian Basin.
   Convective initiation is anticipated along this dryline, with
   forcing for ascent augmented by a weak shortwave trough expected to
   move through the southern High Plains during the afternoon/evening.

   Thermodynamic profiles ahead of the dryline will be characterized by
   a moist but well-mixed boundary layer beneath a well-developed EML
   with 700-500 mb lapse rates near 9 deg C per KM. The result is a
   strongly unstable environment with MLCAPE likely from 2500 to 3000
   J/kg. Kinematic profiles will likely show moderate low-level
   directional shear but relatively weak mid-level flow. This type of
   environment is expected to favor strong/severe storms with robust
   downdrafts, with the weak mid-level flow precluding strong enough
   deep-layer vertical shear for healthy mid-level rotation. Given the
   strong instability, initial development will be intense enough to
   produce large hail (some very large) before then transitioning to
   one or more linear segments. Cold-pool amalgamation could result in
   a strong convective line which may then move into portions of
   central OK and north-central/central TX. Tornado threat will likely
   be limited by the quick linear transition, but given the strong
   buoyancy and favorable low-level shear, a few are still possible.

   Later Wednesday night, elevated thunderstorms are expected to
   develop over north-central/northeast KS and adjacent portions of
   southeast NE, southwest IA, and northwest MO north of the warm front
   Wednesday night, as the low-level jet strengthens and low-level
   moisture continues to surge northward. Hail will be the primary
   severe threat with these storms.

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One of the key factors to consider tomorrow is deep layer shear. Sure, instability will be there and critical angles look good (favorable turning with height), but 30 knots of shear is very marginal/borderline. 

12z 3km NAM shows only 25-30kt deep layer shear along the dryline at CI time. HRRR is not much better at around 30kt.

Sure, you could get a storm or two to take on supercellular characteristics, initially, but a rapid transition to messy/clustered storm modes looks likely. 

Edit to add graphical support:

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Yeah I was really looking forward to a potential chase in my favorite area tomorrow but that hope is fading as im not sure I wanna drive 8 hours just to run from a squall line.  Latest data all showing pretty quick upscale growth. Maybe late May or June will throw us a bone.

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SPC now saying deep layer shear will be in the 40 to 50 kt range with supercells likely with very large hail and a few tornadoes possible in the more dominant and intense sups... this is in the new Day 1 outlook for today 

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Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1229 AM CDT Wed May 13 2020

   Valid 131200Z - 141200Z

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

   ...SUMMARY...
   Isolated to scattered severe thunderstorms are expected across parts
   of the southern and central Plains this afternoon through tonight.
   The greatest threat for numerous severe wind gusts and perhaps some
   very large hail will be across parts of west Texas and western
   Oklahoma.

   ...Southern Plains...
   West to southwest mid-level flow will be in place today across the
   western half of the nation as a shortwave trough moves through the
   flow into the southern High Plains. At the surface, a low will
   deepen in eastern Colorado as a surface trough and dryline become
   more focused in the southern High Plains. A moist airmass will
   advect northward from the lower Rolling Plains into the southeast
   Texas Panhandle this afternoon where surface dewpoints appear likely
   to reach the lower 60s F. As surface heating takes place, moderate
   instability will develop to the east of the dryline from west Texas
   into the eastern Texas Panhandle and eastward across much of the Red
   River Valley. The shortwave trough is timed to reach the dryline in
   the late afternoon, which combined with increasing low-level
   convergence, should result in scattered convective initiation from
   near Amarillo northeastward into the northeastern Texas Panhandle.
   These storms will move eastward into the enhanced risk area during
   the late afternoon and early evening. Additional thunderstorms will
   develop south-southwestward across west Texas during the late
   afternoon.

   RAP forecast soundings to the east of the dryline by late afternoon
   show nearly dry adiabatic lapse rates below 700 mb with MLCAPE in
   the 2000 to 3000 J/kg range. This combined with 0-6 km shear of 40
   to 50 kt will be favorable for supercells with large hail.
   Hailstones greater than 2 inches in diameter will be possible with
   supercells that develop intense cores, from western Oklahoma and the
   eastern Texas Panhandle south-southwestward into the Pecos River
   Valley. As cell coverage increases during the late afternoon and
   early evening, it appears a broken line segment will organize and
   move eastward into western Oklahoma and northwest Texas. Wind damage
   will be likely along the leading edge of the line segment. A few
   tornadoes will be possible with the more dominant supercells as
   well. The enhanced risk area has been adjusted to account for a
   further west position of the dryline.

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It does appear like the models have upped the effective bulk shear closer to the 40 kt range, but the cap is stout ahead of the dryline, especially on the NAM.  Storms may struggle to sustain updrafts long enough to achieve supercellular status. The NAM is also advertising low-level wind fields which are basically unidirectional in the first kilometer by 00z this evening. Combined with models suggesting quick upscale growth, I'm a little skeptical on tornado potential. 

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Headed out to NW OK today... Might not be worth the five hour drive... but liking the dryline bulge/punch w/ 50kt jet core traversing the dryline ~21z in the OK PH, so we’ll see what happens. 

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13 minutes ago, jojo762 said:

Headed out to NW OK today... Might not be worth the five hour drive... but liking the dryline bulge/punch w/ 50kt jet core traversing the dryline ~21z in the OK PH, so we’ll see what happens. 

Probably your best bet today. Will be interesting to see how quickly moisture returns and how long the clouds hang on today. Currently pretty socked in with clouds and fog all across the area. 

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