SPC 1730Z Day 2 Outlook
DAY 2 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1225 PM CDT SAT APR 13 2013 VALID 141200Z - 151200Z ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF SRN KS/NRN OK... ...SYNOPSIS... LARGE-SCALE UPPER TROUGHING IS FORECAST TO CONTINUE EXPANDING ACROSS THE WRN U.S. ON SUNDAY...AS A LOW SHIFTS ACROSS THE NRN PLAINS AND A SECOND BATCH OF ENERGY DIGS SSWWD ALONG THE WRN NOAM COAST INTO THE PAC NW. DOWNSTREAM OF THIS LARGE/DEVELOPING TROUGH...A WEAKER SRN STREAM TROUGH CROSSING THE S CENTRAL U.S. IS PROGGED TO SHIFT ACROSS THE GULF COAST STATES/SERN U.S. THROUGH THE PERIOD. WIDESPREAD PRECIPITATION DRIVEN BY STRONG QG FORCING AHEAD OF THIS SYSTEM SHOULD MAINTAIN A BAROCLINIC ZONE NEAR THE GULF COAST -- THUS LIMITING DESTABILIZATION/SEVERE POTENTIAL ACROSS MOST OF THE SERN CONUS. FARTHER W...A COLD FRONT WILL ADVANCE SEWD ACROSS THE CENTRAL U.S. WITH TIME...AS THE AFOREMENTIONED NRN PLAINS UPPER LOW PROGRESSES ENEWD. THIS FRONT WILL FOCUS SHOWERS AND THUNDERSTORMS...AND LIMITED SEVERE POTENTIAL DURING THE AFTERNOON AND EARLY EVENING HOURS. ...PARTS OF SRN KS/NRN OK... WHILE SLY BOUNDARY LAYER FLOW IN RESPONSE TO HIGH PLAINS CYCLOGENESIS WILL ALLOW AN INCREASE IN LOW-LEVEL MOISTURE ACROSS THE SRN PLAINS...A CAPPING INVERSION IS FORECAST TO PERSIST -- LIKELY RESULTING IN LOW-LEVEL CLOUD COVER IN MANY AREAS INTO THE AFTERNOON. AS A COLD FRONT PROGRESSES SEWD ACROSS IA/MO/KS AND INTO NRN OK...INCREASING ASCENT WILL AID IN WEAKENING OF THE CAP...AND EVENTUALLY CONVECTIVE DEVELOPMENT IS EXPECTED FROM SRN WI/IA SWWD TO ERN KS. DESPITE FAVORABLE SHEAR...VERY MODEST INSTABILITY ACROSS THIS PORTION OF THE AREA SUGGESTS ONLY A LOW-PROBABILITY THREAT FOR HAIL/WIND WITH THE STRONGEST CELLS. GREATER LOW-LEVEL MOISTURE/INSTABILITY WILL EXIST FARTHER S ACROSS SRN KS/OK -- BUT AGAIN...DEGREE OF CAPE WILL BE MODULATED BY POTENTIAL FOR LINGERING LOW CLOUD COVER AS MOISTURE STREAMS NWD BENEATH SUBSTANTIAL LOW-LEVEL CAPPING. IF CLOUDINESS ERODES SUFFICIENTLY TO PERMIT GRADUAL CAP WEAKENING/DESTABILIZATION -- FRONTAL ASCENT SHOULD THEN ALLOW AMPLE ADDITIONAL CAP EROSION FOR ISOLATED/LATE AFTERNOON STORM DEVELOPMENT. WITH 50 KT MID-LEVEL WLYS ATOP THE LOW-LEVEL SLY FLOW...SHEAR WILL BE SUFFICIENT FOR UPDRAFT ROTATION...AND ATTENDANT THREATS FOR DAMAGING WINDS AND HAIL -- AND POSSIBLY AN ISOLATED TORNADO. HOWEVER...WITH THE NUMBER OF STORMS INTO SRN KS/NRN OK LIKELY TO REMAIN LIMITED AND WITH EVENING COOLING LIKELY TO LIMIT THE THREAT TEMPORALLY...WILL MAINTAIN ONLY A SMALL 15%/SLIGHT RISK AREA ATTM. ...SRN GA/FL AND VICINITY... UNCERTAINTY PERSISTS ACROSS THE SERN U.S. THIS FORECAST AS POTENTIAL FOR/DEGREE OF INLAND PENETRATION OF HIGHER THETA-E AIR REMAINS DIFFICULT TO DISCERN. THE LATEST NAM RUN DEVELOPS A WEAK SURFACE LOW INVOF MOB DURING THE AFTERNOON...WHICH THEN SHIFTS NWD ACROSS AL TO WRN TN LATE IN THE PERIOD. UNDER THIS SCENARIO...WITH BOUNDARY LAYER FLOW TURNING SLY ACROSS ERN AL/GA/FL...SURFACE-BASED CONVECTION -- AND ISOLATED TORNADO POTENTIAL -- WOULD SPREAD NWD ACROSS AT LEAST SERN AL/SRN GA AND THE FL PANHANDLE THROUGH THE EVENING/OVERNIGHT. HOWEVER...THE GFS DOES NOT DEPICT THIS CYCLOGENESIS...WITH THE SURFACE WARM FRONT REMAINING NEAR OR S OF THE FL PANHANDLE AND EVENTUAL CYCLOGENESIS TO OCCUR LATE IN PERIOD OFF THE GA/SC COAST. ATTM...IT APPEARS THAT A GFS-TYPE SCENARIO IS MORE PROBABLE...AS WIDESPREAD ONSHORE/ELEVATED CONVECTION IS EXPECTED TO BE ONGOING EARLY ACROSS THE GULF COAST REGION IN RESPONSE TO STRONG LOW-LEVEL WARM ADVECTION. WITH THIS PRECIPITATION EXPECTED TO CONTINUE/ADVANCE EWD WITH TIME ACROSS THE NRN GULF AND GULF COAST STATES...SWD SUPPRESSION OF THE WARM FRONT SEEMS CONSISTENT. THUS -- WHILE NUDGING 5% SEVERE PROBABILITY NWD ACROSS SRN GA TO REFLECT LOW-PROBABILITY POTENTIAL FOR FARTHER NWD ADVANCE OF THE HIGH THETA-E GULF BOUNDARY LAYER -- IT APPEARS ATTM THAT LITTLE SEVERE THREAT WILL EXIST AWAY FROM THE COAST. FARTHER E ACROSS THE FL PENINSULA...GREATER AFTERNOON HEATING/DESTABILIZATION WILL OCCUR...BUT LARGE-SCALE ASCENT APPEARS LIKELY TO REMAIN W OF THE REGION UNTIL AFTER SUNSET. THUS...DEGREE OF AFTERNOON CONVECTIVE COVERAGE SHOULD REMAIN SOMEWHAT LIMITED -- LIKELY TIED TO SEA-BREEZE CIRCULATIONS. WITH DEEP-LAYER SHEAR SUPPORTIVE OF ORGANIZED STORMS...LOW-PROBABILITY SEVERE THREAT REMAINS JUSTIFIED FOR ISOLATED AFTERNOON STORMS...BUT WILL REFRAIN FROM ANY PROBABILITY UPGRADE ATTM UNTIL DEGREE OF AFTERNOON CONVECTIVE COVERAGE BECOMES MORE CERTAIN. ..GOSS.. 04/13/2013
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day2otlk_1730.html
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