SPC 1300Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0747 AM CDT SAT MAY 26 2012 VALID 261300Z - 271200Z ...THERE IS A SLGT RISK OF SVR TSTMS FROM PORTIONS OF THE NRN PLAINS AND UPPER MIDWEST INTO SRN HIGH PLAINS... ...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON AND EVENING ACROSS PARTS OF ERN WY... ...SYNOPSIS... 80-90 KT MIDLEVEL JET STREAK OVER THE SWRN DESERTS WILL DEVELOP NEWD INTO THE NRN HIGH PLAINS BY 27/12Z IN TANDEM WITH A POTENT VORTICITY MAXIMUM. THE PROGRESSION OF THESE FEATURES WILL RESULT IN THE NET EWD/NEWD MOVEMENT OF WRN U.S. TROUGH THIS PERIOD...AND THE GRADUAL SUPPRESSION OF MIDLEVEL RIDGE ACROSS THE NRN/CNTRL PLAINS. DOWNSTREAM FROM THE LARGE-SCALE TROUGH...A SERIES OF WEAK VORTICITY MAXIMA FROM CNTRL KS INTO SWRN TX WILL TRANSLATE NNEWD WHILE SUBTROPICAL STORM BERYL ADVANCES SWWD TOWARD THE SERN ATLANTIC COAST. AT THE SURFACE...LEE CYCLONE OVER ERN CO WILL DEEPEN TODAY WHILE DEVELOPING SLOWLY NWD THROUGH THE CNTRL HIGH PLAINS. THIS FEATURE WILL BEGIN TO ACCELERATE NNEWD TONIGHT INTO CNTRL SD IN RESPONSE TO ABOVE-MENTIONED JET STREAK AND ASSOCIATED VORTICITY MAXIMUM. EXPECT A WARM FRONT TO CONCURRENTLY MOVE/DEVELOP NWD THROUGH THE MID-MO VALLEY INTO THE UPPER MS VALLEY/UPPER MIDWEST. THE ERN EXTENSION OF THIS BOUNDARY WILL ASSUME COLD FRONTAL PROPERTIES AS IT SETTLES SWD THROUGH CNTRL/SRN NEW ENGLAND AND THE NRN MID-ATLANTIC STATES. ELSEWHERE...A DRYLINE WILL STRENGTH TODAY ACROSS THE CNTRL/SRN HIGH PLAINS...PERHAPS MIXING EWD EARLY BEFORE RETREATING BY LATE AFTERNOON INTO THIS EVENING. ...NRN PLAINS INTO UPPER MIDWEST AND SWD INTO SRN HIGH PLAINS... A COUPLE OF ELEVATED TSTM COMPLEXES ARE ONGOING THIS MORNING...ONE OVER SERN SD /SWRN MN...AND THE OTHER ACROSS SRN WI/NRN IL. THIS ACTIVITY IS SITUATED WELL TO THE N OF SURFACE WARM FRONT AND LIKELY FORCED BY WAA AT THE TERMINUS OF A BIFURCATED LLJ. MASS RESPONSE TO WRN U.S. UPPER TROUGH WILL RESULT IN THE NWD MIGRATION OF THE WRN LLJ BRANCH INTO THE NRN PLAINS AND UPPER MIDWEST...LIKELY MAINTAINING EPISODIC ELEVATED TSTM DEVELOPMENT ALONG THE NRN EDGE OF THE STRONGER CAP/EML BEING ADVECTED NWD THROUGH THE CNTRL PLAINS/MID MS VALLEY REGION. GIVEN THE PRESENCE OF STEEP MIDLEVEL LAPSE RATES...A MOIST LOW-LEVEL ENVIRONMENT...AND RELATIVELY STRONG CLOUD BEARING SHEAR...THE MOST INTENSE STORMS WILL REMAIN CAPABLE OF LARGE HAIL AND PERHAPS LOCALLY DAMAGING WIND GUSTS. TO THE S OF THE ELEVATED TSTM REGIME...THE PRESENCE OF A STRONG CAP /REF. 12Z LBF AND OAX SOUNDINGS/ AND NEUTRAL TO ONLY SLIGHT MIDLEVEL HEIGHT FALLS THROUGH THE PEAK OF THE DIURNAL HEATING CYCLE CAST CONSIDERABLE UNCERTAINTY ON SURFACE-BASED STORM DEVELOPMENT LATER TODAY. CURRENT THINKING IS THAT THE HIGHEST PROBABILITY FOR STORM INITIATION WILL BE ALONG THE DRYLINE FROM CNTRL NEB SWWD INTO WRN TX WHERE THE DEVELOPMENT OF A HOT...DEEPLY-MIXED BOUNDARY LAYER MAY ALLOW FOR THE LOCAL EROSION OF THE CAP. A DYNAMICAL CONTRIBUTION TO STORM INITIATION MAY ALSO BE PROVIDED BY A COUPLE OF WEAK IMPULSES EMBEDDED IN SUBTROPICAL MOIST PLUME FROM KS INTO TX...THOUGH DETAILS REMAIN UNCLEAR. WHILE ENVIRONMENTAL CONDITIONS WILL SUPPORT SUPERCELLS CAPABLE OF LARGE HAIL AND DAMAGING WIND GUSTS ALONG THE LENGTH OF THE DRYLINE...THE OVERLAP OF STRONGEST INSTABILITY /MLCAPE OF 2000-4000 J PER KG/ AND VERTICAL SHEAR --AND POTENTIALLY GREATER SEVERE WEATHER THREAT-- WILL EXIST OVER THE NEB SANDHILLS INTO MID-MO VALLEY INVOF WARM FRONT/DRYLINE INTERSECTION. BUT...GIVEN UNCERTAINTIES IN STORM INITIATION...BASELINE SLIGHT RISK PROBABILITIES WILL BE MAINTAINED. ...WY... DEEP-LAYER FORCING FOR ASCENT WILL STRENGTHEN LATER TODAY INTO TONIGHT AS EXIT REGION OF ABOVE-MENTIONED MIDLEVEL JET STREAK GRADUALLY OVERSPREADS THE REGION. THIS WILL SUPPORT THE DEEPENING SUBSEQUENT NWD DEVELOPMENT OF LEE CYCLONE AND ATTENDANT WARM FRONT. LATEST MODEL GUIDANCE REMAINS CONSISTENT IN SUGGESTING THAT A NARROW AXIS OF MODEST INSTABILITY /I.E. MLCAPE OF 500-1000 J PER KG/ WILL DEVELOP INVOF SURFACE FRONT THIS AFTERNOON/EVENING...SUFFICIENT FOR ISOLATED-WIDELY SCATTERED TSTM DEVELOPMENT. GIVEN VERTICAL WIND PROFILES EXHIBITING PRONOUNCED VEERING WITH HEIGHT AND STRONG DEEP-LAYER SHEAR...SETUP MAY YIELD A FEW SUPERCELLS CAPABLE OF HAIL AND PERHAPS A TORNADO. ..MEAD/ROGERS.. 05/26/2012
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_1300.html
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