SPC 1300Z Day 1 Outlook
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
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_1300.html
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