SPC 2000Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0300 PM CDT THU APR 26 2012 VALID 262000Z - 271200Z ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE CENTRAL AND SRN HIGH PLAINS... ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS KY/TN TO SC AND SRN NC... ...KY/TN... DESPITE WEAK LOW LEVEL CONVERGENCE ALONG A COLD FRONT MOVING SWD ACROSS KY AT THIS TIME...ASCENT ATTENDANT WITH THE APPROACH OF AN UPSTREAM SUBTLE MIDLEVEL TROUGH /NOW LOCATED OVER IL/IND/ IS EXPECTED TO SUPPORT DEEPER MOIST CONVECTION. THE SLIGHT RISK AND SEVERE PROBABILITIES HAVE BEEN EXPANDED WWD ACROSS WRN KY/TN TO ACCOUNT FOR THE CURRENT LOCATION OF THE COLD FRONT AND PRE-FRONTAL CORRIDOR OF MODERATE INSTABILITY WHICH EXTENDED FROM TN INTO MUCH OF KY. FOR ADDITIONAL DETAILS...REFER TO ATTENDANT MESOSCALE DISCUSSIONS AND WW 191. ...NRN SC/SRN NC TO ERN NC/SERN VA... THE SLIGHT RISK AREA HAS BEEN EXTENDED ENEWD ALONG THE SC/NC BORDER ATTENDANT TO AN ONGOING ZONE OF STRONG TO SEVERE STORMS IN THIS REGION...PER REGIONAL RADAR IMAGERY...AND CORRESPONDING TO THE ESEWD EXTENT OF MODERATE INSTABILITY. THIS COMBINED WITH STRONG EFFECTIVE BULK SHEAR OVER NC/NRN SC AND ERN EXTENT OF EML /MIDLEVEL LAPSE RATES AROUND 7.5 C PER KM/ FAVORS THE POTENTIAL FOR ORGANIZED STORMS/SUPERCELLS INTO THE EARLY EVENING. FARTHER ENE...A MIDLEVEL CIRCULATION ATTENDANT TO THE EARLIER MCS WILL MOVE EWD ACROSS SERN VA/NERN NC AND SHOULD MOVE OFFSHORE BY EARLY EVENING. VEERED LOW LEVEL WINDS LIMITING LOW LEVEL CONVERGENCE ACROSS THIS REGION COMBINED WITH WEAK INSTABILITY SHOULD MAINTAIN A MARGINAL ENVIRONMENT FOR STRONG STORM DEVELOPMENT. THUS...THIS OUTLOOK HAS REDUCED THE SEVERE PROBABILITIES TO 5 PERCENT THREAT FOR ISOLATED HAIL AND/OR STRONG WIND GUSTS. ...SRN HIGH PLAINS... THE SLIGHT RISK/SEVERE PROBABILITIES HAVE BEEN EXPANDED SWD TO INCLUDE MORE OF W TX AND E CENTRAL NM...GIVEN THE DEVELOPMENT OF CU WITH SWD EXTENT PER VISIBLE SATELLITE IMAGERY...AND THE PRESENCE OF STRONGER INSTABILITY OVER THE SRN TX PANHANDLE REGION. FOR ADDITIONAL SHORT TERM DETAILS...REFER TO MESOSCALE DISCUSSION 592. OTHERWISE...THE REST OF THE HIGH PLAINS SLIGHT RISK FORECAST REMAINS ON TRACK. ...PARTS OF WRN AND CENTRAL MT... OBJECTIVE ANALYSES INDICATED AN AREA OF MARGINAL INSTABILITY WITH MUCAPE OF 500-1000 J/KG ACROSS CENTRAL INTO PART OF WRN MT. REGIONAL RADARS AND LIGHTNING DATA INDICATED A NNW-SSE ORIENTED BAND OF TSTMS OVER CENTRAL/SRN ID. THIS ACTIVITY APPEARS TO BE LOCATED ALONG THE LEADING EDGE OF STRONGER FORCING FOR ASCENT ATTENDANT TO A MIDLEVEL SHORTWAVE TROUGH LIFTING NEWD ACROSS THE NRN INTERMOUNTAIN REGION THIS PERIOD. STRENGTHENING SLY MIDLEVEL WINDS/SHEAR ACROSS THE DISCUSSION AREA SHOULD SUPPORT SOME STORM ORGANIZATION AS ADDITIONAL STORMS DEVELOP WITH THE APPROACH OF THE TROUGH. WEAK INSTABILITY WILL TEND TO LIMIT THE OVERALL COVERAGE OF STRONG TO SEVERE STORMS. THUS...THIS OUTLOOK WILL MAINTAIN LOW SEVERE PROBABILITIES FOR HAIL AND STRONG WIND GUSTS. ..PETERS.. 