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April 21-24th Severe Weather


SEMIweather

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12z soundings for OUN and SGF show significant helicity...with OUN 0-1 at 613 m2/s2, 0-3 at 699...and SGF 0-1 at 468 and 0-3 at 519...

With bulk shear between 35 and 50 knots, supercells should be possible, at least with the initial development...I'd anticipate that the moderate risk is out for very large hail, but would not be surprised to see an increase in tornado threat.

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DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1104 AM CDT FRI APR 22 2011

VALID 221630Z - 231200Z

...THERE IS A MDT RISK OF SVR TSTMS LATE THIS AFTERNOON AND EVENING

OVER PORTIONS OF EASTERN OK...NORTHWEST AR...AND SOUTHERN MO...

...THERE IS A SLGT RISK OF SVR TSTMS FROM CENTRAL TX INTO THE MID MS

AND MUCH OF THE OH VALLEY...

A FAST-MOVING UPPER TROUGH OVER THE CENTRAL PLAINS WILL TRACK

EAST-NORTHEASTWARD DURING THIS FORECAST PERIOD INTO THE UPPER

MIDWEST. AS THIS OCCURS...STRONG SOUTH-SOUTHWESTERLY LOW LEVEL

WINDS ACROSS THE PLAINS AND MS VALLEY WILL TRANSPORT GULF MOISTURE

RAPIDLY NORTHWARD AND RESULT IN A RATHER LARGE AREA OF THUNDERSTORM

POTENTIAL. THE GREATEST CONCENTRATION OF SEVERE WEATHER WILL LIKELY

EXTEND FROM OK INTO SOUTHERN MO.

..MO/IL INTO OH VALLEY

A CLUSTER OF INTENSE THUNDERSTORMS IS ONGOING THIS MORNING NEAR THE

STL AREA. THESE STORMS APPEAR TO BE ASSOCIATED WITH WARM ADVECTION

NEAR THE NOSE OF THE LOW LEVEL JET...AND IN REGION OF MODERATE

ELEVATED INSTABILITY. THIS ACTIVITY APPEARS TO BE SUFFICIENTLY

ORGANIZED TO MAINTAIN INTENSITY AND TRACK EASTWARD INTO THE OH

VALLEY DURING THE AFTERNOON AND EVENING. A RETREATING SURFACE WARM

FRONT OVER THE OH VALLEY WILL LIKELY HELP FOCUS THE CONVECTION.

DAMAGING WINDS AND LARGE HAIL ARE THE MAIN THREATS.

..MO/AR/OK/TX

A SURFACE COLD FRONT IS SURGING SOUTHEASTWARD ACROSS NORTHWEST

OK...AND SHOULD EXTEND FROM SOUTHEAST KS INTO CENTRAL OK BY LATE

AFTERNOON. AHEAD OF THE FRONT...SOUTHERLY WINDS HELPING TO ADVECT

MOISTURE NORTHWARD WITH MID 60S DEWPOINTS LIKELY ACROSS THE REGION

LATER TODAY. CONSIDERABLE DAYTIME HEATING WILL WEAKEN THE CAPPING

INVERSION AND HELP THE DEVELOPMENT OF SCATTERED THUNDERSTORMS ALONG

THE FRONT...AND POTENTIALLY MORE DISCRETELY IN THE WARM SECTOR.

FORECAST SOUNDINGS SHOW RATHER LARGE HODOGRAPHS AND STEEP MID LEVEL

LAPSE RATES. THIS SUGGESTS SUPERCELL STORMS ARE LIKELY WITH VERY

LARGE HAIL AND DAMAGING WINDS POSSIBLE. TORNADOES APPEAR OF

GREATEST CONCERN OVER SOUTHERN MO...FAR NORTHERN AR...AND EVENTUALLY

INTO SOUTHERN IL WHERE ENHANCED LOW LEVEL SHEAR NEAR THE RETREATING

WARM FRONT WILL BE PRESENT. STORMS MAY PERSIST THROUGH MUCH OF THE

NIGHT WITH ACTIVITY SPREADING ACROSS THE MID MS AND INTO THE OH

VALLEY.

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I'm concerned about the tornado threat for Nrn AR, Srn MO, and Srn IL this evening.

I was just thinking the same thing too. It is plenty sunny here so we should make it up close to 80, with the dew point is 66. We can only have so many close calls, and we have had several already this year, before something significant happen in along the central/west AR/MO border area.

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AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE TULSA OK

1156 AM CDT FRI APR 22 2011

...UPDATE...

.DISCUSSION...

COLD FRONT CURRENTLY PUSHING INTO FAR WESTERN SECTIONS OF OSAGE/PAWNEE

COUNTIES...EXTENDING SOUTHWEST THROUGH CENTRAL/SOUTHWEST OKLAHOMA

TO JUST EAST OF ALTUS. FRONTAL BOUNDARY EXPECTED TO BE NEAR THE

INTERSTATE 44 CORRIDOR SHORTLY BEFORE 00Z WITH MODERATE TO HIGH

SURFACE BASED INSTABILITY DEVELOPING BY THIS TIME AS STRONG SURFACE

HEATING CONTINUES.

