SPC AC 121257
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0757 AM CDT WED MAY 12 2010
VALID 121300Z - 131200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON INTO TONIGHT
FROM THE SRN PLAINS TO THE MID MS AND OH VALLEYS...
...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTERNOON/EVENING FOR
THE MID ATLANTIC REGION...
...SYNOPSIS...
A CLOSED LOW OVER WRN CO WILL MOVE NNEWD TOWARD THE DAKOTAS BY
THURSDAY MORNING...WHILE THE ASSOCIATED MIDLEVEL TROUGH OVER THE
ROCKIES MAKES SLOW EWD PROGRESS TOWARD THE PLAINS. DOWNSTREAM...A
PRONOUNCED RIDGE WILL PERSIST FROM THE SE STATES TO THE GREAT LAKES.
THE INITIAL LEE CYCLONE WILL MOVE SLOWLY SWD AND WEAKEN TODAY INVOF
THE WRN OK/TX BORDER. A SEPARATE WAVE WILL DEVELOP NEWD TOWARD NRN
MO/SRN IA ALONG THE PRE-EXISTING BAROCLINIC ZONE ACROSS KS/MO...AND
IN RESPONSE TO AN EMBEDDED SHORTWAVE TROUGH OVER AZ THAT WILL EJECT
NEWD TO THE CENTRAL PLAINS BY TONIGHT. THIS BAROCLINIC ZONE WILL
PROVIDE THE FOCUS FOR EXTENSIVE THUNDERSTORM DEVELOPMENT LATER THIS
AFTERNOON THROUGH TONIGHT FROM THE SRN PLAINS TO THE MID MS VALLEY.
...SRN PLAINS TO MID MS VALLEY THROUGH TONIGHT...
CLUSTERS OF ELEVATED CONVECTION ARE SPREADING EWD/NEWD OVER MO/IA IN
ASSOCIATION WITH LOW-LEVEL WAA...WHILE A LARGER MCS AND EMBEDDED MCV
HAS EVOLVED FROM THE MASS OF THUNDERSTORMS ALONG THE STALLED FRONT
OVERNIGHT ACROSS MO/IL. IN THE WAKE OF THIS CONVECTION...A WARM
FRONT WILL MOVE NWD ACROSS KS/MO IN RESPONSE TO THE WEAK WAVE
DEVELOPING NEWD ACROSS KS. THUNDERSTORM DEVELOPMENT ALONG THE
TRAILING COLD FRONT ACROSS KS/NW OK WILL LIKELY BE DELAYED UNTIL
MID-LATE AFTERNOON...WHEN CONVECTIVE INHIBITION IS MINIMIZED AND
LOW-LEVEL CONVERGENCE/ASCENT STRENGTHENS. STRONG INSTABILITY WILL
BE PRESENT IN THE WARM SECTOR /MLCAPE RANGING FROM 2000 J/KG ACROSS
CENTRAL/NRN MO TO 3500 J/KG IN OK/...AND DEEP-LAYER VERTICAL SHEAR
WILL REMAIN FAVORABLE FOR SUPERCELLS. HOWEVER...LOW-LEVEL SHEAR
WILL BE RATHER MODEST IN THE WARM SECTOR /EFFECTIVE SRH OF 100-200
M2 PER S2/...WITH THE STRONGEST SHEAR EXPECTED NEAR AND E OF THE
SURFACE WAVE ALONG THE WARM FRONT.
THERE WILL BE A WINDOW OF OPPORTUNITY OF A FEW HOURS FOR RELATIVELY
DISCRETE SUPERCELLS WITH ISOLATED TORNADOES AND VERY LARGE HAIL THIS
AFTERNOON/EVENING...FROM NW OK INTO CENTRAL/NE KS AND NRN MO. MORE
ISOLATED DISCRETE STORMS MAY ALSO FORM LATE THIS AFTERNOON ALONG THE
REMNANT DRYLINE ACROSS SW OK AND NW TX. LATER THIS
EVENING...UPSCALE GROWTH INTO CLUSTERS/LINES IS EXPECTED IN RESPONSE
TO A LINEAR FOCUS FOR CONVECTIVE INITIATION ALONG THE FRONT AND
LARGELY FRONT-PARALLEL DEEP-LAYER FLOW/SHEAR VECTORS. THUS...LARGE
HAIL AND DAMAGING WINDS WILL BECOME THE PRIMARY SEVERE THREATS
OVERNIGHT...ALONG WITH AN INCREASING THREAT FOR LOCALLY HEAVY
RAINFALL.
...OH VALLEY THIS MORNING TO THE MID ATLANTIC THIS EVENING...
AN MCV ASSOCIATED WITH OVERNIGHT CONVECTION WILL CONTINUE TO MOVE
EWD OVER THE OH VALLEY THROUGH EARLY AFTERNOON...AND SHOULD REACH
THE MID ATLANTIC REGION THIS EVENING. A MOIST/UNSTABLE FEED ON THE
NOSE OF A 50 KT SWLY LLJ HAS SUPPORTED THE CONVECTION
OVERNIGHT...AND IT APPEARS THAT INSTABILITY WILL BE SUFFICIENT TO
MAINTAIN THE MCS INTO SRN OH/NRN KY THROUGH MIDDAY. ISOLATED LARGE
HAIL AND DAMAGING WINDS WILL BE POSSIBLE IN AN ENVIRONMENT OF
LARGELY UNIDIRECTIONAL WLY WIND PROFILES IN COMBINATION WITH
MODERATE INSTABILITY.
INSTABILITY WILL BE SOMEWHAT WEAKER FROM THE CENTRAL APPALACHIANS
EWD TO THE MID ATLANTIC COAST...AND SOME WEAKENING OF THE MCS IS
LIKELY THIS AFTERNOON ACROSS THE APPALACHIANS. THEREAFTER...IT IS
UNCLEAR WHETHER OR NOT THE CONVECTION WILL REGENERATE E OF THE
MOUNTAINS ACROSS VA/MD...THOUGH INSTABILITY AND DEEP-LAYER VERTICAL
SHEAR COULD STILL BE SUFFICIENT FOR A DAMAGING WIND AND MARGINALLY
SEVERE HAIL THREAT INTO THIS EVENING.
..THOMPSON/HURLBUT.. 05/12/2010
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
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