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April 14-17th Severe Weather (Day 3 Mod)

Chicago Storm

By Chicago Storm,
in Central/Western States

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tornadotony

tornadotony

Posted
Posted

Get the shoe ready.  Salt it, please.

 

There is one thing that is becoming abundantly clear about tomorrow and tomorrow night that will probably make everything I've said to this point moot.  The boundary layer is not going to decouple from the sfc tomorrow evening as per normal.  With the high humidity and intense low-level shear-induced mechanical turbulence, this is the reality.  Some of the overnight soundings have already been posted and I'm not about to beat that dead horse.

 

Given this, significant severe weather is likely to occur across Oklahoma and Texas.  That is something I really don't doubt anymore.  Storm mode is still a question.  If we see a warm frontal location/orientation like that of the NAM, we will likely see some upscale growth of a complex during the evening.  If we see the warm front push farther N, we'll see more discrete activity across OK and a major tornado outbreak will be likely.  Here's another catch, though.  Even the NAM reorients the boundary N/S overnight, with the southern part of the front accelerating in response to cyclogenesis on the eastern Plains.  If this happens, then even a QLCS would likely have embedded supercells and a significant tornado threat.

 

One potential caveat is midday convection.  The NAM generates an MCS around midday, and the Euro generates some convection that looks less organized.  Either way, I don't think this hinders the threat too much either way.  With such high levels of humidity and strong low-level flow, I think that even a cold pool from an MCS could be sufficiently modified for an evening/overnight threat.

 

Farther north, a sleeper play tomorrow is the warm front across NE MO and central IL.  Weak-mdt instability will be in place along the front, along with large, looping hodographs.  After dark, the NAM and GFS show slight sfc stabilization, but with 50kt winds at 925mb, I would not rule out a tornado threat continuing during the overnight hours, and, depending on the progress of the warm front, maybe even approaching Chicago by 09z or so.  A hail threat seems like a foregone conclusion.

 

Then comes the fun on Thursday.  This is going to be a very complex scenario that may result in some areas seeing a prolonged, multiple-round significant severe weather episode.  The NAM, GFS, and Euro are actually in pretty good agreement about the evolution of convective activity on Thursday.  After clearing out the original convection from IL/IN around 12z, another round of convection develops near the MS River and moves across nrn IL, nrn IN, and srn MI between about 15z to the west and 21z to the east.  Ahead of that convection, CAPE exceeds 1000J/kg+ and 0-1km SRH of 200-300 m^2/s^2, with 0-6km shear of 45-60kt suggests that, at a minimum, semi-discrete supercell structures with a strong tornado threat are possible, even with this round of convection, despite the timing.  And if that weren't enough, the GFS, Euro, and NAM recover the atmosphere immediately behind that round of convection and provide and environment for a significant QLCS with a wind and tornado threat to develop along the cold front around 21z and push across IL and IN.

 

Farther south, the QLCS will continue down the front into AR and eventually push east across TN, KY, MS, and AL through the overnight hours Thursday night/Friday morning.  There is some indication that more discrete convection could form ahead of the front giving an lack of capping over the warm sector.  Once again, with the amount of boundary layer humidity and the strength of the low-level wind fields, wind and tornadoes will be possible with the QLCS, with that threat lasting overnight across the OH and TN Valleys.

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brettjrob

brettjrob

Posted
Posted

HRRR is surprisingly aggressive compared to even the RAP through late morning. While the northern solutions that lift beyond the KS border can likely be discarded, I'm still completely stumped in the range between the NAM (near I-44) and something more like what extrapolation of this HRRR image would imply. And within that range are major differences in the scope of the threat, though the general area around LAW/SPS looks pretty primed either way.

 

post-972-0-07671600-1366177031_thumb.png

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patrick7032

patrick7032

Posted
Posted

FWIW...based on current obs...the NAM sfc forecast temp/winds at 00z initialization are pretty close to the current sfc obs. I agree with baro and others about the NAM "blue norther" plunge in western Oklahoma is unlikely. Many mets at our office stated earlier today that it was against climo and without a good arctic high push it was likely a bad forecast on the NAM's part. That said...believe the NAM frontal position is pretty close...maybe just a little far se. Using a model "blend" and ignoring the sfc front forecast from the GFS...I don't know about everyone else...but I think the front will largely parallel I-44 but roughly 50-80 miles northwest...or on a line from just north of Childress to just nw of OKC to ESE of ICT...paralleling I-35 in Kansas or just se of there. Just my "best guess".

