Oklahoma Weather Forecast: Storms Expected

Day 2 Convective Outlook NWS Storm Prediction Center Norman Ok 1228 Pm Cdt

Mon May 20 2013

VALID 211200Z - 221200Z

...THERE IS A MDT RISK OF SVR TSTMS OVER NERN TX...EXTREME SERN OK...CENTRAL AND SRN AR...AND NWRN LA...

...THERE IS A SLGT RISK OF SVR TSTMS FROM TX INTO THE GREAT LAKES REGION...

...SYNOPSIS... UPPER FLOW PATTERN IS FORECAST TO CHANGE SLOWLY THROUGH TOMORROW AS AN UPPER LOW OVER THE NRN PLAINS DRIFTS EWD AND WEAKENS GRADUALLY WHILE AN UPSTREAM COLD LOW DROPS SEWD ALONG THE PACIFIC NW COAST. A SHORT WAVE TROUGH EVIDENT NOW OVER THE FOUR-CORNERS AREA IS EXPECTED TO TRANSLATE EWD ACROSS THE SRN PLAINS DURING THE AFTERNOON BEFORE LIFTING NEWD AND BECOMING ABSORBED INTO THE SERN PERIPHERY OF THE NRN PLAINS UPPER LOW. IN THE SOUTHEAST...A WEAK UPPER LOW IS FORECAST TO DRIFT OVER THE FL PENINSULA.

AT THE SURFACE...A LOW OVER THE UPPER MIDWEST WILL EVOLVE SLOWLY EWD AND WEAKEN GRADUALLY...WHILE A TRAILING COLD FRONT EXTENDING SWWD FROM THE LOW ACROSS THE MIDDLE MS VALLEY SWWD INTO OK AND TX WILL DRIFT SEWD. CURRENT INDICATIONS ARE THAT PRE-FRONTAL CONVECTION DURING THE DAY 1 OVERNIGHT HOURS WILL RESULT IN OUTFLOW BOUNDARIES LOCATED WITHIN THE WARM SECTOR AT THE START OF THE PERIOD...AND THESE ARE EXPECTED TO PROVIDE AN ADDITIONAL FOCUS FOR SUBSEQUENT THUNDERSTORM REDEVELOPMENT DURING THE DIURNAL HEATING CYCLE ON TUESDAY.

...AR/SERN OK/NERN AND CENTRAL TX... MODEL CONSENSUS /INCLUDING CONVECTION-ALLOWING MODEL ENSEMBLES/ SUGGESTS THAT CONVECTION WILL BE OVER PARTS OF AR/OK AND NRN TX EARLY IN THE PERIOD...WITH A COMPOSITE OUTFLOW BOUNDARY EXTENDING FROM SERN AR INTO NERN/NORTH CENTRAL TX EARLY IN THE PERIOD. SOUTH OF THE BOUNDARY A WARM/MOIST AIR MASS WILL BE PRESENT WITH SURFACE DEW POINTS IN THE UPPER 60S-LOWER 70S...AND WITH ENHANCED DIABATIC HEATING ANTICIPATED INTO THE AFTERNOON COUPLED WITH PRE-EXISTING MODERATE MID-LEVEL LAPSE RATES...MLCAPE OF 3000-3500 J/KG IS EXPECTED BY THE AFTERNOON. AS THE AFOREMENTIONED SHORT WAVE TROUGH PROGRESSES EWD ACROSS THE SRN PLAINS DURING THE AFTERNOON...STORM INITIATION IS EXPECTED FROM SERN OK/SWRN AR INTO PARTS OF NRN TX NEAR THE EARLIER OUTFLOW BOUNDARY. ADDITIONAL STORMS ARE LIKELY TO DEVELOP SWWD NEAR/AHEAD OF THE WEAKENING FRONT INTO CENTRAL TX...WITH ALL ACTIVITY SPREADING EWD/NEWD THROUGH THE EVENING HOURS.

