SPC 1200Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1255 AM CDT SAT APR 28 2012 VALID 281200Z - 291200Z ...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS SRN PLAINS... ...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS ERN MO TO OH VALLEY REGION... ...SYNOPSIS... KEY UPPER-AIR FEATURE FOR THIS FCST WILL BE STG SHORTWAVE TROUGH AND EMBEDDED CYCLONE NOW OVER MT/WY. 500-MB CYCLONE CENTER SHOULD BE LOCATED INVOF BLACK HILLS AT 28/12Z...WITH CONSENSUS AMONG VARIOUS OPERATIONAL/SREF PROGS FOR GEN NWD DRIFT OVER WRN DAKOTAS THROUGH PERIOD. BROADLY CYCLONIC FLOW WILL COVER MUCH OF ROCKIES AND GREAT PLAINS STATES AROUND THIS SYSTEM. PRECEDING/LOWER-AMPLITUDE PERTURBATION -- NOW EVIDENT IN MOISTURE CHANNEL IMAGERY AND VWP/PROFILER DATA OVER NEB/IA BORDER REGION -- WILL WEAKEN FURTHER AND MOVE THROUGH IA MEAN RIDGE POSITION EARLY IN PERIOD. SEGMENT OF ASSOCIATED VORTICITY BANNER WILL BREAK EWD ACROSS WI/SRN LM/LOWER MI REGION DURING AFTERNOON/EVENING. AT SFC...CYCLONE NOW OVER NERN KS/SERN NEB REGION IS FCST TO MOVE EWD ACROSS NRN MO EARLY IN PERIOD AND WEAKEN...WITH REMNANT FRONTAL WAVE STILL POSSIBLE OVER PORTIONS SRN IL OR ERN MO THIS AFTERNOON. BY 29/00Z...QUASISTATIONARY FRONT SHOULD EXTEND FROM THAT WAVE EWD ACROSS OH VALLEY TO NERN KY. COLD FRONT NOW SW OF THAT LOW WILL SETTLE SEWD ACROSS WRN/NRN OK EARLY IN PERIOD...THEN BY 29/00Z...BECOME QUASISTATIONARY FROM S-CENTRAL MO TO SWRN OK AND NW TX...THEN WWD ACROSS TX SOUTH-PLAINS REGION. DRYLINE SHOULD EXTEND FROM FRONTAL INTERSECTION OVER NW TX...SSWWD TO NRN COAHUILA/BIG BEND AREA. ...SRN PLAINS... SVR POTENTIAL ACROSS THIS REGION APPEARS IN TWO PRIMARY MODES...EACH WITH SOME CONDITIONALITIES INVOLVED... 1. NEAR-SFC FRONTAL ZONE...CENTRAL OK TO W-CENTRAL TX...LATE AFTERNOON INTO EVENING. IT NOW APPEARS THAT AT LEAST ISOLATED TO WIDELY SCATTERED TSTMS WILL FORM ALONG FRONTAL ZONE DURING LATE AFTERNOON INTO EARLY EVENING...TAKING ADVANTAGE OF LIFT ALONG BOUNDARY...SFC DEW POINTS UPPER 50S TO MID 60S F...MLCAPE NEAR 3000 J/KG IN SOME AREAS...AND 45-50 KT EFFECTIVE SHEAR. SUPERCELLS WITH DAMAGING HAIL AND STG-SVR GUSTS ARE POSSIBLE...THOUGH STORM MERGERS AND OUTFLOW MAY MAKE MODES MESSY LOCALLY. TORNADO THREAT WILL DEPEND STRONGLY ON STATUS OF CONVECTIVE MODE BY ABOUT 00Z-01Z...WHEN LOW-LEVEL HODOGRAPHS ARE FCST TO ENLARGE AND BECOME FAVORABLE. ANY DISCRETE SUPERCELLS STILL PRESENT AT THIS TIME MAY ENCOUNTER RELATIVELY BACKED FLOW ALONG SFC FRONT AND STRENGTHENING LLJ WINDS ABOVE THAT RESULT IN ENHANCED EFFECTIVE SRH. OTHERWISE...BAND OF FRONTAL TSTMS SHOULD AGGREGATE DURING EVENING...THEN DIMINISH IN INTENSITY BY ABOUT 06Z AS MLCINH BECOMES PROGRESSIVELY LESS FAVORABLE. 2. ELEVATED HAIL RISK FROM TX PANHANDLE AND PERHAPS EXTREME NERN NM ACROSS NWRN OK AND SRN KS OVERNIGHT. MODELS DIFFER ON MESOSCALE DETAILS OF TIMING/LOCATION. HOWEVER...CONSENSUS FAVORS FORMATION OF STG/ISOLATED SVR TSTMS WITH HAIL POSSIBLE DURING 29/06Z-29/12Z TIME FRAME BETWEEN TX PANHANDLE/NM BORDER REGION AND NRN OK/SRN KS. INCREASING MOISTURE...STEEP MIDLEVEL LAPSE RATES...AND ISENTROPIC ASCENT TO LFC SHOULD SUPPORT THIS RISK...WITH CORRIDOR OF 1000-2000 J/KG ELEVATED MUCAPE. 55-65 KT EFFECTIVE SHEAR IS FCST...LENDING SOME CONCERN FOR SIGNIFICANT HAIL OR GREATER COVERAGE THAN OUTLOOK INDICATES OVER SOME PORTION OF THIS AREA. HOWEVER...SPATIAL/TIMING UNCERTAINTIES PRECLUDE MORE THAN 5% UNCONDITIONAL FCST ATTM. ...ERN MO TO OH VALLEY REGION... SCATTERED TSTMS ARE EXPECTED TO DEVELOP INVOF SFC FRONT THIS AFTERNOON...WITH DAMAGING WIND AND OCNL LARGE HAIL POSSIBLE. PRIMARY MODE SHOULD BE MULTICELLULAR...THOUGH TRANSIENT SUPERCELL EVOLUTIONS CANNOT BE RULED OUT...GIVEN PRESENCE OF AT LEAST MRGL DEEP-LAYER SPEED SHEAR. SVR THREAT SHOULD BE STRONGLY TIED TO COMBINATION OF DIURNAL CAPE MAX ALONG AND S OF FRONT...AS WELL AS RELATIVELY MAXIMIZED ASCENT ALONG BOUNDARY NEAR AND E OF FRONTAL WAVE. ANTECEDENT MOIST ADVECTION SHOULD BOOST SFC DEW POINTS INTO MID-50S/MID-60S F RANGE OVER THIS CORRIDOR...JUXTAPOSED WITH LAPSE RATES THAT INCREASE GRADUALLY FROM E-W. RESULT SHOULD BE PRECONVECTIVE MLCAPE IN 1500-2500 J/KG RANGE...AMIDST 35-45 KT EFFECTIVE SHEAR MAGNITUDE. TSTMS SHOULD DIMINISH MARKEDLY AFTER DARK...WITH STABILIZATION RESULTING FROM COMBINATION OF SFC DIABATIC COOLING AND OUTFLOW POOLS. ..EDWARDS/GARNER.. 04/28/2012
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_1200.html
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