AS UPPER DISTURBANCE MOVES INTO THE SOUTHERN PLAINS...SCATTERED

SEVERE THUNDERSTORMS WILL QUICKLY DEVELOP ALONG THE FRONT BY LATE

AFTERNOON...PUSHING EAST/SOUTHEAST THIS EVENING INTO SOUTHEAST

OKLAHOMA/NORTHWEST ARKANSAS. ALTHOUGH LOW LEVEL WIND FIELDS WILL

REMAIN SOMEWHAT WEAK/VEERED AHEAD OF THE FRONT...ANY DEVIANT STORM

MOTIONS COULD PROVIDE ENOUGH STORM RELATIVE HELICITY TO SUPPORT A

TORNADO THREAT. REGARDLESS...VERY LARGE HAIL/DAMAGING WINDS WILL

BE LIKELY WITH THE MORE DISCRETE SUPERCELLS THAT INITIALLY DEVELOP

THROUGH MID EVENING. THUNDERSTORMS MAY BEGIN TO DECREASE IN

COVERAGE BY LATE EVENING AS WARM 850 MB TEMPERATURES SPREAD ACROSS

WARM SECTOR...WITH CONVECTIVE DEVELOPMENT BECOMING MORE FOCUSED

NORTH OF THE STALLED FRONT OVERNIGHT. SENT UPDATED ZONES TO

REFLECT CURRENT THINKING... INCREASING POPS/SEVERE CHANCES

ALONG/DIRECTLY SOUTH OF INTERSTATE 44. NO OTHER SIGNIFICANT

CHANGES ANTICIPATED ATTM.

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ANY DEVIANT STORM

MOTIONS COULD PROVIDE ENOUGH STORM RELATIVE HELICITY TO SUPPORT A

TORNADO THREAT

Watching the tornado warned storms on both the PC and TWC in WC Texas, and even Jim Cantore noticed, the storms followed mean flow when not tornado warned, ie, SW to NE, but headed due East to even a touch South of due East when Tornado Warned. A formerly tornado warned cell near ABI turned back to a normal direction when it weakened.

I'm wondering how much very low level helicity is required if a storm has enough mid level shear to develop a meso and start heading right and increasing its own SRH...

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18z update

tornado threat continues to rapidily increase over central and southern MO

clearing taking place and maybe a boundary backing winds just south of the true warm front

CU building to the south of kansas city

strong tornados appear possible

STL may just time it right..clear out some later but winds stay backed

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MESOSCALE DISCUSSION 0516

NWS STORM PREDICTION CENTER NORMAN OK

0104 PM CDT FRI APR 22 2011

AREAS AFFECTED...CNTRL/SRN MO

CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY

VALID 221804Z - 222000Z

STORM INITIATION APPEARS LIKELY FROM WCNTRL MO...SSE OF KANSAS CITY

METRO...TO EXTREME SERN KS AFTER 21Z. INITIAL SUPERCELLS WILL

EVOLVE INTO LINE SEGMENTS WITH TORNADOES...VERY LARGE HAIL AND

DAMAGING WINDS ACROSS CNTRL AND SRN MO THROUGH EARLY EVENING.

TORNADO WATCH WILL BE LIKELY /GREATER THAN 80 PERCENT/ BY 21Z.

PLAINS PROFILER AND PRESENCE OF JET STREAK CIRRUS SUGGEST A

MID-LEVEL WAVE AXIS WAS SWINGING THROUGH CNTRL KS AT 18Z. ACCAS

FIELD WAS EXPANDING OVER SE KS/WCNTRL MO...INDICATIVE OF INCREASING

ASCENT AHEAD OF THE WAVE. CONTINUED MOISTENING VIA ASCENT SHOULD

ERODE CAP SUFFICIENTLY FOR SFC-BASED STORM INITIATION ALONG THE COLD

FRONT AFTER 21Z.

PRE-FRONTAL WARM SECTOR WAS RECOVERING RAPIDLY AS CLOUD COVER ERODES

AND BOUNDARY LAYER DEW POINTS SURGE INTO THE MID 60S. EXPECT 8 DEG

C PER KM H7-H5 LAPSE RATES TO RESULT IN VIGOROUS UPDRAFTS WITH 45-50

KTS OF EFFECTIVE SHEAR YIELDING SUPERCELLS WITH INITIAL DEVELOPMENT.

VERY LARGE HAIL IS LIKELY. STRONGEST LOW-LEVEL TURNING WILL EXIST

ACROSS THE CNTRL/ERN OZARKS CLOSER TO THE WARM FRONT...BUT

SUFFICIENT 0-1KM SRH SHOULD EXIST OVER THE ENTIRE REGION FOR A FEW

TORNADOES BEFORE ACTIVITY BECOMES PRIMARILY WIND/HAIL THREATS LATER

THIS EVENING.