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wxmeddler

wxmeddler

Posted
Posted

FWIW...based on current obs...the nam sfc forecast temp/winds at 00z initialization are pretty close to the current sfc obs. I agree with baro and others about the nam "blue norther" plunge in western Oklahoma is unlikely. Many mets at our office stated earlier today that it was against climo and without a good artic high push it was likely a bad forecast on tha NAM's part. That said...believe the NAM frontal position is pretty close...maybe just a little far se. Using a model "blend" and ignoring the sfc front forecast from the GFS...I don't know about everone else...but I think the front will largely parrel I-44 but roughly 50-80 miles northwest...or on a line from just north of Childress to just nw of OKC to ESE of ICT...paralleling I-35 in Kansas or just se of there. Just my "best guess".

 

I think this is right on. Looking at the latest RAP runs... all the ingredients for a major outbreak in the works for the I-44 corridor and also near the WF in MO,IL and into W IN.

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thewxmann

thewxmann

Posted
Posted

HRRR is surprisingly aggressive compared to even the RAP through late morning. While the northern solutions that lift beyond the KS border can likely be discarded, I'm still completely stumped in the range between the NAM (near I-44) and something more like what extrapolation of this HRRR image would imply. And within that range are major differences in the scope of the threat, though the general area around LAW/SPS looks pretty primed either way.

 

 

12Z ECMWF takes the front to the KS/OK border at 18Z before it begins to crash south.

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brettjrob

brettjrob

Posted
Posted

I think this is right on. Looking at the latest RAP runs... all the ingredients for a major outbreak in the works for the I-44 corridor and also near the WF in MO,IL and into W IN.

 

I also agree with his thinking on frontal position as a best guess. If it pans out, this should expose enough of the warm sector to high-end shear for a significant to borderline-major event.

 

12Z ECMWF takes the front to the KS/OK border at 18Z before it begins to crash south.

 

I'd be surprised if it makes it that far N at all, though I wouldn't rule it out yet (am ruling out I-70, though). I also doubt it will come "crashing" until 3z-6z.

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LocoAko

LocoAko

Posted
Posted

..SOUTHERN PLAINS TO LOWER MO VALLEY/MIDWEST  
 
WELL-ABOVE TYPICAL GUIDANCE SPREAD CONTINUES INTO THE DAY 1  
PERIOD...ACCENTUATED BY A MUCH MORE NORTHWARD AND SEEMINGLY LESS  
LIKELY SOLUTION OF THE 00Z GFS AS COMPARED TO THE 00Z NAM/12Z ECMWF.  
AMONG OTHER UNCERTAINTIES...THIS IS A FACTOR FOR ONLY MODEST  
CONFIDENCE IN SPECIFIC DETAILS LATER TODAY. EVEN SO...POTENTIALLY  
WIDESPREAD/MULTI-FACETED SEVERE WEATHER IS LIKELY ESPECIALLY INTO  
THIS AFTERNOON/EVENING.  
 
INITIALLY...ELEVATED STRONG/POTENTIALLY SEVERE TSTMS CAPABLE OF HAIL  
WILL LIKELY BE ONGOING THIS MORNING ACROSS PORTIONS OF THE  
LOWER/MIDDLE MO VALLEY AND ADJACENT MIDWEST. THIS WILL BE IN  
ASSOCIATION WITH A STRONG LOW LEVEL JET/WARM ADVECTION REGIME.  
 
