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May 25th Severe weather thread


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If I were chasing tomorrow I'd head for the Springfield/St. Louis/Quincy triangle, or somewhere west or southwest of Springfield. That's great chase country too. Obviously things may need tweaked by then, but that area should become pretty unstable, and have very respectable deep layer shear. Especially the lower few km.:guitar:

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Good stuff. It's hard to get 850mb winds that backed in Illinois without the mid levels also being backed lol.

I'm pretty impressed with the broad H7 jet punching northeast into the instability axis. Quite a wide area over 50kts, with even some pockets over 60kts. Nice.

storm motion could be a bit of a problem though so a nice right mover would be nice.

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NAM and SPC WRF both hinting at a potential "surprise" up in the Chicago metro late morning and early afternoon with the first wave. The NAM builds instability along the frontal axis ahead of the wave and both models intensify convection around 15z, with the WRF looking like it would paint semi discrete structures with high updraft helicity.

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HRRR up to noontime now. Looks like things are about to explode over eastern Missouri at this point. HRRR forecasts cape values of over 3000j/kg from Quincy/Lincoln southward.

Kind of looks like a snowstorm in western Iowa.

Its also having storms starting to go up in central IL along and south of the warm front..

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NAM and SPC WRF both hinting at a potential "surprise" up in the Chicago metro late morning and early afternoon with the first wave. The NAM builds instability along the frontal axis ahead of the wave and both models intensify convection around 15z, with the WRF looking like it would paint semi discrete structures with high updraft helicity.

thoughts on the mid-afternoon to evening timeframe?

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I personally would only go moderate until evolution of convection/clearing becomes more certain.

I'm curious what you think for further south, down into the Mid-South, down to around the Memphis metro. My thinking is that the best dynamics would go north, but Memphis can still have a strong evening threat, with a possible daytime threat depending on mesoscale factors. What is your thinking on this?

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It looks like there'll be two main focii for initiation, the first being along the cold front across central MO to north-central AR, and the second being along a prefrontal trough near the reintensifying low-level jet along the MS river. The latter I think bears the best chance of significant tornadic supercells given the stronger mid-upper level flow and the stronger LLJ. I would say the area of highest risk would be NW TN/W KY/S IL/SW IN.

I'm buying the NAM depiction of the surface wind field a lot more than the jumbled mess the GFS shows. The NAM shows substantially-backed surface winds ahead of the prefrontal trough, and I suspect that this will play out, and if anything is slightly underestimated.

Overall, I'd probably lean towards this being a high risk eventually, although I'd be on the fence regarding a 06z upgrade as well. This certainly does seem a notch below today's event, though.

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Overall, I'd probably lean towards this being a high risk eventually, although I'd be on the fence regarding a 06z upgrade as well. This certainly does seem a notch below today's event, though.

For sure, meteorologically speaking. But the impact may be worse since there's denser populations on average.

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For sure, meteorologically speaking. But the impact may be worse since there's denser populations on average.

Thats my biggest worry as well.

This map is 5 years old, but still paints the picture well:

us-population-map.gif

Much more red from mississippi river eastward, compared to OK.

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DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1257 AM CDT WED MAY 25 2011

VALID 251200Z - 261200Z

...THERE IS A MDT RISK OF SVR TSTMS ACROSS EASTERN

MISSOURI...EASTERN ARKANSAS...NORTHWEST MISSISSIPPI...WESTERN

TENNESSEE...WESTERN KENTUCKY...CENTRAL AND SOUTHERN ILLINOIS...AND

CENTRAL AND SOUTHERN INDIANA...

...THERE IS A SLGT RISK OF SVR TSTMS EXTENDING FROM THE LOWER GREAT

LAKES REGION WWD ACROSS THE MIDWEST/OH VALLEY AND SWWD INTO AR/NERN

TX/NRN LA...

...SYNOPSIS...

A LARGE UPPER LOW OVER THE CENTRAL PLAINS AT THE START OF THE PERIOD

IS PROGGED TO SHIFT STEADILY EWD WHILE WEAKENING SLOWLY WITH TIME.

THIS LOW SHOULD REACH THE MID MS VALLEY LATE...AS THE MID-LEVEL JET

ROTATES NEWD FROM THE BASE OF THE TROUGH INTO THE TN/OH VALLEYS

THROUGH THE END OF THE PERIOD.

