DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 281250
SWODY1
SPC AC 281249

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0749 AM CDT SAT APR 28 2012

VALID 281300Z - 291200Z

...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS OF THE SRN PLAINS...

...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS OF ERN MO / OH VALLEY
REGION...

UPPER FLOW REGIME ACROSS THE CONUS WILL FEATURE A SLOW MOVING CLOSED
MID-UPPER LOW NEAR THE BLACK HILLS WITH SEVERAL LOWER AMPLITUDE
PERTURBATIONS ROTATING THROUGH THE BASAL PORTION OF THE UPPER
TROUGH. A LEAD SHORTWAVE TROUGH WILL WEAKEN CONSIDERABLY AS IT
CONTINUES TOWARDS THE WRN GREAT LAKES AS ELEVATED MORNING TSTMS
DISSIPATE LATER THIS MORNING AS LOW LEVEL WAA CONCURRENTLY WEAKENS.
IN WAKE OF THIS DISTURBANCE...ANOTHER MID LEVEL WAVE IS EVIDENT
MOVING INTO NRN OK/SRN KS THIS MORNING...AND IS FORECAST TO APPROACH
THE LOWER OH RIVER VALLEY BY PEAK HEATING. ANOTHER UPSTREAM
DISTURBANCE OVER THE SRN GREAT BASIN WILL MOVE INTO THE SRN HIGH
PLAINS BY THIS EVENING. THESE SMALLER SCALE FEATURES WILL SERVE AS
FOCUS MECHANISMS FOR STRONG-SEVERE TSTMS DURING PEAK HEATING FROM
THE MID MS RIVER VALLEY INTO THE LOWER OH RIVER VALLEY...AND LATER
TODAY OVER A SEPARATE AREA ACROSS THE SRN PLAINS WITH THE SEVERE
RISK LINGERING INTO THE OVERNIGHT HOURS.

...SRN PLAINS...
SURFACE FRONT CURRENTLY DRAPED ACROSS PARTS OF W TX EXTENDING NEWD
NEAR THE I-44 CORRIDOR IN OK IS FORECAST TO MOVE LITTLE DURING THE
DAY. NEAR AND S OF THIS BOUNDARY...STRONG BOUNDARY LAYER HEATING
--TEMPS RISING INTO THE 80S-- WITHIN A SLY LOW LEVEL FETCH OF
LOWER-MID 60S DEWPOINTS WILL YIELD 2000-3000 J/KG MLCAPE. MODEL
FORECAST SOUNDINGS SHOW THE CAP WEAKENING CONSIDERABLY TOWARDS 00Z.
SUITE OF CONVECTION-ALLOWING MODELS HOWEVER TEND TO LIMIT TSTM
COVERAGE TO ISOLD CHANCES UNTIL THE MID-EVENING HOURS AS A CNTRL TX
LLJ INTENSIFIES /40 KTS/ AND ISENTROPIC LIFT INCREASES. DESPITE
COVERAGE/CAPPING CONCERNS...A BELT OF 35-50 KT H5 FLOW OVERTOP THE
REGION WILL BE FAVORABLE FOR ISOLD SUPERCELL DEVELOPMENT...ESP. NEAR
THE DRYLINE/FRONT INTERSECTION OVER WRN N-CNTRL TX/SWRN OK. A LARGE
TO VERY LARGE HAIL THREAT WILL BE POSSIBLE FOR ANY SURFACE-BASED
DAYTIME SUPERCELLS THAT DEVELOP. BACKED LOW LEVEL FLOW INVOF THE
FRONT WITH SOME INCREASE IN LOW LEVEL SHEAR TOWARDS DUSK MAY LEND AN
ISOLD TORNADO RISK WHERE SURFACE T/TD SPREADS LOWER BEFORE MLCINH
INCREASES...ACTING TO TEMPER THE TORNADO POTENTIAL. DURING THE
OVERNIGHT...TSTM COVERAGE IS FORECAST TO INCREASE /GENERALLY N OF
THE RED RIVER/ WITH MAINLY A LARGE HAIL/ISOLD DMGG WIND RISK
LINGERING INTO THE OVERNIGHT HOURS.

...ERN MO / OH VALLEY REGION...
A WARM FRONT OVER ERN MO INTO THE TN VALLEY WILL LIFT NWD INTO THE
OH VALLEY AS A SURFACE LOW WEAKENS EARLY IN THE PERIOD. AN INFLUX
OF RICHER MOISTURE CHARACTERIZED BY PBL DEWPOINTS RISING INTO THE
56-62 DEG F RANGE...SHOULD RESULT IN MODERATELY UNSTABLE AIRMASS BY
EARLY-MID AFTERNOON /1000-2000 J/KG MLCAPE/ WITH DECREASING CAPE
WITH EWD EXTENT. STRONG...ALBEIT LARGELY UNIDIRECTIONAL...WLY FLOW
WILL SUPPORT ORGANIZED SCTD STRONG-SEVERE STORM CLUSTERS DEVELOPING
BY AFTERNOON IN THE FORM OF MULTICELLS/SUPERCELLS -- PERHAPS
INITIALLY NEAR THE MS RIVER AND DEVELOPING EWD INVOF THE FRONTAL
ZONE SPREADING EWD TOWARDS THE CNTRL APPALACHIANS. ISOLD DMGG WIND
GUSTS WITH OCCASIONAL BOUTS OF LARGE HAIL WILL BE THE PRIMARY
THREATS WITH THESE STORMS...OWING TO A LACK OF APPRECIABLY STRONG
LOW LEVEL SHEAR...THEREBY LIMITING THE TORNADO RISK. THE ACTIVITY
SHOULD WEAKEN BY EVENING AS NOCTURNAL STABILIZATION/CONVECTIVE
OVERTURNING LIMIT THE DEGREE OF INSTABILITY.

..SMITH/HART.. 04/28/2012

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