FARTHER SOUTH...A MORE WIDESPREAD/SURFACE BASED TSTM THREAT WILL  
LIKELY EVOLVE AS EARLY AS THIS AFTERNOON...BUT ESPECIALLY INTO THIS  
EVENING/TONIGHT ACROSS THE SOUTHERN PLAINS TO THE LOWER MO VALLEY IN  
GENERAL VICINITY OF AFOREMENTIONED FRONTAL ZONE. WHILE NOT  
NECESSARILY LIKELY...THERE MAY BE SOME POSSIBILITY THAT TSTMS  
DEVELOP RELATIVELY EARLY IN THE AFTERNOON ACROSS PORTIONS OF NORTH  
TX INTO EASTERN OK AND PERHAPS EVEN THE OZARKS...AND POTENTIALLY  
BECOME SURFACE BASED WITHIN AN INCREASINGLY MOIST/UNINHIBITED  
BOUNDARY LAYER. SHOULD THIS OCCUR...DISCRETE SUPERCELLS CAPABLE OF  
LARGE HAIL/TORNADOES WOULD BE POSSIBLE.  
 
SURFACE BASED DEVELOPMENT DOES SEEM MORE PROBABLE NEAR THE TRIPLE  
POINT VICINITY OF DRYLINE/COMPOSITE FRONT...UNDER THE INFLUENCE OF A  
BIT STRONGER HEATING/MASS CONVERGENCE. THIS WOULD BE ACROSS PARTS OF  
NORTH-CENTRAL/NORTHWEST TX INTO SOUTHWEST/SOUTH-CENTRAL OK.  
ESPECIALLY GIVEN AN INTENSIFYING LOW LEVEL JET TOWARD/AFTER  
DARK...POTENTIAL WOULD EXIST FOR LARGE HAIL AND PERHAPS A FEW STRONG  
TORNADOES ACROSS THIS REGION.  
 
OTHERWISE...STORMS ARE EXPECTED TO INCREASE AFTER DARK IN VICINITY  
OF THE SOUTH-SOUTHWEST TO NORTH-NORTHEAST ORIENTED FRONTAL ZONE  
ACROSS OK INTO THE LOWER MO VALLEY AND EVENTUALLY MIDDLE MS VALLEY  
MIDWEST. SOME POTENTIAL FOR SURFACE BASED TSTMS/SUPERCELLS AND  
ASSOCIATED DAMAGING WIND/TORNADO POTENTIAL WILL EXIST MAINLY THROUGH  
THE EVENING IMMEDIATELY NEAR THE FRONT...BUT THERE WILL LIKELY BE A  
TENDENCY FOR UPDRAFTS TO BE UNDERCUT BY THE NOCTURNALLY  
SOUTH/SOUTHEASTWARD-ACCELERATING COLD FRONT. AS SUCH...LARGE HAIL  
MAY BECOME THE MOST PROBABLE/MORE WIDESPREAD CONCERN ACROSS THE  
REGION.  

 

 

Edited to add: went 15% hatched tor in SW OK, 30% wind, and hail 45% hatched across OK. 

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andyhb

andyhb

Posted
Posted

I think this is right on. Looking at the latest RAP runs... all the ingredients for a major outbreak in the works for the I-44 corridor and also near the WF in MO,IL and into W IN.

 

Looking at the RAP instability parameters, once that LLJ fires up tomorrow, both the southern and northern threats, like you mentioned, could really take off.

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andyhb

andyhb

Posted
Posted

00z ECMWF came well south, looks actually a lot like the Rap. Didn't realize the ECMWF wunderground CAPE works...but it has 2700+ across SW Oklahoma by 21z...not sure if it is SBCAPE/ML/MU though.

 

SW OK and the Wichita Falls area just looks deadly on the Euro by 00z. 2500-3000+ J/kg of CAPE pooling near the dryline and sfc winds backing fairly strongly (LLJ strength increasing of course as well).

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brettjrob

brettjrob

Posted
Posted

SW OK and the Wichita Falls area just looks deadly on the Euro by 00z. 2500-3000+ J/kg of CAPE pooling near the dryline and sfc winds backing fairly strongly (LLJ strength increasing of course as well).

 

Yeah, there's really not much more that can be said about that environment. Such a focused, but sky-high, tornado threat as progged.

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baroclinic_instability

baroclinic_instability

Posted
Posted

SW OK and the Wichita Falls area just looks deadly on the Euro by 00z. 2500-3000+ J/kg of CAPE pooling near the dryline and sfc winds backing fairly strongly (LLJ strength increasing of course as well).

The 00z ECMWF verbatim is ugly....it does look like a lot of guidance has a slight cold pool farther E towards Lawton. The SPC outlook generally matches the 00z EC quite well. 

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