FARTHER WEST...A LOW OVER THE ERN PACIFIC IS FORECAST TO MOVE

ONSHORE...AND WILL WEAKEN AS IT PROGRESSES ACROSS THE PAC NW THROUGH

THE PERIOD.

AT THE SURFACE...A DEEP LOW INITIALLY OVER ERN KS IS EXPECTED TO

REACH NRN INDIANA LATE...WITH A TRAILING COLD FRONT TO LIKEWISE

ADVANCE EWD ACROSS MO/AR TOWARD THE OH VALLEY. IN THE WEST...A COLD

FRONT AHEAD OF THE UPPER SYSTEM MOVING ONSHORE WILL CROSS THE PAC NW

AND THE GREAT BASIN THROUGH 26/12Z.

...LOWER GREAT LAKES/OH VALLEY WWD INTO SERN IA/MO/AR/LA/E TX...

A BROAD ZONE OF POTENTIALLY SIGNIFICANT SEVERE WEATHER -- INCLUDING

VERY LARGE HAIL...WIDESPREAD DAMAGING WINDS...AND SCATTERED

STRONG/DAMAGING TORNADOES -- IS FORECAST ACROSS A REGION CENTERED

OVER THE MID MS/OH/TN VALLEYS TODAY.

AT THE START OF THE PERIOD...GENERALLY SUB-SEVERE STORMS SHOULD BE

CROSSING IA/IL...WITH ISOLATED/WEAKENING CONVECTION POSSIBLY ARCING

SWD ACROSS THE MID MS VALLEY AND THEN SWWD INTO ERN TX.

AS THE CONVECTION MOVES INTO THE SRN UPPER GREAT LAKES REGION AND

ACROSS THE OH VALLEY STATES THROUGH MIDDAY...HEATING/DESTABILIZATION

OF THE PRE-CONVECTIVE AIRMASS SHOULD PERMIT

REINTENSIFICATION/EXPANSION OF STORMS ACROSS THIS REGION. STORM

EXPANSION MAY POSSIBLY EXTEND AS FAR S AS WRN TN/NRN MS.

MEANWHILE...STORM DEVELOPMENT IS FORECAST TO OCCUR BY EARLY

AFTERNOON IN A SECOND BAND FARTHER W...DEVELOPING ACROSS MO JUST

AHEAD OF THE UPPER SYSTEM...AND THEN EXPANDING SWD ALONG THE SURFACE

FRONT. WITH A VERY MOIST WARM SECTOR AIRMASS...STRONG INSTABILITY

IS EXPECTED TO DEVELOP BY AFTERNOON. WITH 70 KT MID-LEVEL SWLY JET

ACROSS THE MID MS/LOWER OH VALLEY REGION ON SERN FRINGE OF THE

ASSOCIATED LOW...SHEAR/INSTABILITY COMBINATION WILL FAVOR RAPID

INTENSIFICATION OF STORMS -- WITH STORM MODE TO INCLUDE BOTH

SUPERCELLS...AND RAPIDLY MOVING/BOWING CLUSTERS. IN ADDITION TO

STRONG MID-LEVEL MESOCYCLONES... LOW-TROPOSPHERIC SHEAR WILL ALSO

SUPPORT LOW-LEVEL ROTATION...AND THEREFORE POTENTIAL EXISTS FOR

SEVERAL LARGE/STRONG TORNADOES. DAMAGING WINDS ARE LIKEWISE

EXPECTED -- PARTICULARLY NEAR BOWING STORM CLUSTERS...AND LARGE HAIL

IS ALSO LIKELY ACROSS THIS REGION.

THE SECOND/FRONTAL BAND OF STORMS SHOULD CROSS THE MS VALLEY INTO

EARLY EVENING...WITH SEVERE POTENTIAL ADVANCING ACROSS THE OH AND TN

VALLEY REGIONS THROUGH LATE EVENING. GRADUAL DECREASE IN STORM

SEVERITY IS EXPECTED OVERNIGHT...BUT LIMITED SEVERE THREAT MAY

APPROACH THE WRN SLOPES OF THE APPALACHIANS -- AND SHIFT SWD TOWARD

THE CENTRAL GULF COAST -- THROUGH THE END OF THE PERIOD.

..GOSS.. 05/25/2011

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You know it's going to be a rough severe weather day when the NWS is using the SPS to get severe weather safety information out.

You got that right. Im curious as to how much the early stuff affects our heating and instability. I just cant get a good feel for this event right now. Not sure how its going to pan out.

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