ALTHOUGH LOW-LEVEL WINDS WILL GENERALLY BE AOB 20-25 KT...FORECAST SOUNDINGS INDICATE WINDS WILL INCREASE AND VEER WITH HEIGHT IN RESPONSE TO THE PROGRESSIVE SHORT WAVE TROUGH...PROVIDING SUFFICIENT VERTICAL SHEAR FOR ORGANIZED CONVECTIVE STRUCTURES INCLUDING A FEW SUPERCELLS TO DEVELOP. VERY LARGE HAIL...DAMAGING WIND GUSTS...AND POSSIBLY A FEW TORNADOES WILL BE POSSIBLE...ESPECIALLY WHERE BOUNDARY INTERACTIONS MAY ENHANCE LOW LEVEL SHEAR/SRH. ACTIVITY IS EXPECTED TO GROW UPSCALE BY EVENING WITH SEVERAL QLCS/S FORMING WHICH MAY RESULT IN AN INCREASE IN WIND DAMAGE POTENTIAL. ACTIVITY IS THEN EXPECTED TO WEAKEN GRADUALLY BY 03-6Z AS THE SHORT WAVE TROUGH LIFTS NEWD AWAY FROM THE REGION AND DIURNAL COOLING BEGINS TO STABILIZE THE BOUNDARY LAYER.

...MID MS VALLEY NEWD INTO THE GREAT LAKES REGION... OVERNIGHT CONVECTION ACROSS MUCH OF THIS REGION WILL TEMPORARILY STABILIZE THE LOCAL ENVIRONMENT AT THE BEGINNING OF THE PERIOD...AND WILL RESULT IN A COMPLEX MESOSCALE SURFACE PATTERN WITHIN THE WARM SECTOR. AS CONVECTION CONTINUES TO WEAKEN OVER THIS AREA DURING THE MORNING...BREAKS IN CLOUDS WILL PERMIT REGIONS OF ENHANCED DIABATIC HEATING AND DESTABILIZATION TO OCCUR AMIDST A WARM/MOIST LOW LEVEL ENVIRONMENT. ZONES OF ENHANCED LOW LEVEL CONVERGENCE ALONG REMNANT OUTFLOW BOUNDARIES WILL PROVIDE A FOCUS FOR STORM REDEVELOPMENT BY EARLY-MID AFTERNOON. SWLY MID LEVEL WINDS OF 35-45 KT WILL PROVIDE SUFFICIENT DEEP LAYER SHEAR FOR ORGANIZED STRONG/SEVERE STORMS TO DEVELOP...WITH A THREAT FOR LARGE HAIL...DAMAGING WINDS...AND POSSIBLY A FEW TORNADOES MAINLY THROUGH THE EVENING HOURS.

THERE IS ALSO POTENTIAL FOR SEPARATE BANDS OF STRONG/SEVERE THUNDERSTORMS TO DEVELOP ALONG/AHEAD OF THE COLD FRONT ARCING ACROSS WI DURING THE AFTERNOON AND EVENING.

...LOWER GREAT LAKES INTO NY/WRN MA... GUIDANCE INDICATES STRONGER STORMS WILL BE POSSIBLE ALONG/NORTH OF A WARM FRONT LIFTING SLOWLY NWD ACROSS THIS AREA. ALTHOUGH LOW LEVEL MOISTURE WILL BE INCREASING...WEAKER MID LEVEL LAPSE RATES WILL TEND TO LIMIT THE OVERALL MAGNITUDE OF INSTABILITY WITH MLCAPE OF 1000-1500 J/KG EXPECTED. THERE WILL BE POTENTIAL FOR ISOLATED SEVERE STORMS DURING THE AFTERNOON AND EVENING...BUT WITH THE STRONGER MID LEVEL WINDS EXPECTED TO BE DISPLACED NWD AWAY FROM THE WARM FRONT...POTENTIAL FOR A MORE WIDESPREAD THREAT WILL BE LIMITED. IF LARGER INSTABILITY THAN CURRENTLY EXPECTED DEVELOPS...AN UPGRADE TO SLIGHT RISK MAY NEED TO BE CONSIDERED.

..WEISS.. 05/20/2013

ENDS

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