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Tornado Watch likely ...

MESOSCALE DISCUSSION 0516

NWS STORM PREDICTION CENTER NORMAN OK

0104 PM CDT FRI APR 22 2011

AREAS AFFECTED...CNTRL/SRN MO

CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY VALID 221804Z - 222000Z

STORM INITIATION APPEARS LIKELY FROM WCNTRL MO...SSE OF KANSAS CITY METRO...TO EXTREME SERN KS AFTER 21Z. INITIAL SUPERCELLS WILL EVOLVE INTO LINE SEGMENTS WITH TORNADOES...VERY LARGE HAIL AND DAMAGING WINDS ACROSS CNTRL AND SRN MO THROUGH EARLY EVENING. TORNADO WATCH WILL BE LIKELY /GREATER THAN 80 PERCENT/ BY 21Z. PLAINS PROFILER AND PRESENCE OF JET STREAK CIRRUS SUGGEST A MID-LEVEL WAVE AXIS WAS SWINGING THROUGH CNTRL KS AT 18Z. ACCAS FIELD WAS EXPANDING OVER SE KS/WCNTRL MO...INDICATIVE OF INCREASING ASCENT AHEAD OF THE WAVE. CONTINUED MOISTENING VIA ASCENT SHOULD ERODE CAP SUFFICIENTLY FOR SFC-BASED STORM INITIATION ALONG THE COLD FRONT AFTER 21Z. PRE-FRONTAL WARM SECTOR WAS RECOVERING RAPIDLY AS CLOUD COVER ERODES AND BOUNDARY LAYER DEW POINTS SURGE INTO THE MID 60S. EXPECT 8 DEG C PER KM H7-H5 LAPSE RATES TO RESULT IN VIGOROUS UPDRAFTS WITH 45-50 KTS OF EFFECTIVE SHEAR YIELDING SUPERCELLS WITH INITIAL DEVELOPMENT. VERY LARGE HAIL IS LIKELY. STRONGEST LOW-LEVEL TURNING WILL EXIST ACROSS THE CNTRL/ERN OZARKS CLOSER TO THE WARM FRONT...BUT SUFFICIENT 0-1KM SRH SHOULD EXIST OVER THE ENTIRE REGION FOR A FEW TORNADOES BEFORE ACTIVITY BECOMES PRIMARILY WIND/HAIL THREATS LATER THIS EVENING. ..RACY.. 04/22/2011

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19z update

latest trends and RUC confirm moderate risk needs expanded into southern IL and surrounding areas..i would also hatch the tornadoes over eastern MO and S IL

warm sector will expand north this afternoon with low-mid 70 temps and mid 60's dewpoints and winds should stay backed in these areas...LLj will incease to 60kts this evening

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From Springfield MO, MCD

THE CAP WILL LIKELY

LIMIT CONVECTION ACROSS THE AREA EARLY THIS AFTERNOON...BUT AFTER

21Z (4 PM CDT) THE CAP SHOULD BEGIN TO WEAKEN ENOUGH FOR STORMS TO

DEVELOP ALONG THE FRONT. AS THE CAP WEAKENS ENOUGH FOR STORMS TO

DEVELOP...EXPECT RAPID DEVELOPMENT AS STEEP LAPSE RATES AND AN

UNSTABLE AIRMASS WILL BE IN PLACE.

WIND FIELDS SUGGEST THAT STORMS WILL BE ABLE TO MOVE OFF THE

FRONT...WITH DISCRETE CELLS OR LINE SEGMENTS EXPECTED TO INITIALLY

DEVELOP ALONG THE FRONT. THE VERY STEEP LAPSE RATES AND SIGNIFICANT

CAPE IN THE HAIL GROWTH ZONE WILL SUPPORT THE POTENTIAL FOR VERY

LARGE HAIL...UP TO BASEBALL IN SIZE. THERE WILL BE THE POTENTIAL FOR

A FEW TORNADOES...AS THE VERY STRONG LOW LEVEL WIND SHEAR WILL BE IN

PLACE. SURFACE WINDS WILL BE VEERED HOWEVER...WHICH MAY LIMIT THE

POTENTIAL SOME...WITH LARGE HAIL THE PRIMARY RISK. HOWEVER...AGAIN

WITH THE SUPERCELLUAR STORM MODE AND STRONG WIND SHEAR THE POTENTIAL

STILL EXPECTS...ESPECIALLY ACROSS SOUTHERN MISSOURI.

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HRRR is trending best storms increasingly farther S into N Texas with each run, this morning they looked E of Ardmore, now S of the Red River, FWIW.

I'm about five miles south of Ardmore now on I-35. Small CU field with nothing impressive as of yet. The HRRR performed poorly yesterday so I'm trying to use it cautiously, but I'm definitely watching that trend in case I need to head south. FWIW my live stream is up at TexasStormChasers.com/live - Something with the imap/sn code is messed up so its not showing me on SN streaming, but I am.

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