04/26/2012 .PREV DISCUSSION... /ISSUED 1130 AM CDT THU APR 26 2012/ ...SRN/CENTRAL HIGH PLAINS THIS AFTERNOON TROUGH TONIGHT... A COMPACT SHORTWAVE TROUGH OVER SRN CA THIS MORNING WILL EJECT ENEWD TO THE FOUR CORNERS THIS EVENING AND SE CO-NRN TX PANHANDLE BY 27/12Z...IN RESPONSE TO THE INLAND MOVEMENT OF A LARGER-SCALE TROUGH OVER THE PAC NW. LEE CYCLOGENESIS WILL OCCUR ACROSS THE HIGH PLAINS OF E/SE CO LATER TODAY INTO TONIGHT IN ADVANCE OF THE MIDLEVEL TROUGH. THE LEE CYCLOGENESIS WILL INDUCE STRENGTHENING SELY LOW-LEVEL FLOW AND NWWD ADVECTION OF THE 55-65 F BOUNDARY LAYER DEWPOINTS NOW OBSERVED ACROSS WRN OK/ERN TX PANHANDLE... BENEATH A VERY WARM ELEVATED MIXED LAYER. GIVEN THE PRESENCE OF THE STRONG CAP...RELATIVELY LATE ARRIVAL OF THE SHORTWAVE TROUGH... AND A SUBSTANTIAL PLUME OF MID/HIGH-LEVEL MOISTURE/CLOUDS...THE MORE PROBABLE AREA FOR DAYTIME STORM INITIATION WILL BE ON THE HIGH PLAINS FROM NE NM INTO SE CO. HERE...AFTERNOON TEMPERATURES OF 80-85 F WILL BE SUFFICIENT TO REMOVE CONVECTIVE INHIBITION...AND STORM DEVELOPMENT IS EXPECTED ALONG THE SHARPENING LEE TROUGH. THE INITIAL STORMS WILL LIKELY BE HIGH-BASED SUPERCELLS CAPABLE OF PRODUCING LARGE HAIL/DAMAGING WINDS GIVEN SOMEWHAT LIMITED BOUNDARY LAYER MOISTURE THIS AFTERNOON...WHILE THE LOWER PLAINS REMAIN CAPPED. TONIGHT...FOCUSED ASCENT IN ADVANCE OF THE MIDLEVEL TROUGH WILL HELP ERODE THE CAP...AS A WARM FRONT MOVES NWD ACROSS THE TX PANHANDLE/WRN OK AND RICHER MOISTURE SURGES NWWD. LOW-LEVEL SHEAR WILL LIKEWISE INCREASE...RESULTING IN AN ENVIRONMENT THAT IS MORE FAVORABLE FOR A COUPLE OF NOCTURNAL TORNADIC SUPERCELLS FROM EXTREME SE CO INTO SW KS. THE SRN EXTENT OF THE OVERNIGHT SEVERE THREAT BECOMES MORE QUESTIONABLE DUE TO STRONGER CAPPING. ...ERN NC/SE VA THIS AFTERNOON... A WELL-DEVELOPED MCS FROM EARLIER THIS MORNING WEAKENED ACROSS UPSTATE SC AND CENTRAL NC AS IT ENCOUNTERED AT BEST MARGINAL INSTABILITY. THOUGH BOUNDARY LAYER DEWPOINTS WILL REMAIN IN THE MID-UPPER 50S AHEAD OF THE MCS REMNANTS...SURFACE HEATING AND THE WELL-DEVELOPED NATURE OF THE MCV COULD PROMOTE SOME REJUVENATION OF CONVECTION THIS AFTERNOON ALONG THE LEADING EDGE OF THE COLD POOL. ISOLATED DAMAGING GUSTS WILL BE THE MAIN CONCERN. ...KY/TN AREA THIS AFTERNOON INTO EARLY TONIGHT... LOW-LEVEL AIR MASS RECOVERY IS UNDERWAY ACROSS KY/TN IN THE WAKE OF EARLY MORNING CONVECTION. THE REMNANT COLD POOL WILL CONTINUE TO ERODE FROM W-E AS SURFACE TEMPERATURES WARM WELL INTO THE 70S AND BOUNDARY LAYER DEWPOINTS IN THE LOW-MID 60S SPREAD ENEWD FROM THE MS VALLEY. ADDITIONAL THUNDERSTORM DEVELOPMENT IS EXPECTED THIS AFTERNOON ALONG A SURFACE COLD FRONT THAT IS MOVING SEWD ACROSS THE OH RIVER AS OF 16Z...AS AN UPSTREAM SPEED MAX APPROACHES FROM NRN IL. ...FOUR CORNERS THIS AFTERNOON... A PRONOUNCED BELT OF ASCENT PRECEDING THE EJECTING MIDLEVEL TROUGH IS ALREADY SUPPORTING A BAND OF CONVECTION NEAR THE RIM IN CENTRAL AZ. THIS CONVECTION WILL SPREAD ENEWD THROUGH THE AFTERNOON/EVENING...WITH AN ACCOMPANYING RISK FOR ISOLATED STRONG GUSTS.
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_2000.html
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