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Mar. 27-31 Severe Threats


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I think while not specifically mentioning it, the primary reasoning was concern for things getting too messy with no capping and storm mergers/interference, as well as poor directional shear. This is basically what did in the Kansas potential today. With such impressive speed shear/kinematics you can't rule out a more substantial event, but for the LOT CWA specifically I wouldn't be shocked if there were only a few severe reports.

We're in St. Louis for the night and have to decide whether to gamble over IL/IN that something will produce or head south to where the better potential appears to be.

 

Thanks for chiming in.  Since you brought up Kansas, would point out that the deep layer flow/speed shear in our area looks better than it did out there. 

 

The veered boundary layer flow isn't something that suddenly popped up, so was just surprised to see the ENH removed from IL/IN.  Would've actually understood it more if there hadn't been that ENH area to begin with.

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Thanks for chiming in. Since you brought up Kansas, would point out that the deep layer flow/speed shear in our area looks better than it did out there.

The veered boundary layer flow isn't something that suddenly popped up, so was just surprised to see the ENH removed from IL/IN. Would've actually understood it more if there hadn't been that ENH area to begin with.

That's a very good point about the speed shear being much stronger being right under the H5 jet. I think I came across as too pessimistic almost with my first response- you can easily envision a way in which there are fairly widespread reports. It just gives me pause with strong forcing, little capping, and early initiation and the high res guidance really lighting up with convection, which is probably not a good thing in terms of getting dominant cell (s) to produce higher end severe weather.

It's also a good point about the removal of the ENH on the first day 1 outlook. It demonstrates subjecitivty forecaster to forecaster with these outlooks when it could have been valid to be more conservative and at least wait til 13z for instance. I do think that it probably at least partially came down to the outlook forecaster assessing things, deciding that the southern target had a higher threat level than farther north but not wanting to designate any MDT areas, so as a result wasn't comfortable having the two areas in the same categorical risk level.

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59/56 here with the low level flow ramping up here. 60% chance of storms tomorrow in my grid forecast. Have already had a couple nice rumblers tonight.

 

EURO showing a moderate risk of severe weather from roughly Champaign to GRR around 18z. Showing some convective elements in NE IL as well.

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I was wondering about that - how this morning's precip was going to affect atmospheric recovery to allow for convection later...  

 

 

I think the closer temps get to 70, the better.  May be optimistic for northern IL/IN to reach that but any sun should allow for a quick spike.

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Watching that cluster in N AR as HRRR has it coming up the Ohio River. ILN said something about this in their mid-morning AFD update

 

SEVERE WEATHER POTENTIAL -- BIG KEY IS WHETHER SUNSHINE CAN BREAK
OUT OR NOT AND INDUCE DESTABILIZATION AT A QUICKER RATE THAN SEEN
RIGHT NOW IN GUIDANCE. RIGHT NOW...NWP FCST SOUNDINGS NOT SHOWING
MUCH CHANCE FOR A LOT OF SUNSHINE WHICH KEEPS AFTN DESTABILIZATION
FROM GETTING OUT HAND...INSTEAD FOCUSING BEST BUILD OF CAPE BACK
ALONG COLD FRONT IN WRN IND. IN COMPARISON TO DATA
YESTERDAY...SEEMS MODELS HAVE TRENDED TO LESS DESTABILIZATION.
HOWEVER...CONTINUED WAA AS VEERING SWLY BOUNDARY LAYER FLOW AS LOW
DEEPENS AND MOVES INTO LOWER MICHIGAN WILL COMBINE WITH DWPTS IN
THE UPPER 50S TO AROUND 60 TO PROMOTE WEAK MLCAPE AMIDST STRONG
TROPOSPHERIC SHEAR PROFILES /MOSTLY DUE TO SPEED SHEAR AND LESSER
CONTRIBUTIONS FROM DIRECTIONAL SHEAR/. EXPECT STORMS TO FIRE BACK
ALONG COLD FRONT IN WRN IND BY EARLY AFTERNOON AND LIKELY BECOME
SEVERE. SECOND AREA OF CONCERN WILL BE PREFRONTAL CONVERGENCE BAND
OF STORMS THAT MAY FIRE OVER SRN IND INTO KY...RACING NORTHEAST
TOWARD TRI STATE BY EARLY EVENING. THIS CONTINUES TO BE DUPLICATED
OVER MANY RUNS OF EXPERIMENTAL HRRR
...HI-RES WRF WINDOWS...AND SOME NCAR DART MEMBERS. CAMS SHOWING
DISCRETE/SPLITTING CELLS AS STORM MODE IN THE LATTER AREA WHICH
FITS THE LONG/RATHER STRAIGHT HODOGRAPHS SEEN ON FCST SOUNDINGS.
ALSO SEEING DISCRETE STORMS/SPLITS EMANATING FROM WRN INDIANA
ACTION...SO THERE IS SOME CONCERN THAT RIGHT MOVERS MAY PROVIDE
BRIEF TORNADO POTENTIAL PARTICULARLY IN THE TRI STATE PORTION OF
THE CWA BETWEEN 5 PM AND 8 PM IF STORMS CAN DEVELOP AS MENTIONED
ABOVE. HAVE SEEN LOCAL MAXIMUM OF UPDRAFT HELICITY IN THIS AREA
FOR SEVERAL RUNS IN THE 21Z-00Z TIMEFRAME WITH DISCRETE STORM
STRUCTURES IN SIM REF. HAIL WILL BE A THREAT WITH EITHER
DISCRETE/SUPERCELL STRUCTURE. WIND A BETTER THREAT FOR CONGEALED
LINE SEGMENTS COMING OUT OF INDIANA/KY A LITTLE BIT LATER IN THE
EVENING BUT WOULD BE SLOWLY RUNNING OUT OF THE MARGINAL INSTBY
ONCE CROSSING THE OHIO LINE. SO THREAT WINDOW SEEMS TO RESIDE FROM
~4 PM TO ABOUT 9 PM BEFORE SLOW COOLING OF THE BOUNDARY LAYER WILL
FORCE STORMS TO BECOME MORE ELEVATED WITH TIME AND RUNNING AWAY
FROM POSI-TILTED INSTBY GRADIENT WITH SURFACE LOW PULLING AWAY
FROM REGION.

 

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