SPC Aug 3, 2012 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0238 PM CDT FRI AUG 03 2012 VALID 032000Z - 041200Z ...THERE IS A SLGT RISK OF SVR TSTMS OVER THE NRN PLAINS... ...THERE IS A SLGT RISK OF SVR TSTMS OVER CNTRL MS AND AL... ...NRN PLAINS... NO CHANGES TO THE NRN PLAINS SLIGHT RISK. STORMS ARE BEGINNING TO INCREASE ACROSS CNTRL ND INTO N CNTRL SD...AND SHOULD CONTINUE TO EXPAND AND STRENGTHEN. ISOLATED VERY LARGE HAIL WILL REMAIN POSSIBLE WHILE STORMS ARE CELLULAR...WITH A DAMAGING WIND THREAT INCREASING LATER TODAY. FOR MORE INFORMATION SEE MESOSCALE DISCUSSION 1691. ...PA/MD/DE... EXPANDED LOW SEVERE PROBS ACROSS THE AREA WITH SEVERAL SMALL BUT INTENSE CORES NOTED ON RADAR. SPORADIC STRONG TO SEVERE STORMS MAY PERSIST FOR SEVERAL HOURS NEAR A DIFFUSE BOUNDARY AS HIGHER THETA-E AIR GRADUALLY SHIFTS NWD. ...MS/AL... A VERY MOIST AND UNSTABLE AIR MASS REMAINS OVER THE REGION WITH PWAT AROUND 2.25". A SMALL CLUSTER OF STORMS CURRENTLY EXISTS OVER W CNTRL AL...WHERE LOCALLY DAMAGING WINDS MAY OCCUR. OTHER STORMS WERE FORMING ACROSS SRN LA/MS/AL...AND MAY HAVE SOME PROPAGATION COMPONENT TO THE N. THUS...ADDITIONAL ACTIVITY CANNOT BE RULED OUT ACROSS CNTRL MS. ..JEWELL.. 08/03/2012 .PREV DISCUSSION... /ISSUED 1130 AM CDT FRI AUG 03 2012/ ...NRN PLAINS/MN AREA THROUGH TONIGHT... A WELL-DEFINED SHORTWAVE TROUGH IS MOVING ESEWD OVER CENTRAL/ERN MT THIS MORNING...WITH A PRONOUNCED BELT OF ASCENT PRECEDING THE TROUGH. AN ASSOCIATED COLD FRONT WILL PROGRESS EWD ACROSS THE DAKOTAS TO WRN MN OVERNIGHT...AND SEWD ACROSS THE NRN AND CENTRAL HIGH PLAINS BY 04/12Z. THIS FRONT WILL ACT AS THE PRIMARY FOCUS FOR THUNDERSTORM DEVELOPMENT LATER THIS AFTERNOON...AS SURFACE HEATING WEAKENS CONVECTIVE INHIBITION...AND THE BELT OF ASCENT BEGINS TO PHASE WITH THE SURFACE FRONT. REGIONAL 12Z SOUNDINGS REVEALED 7.5-9 C/KM MIDLEVEL LAPSE RATES OVER THE NRN PLAINS...WHERE SURFACE TEMPERATURES NEAR 90 F WILL LARGELY ELIMINATE THE CAP FROM BELOW...AND BOOST MLCAPE TO THE 2000-2500 J/KG RANGE. ELEVATED CONVECTION WILL LIKELY FORM SOONER ACROSS CENTRAL ND...WITH THE MORE CLEARLY SURFACE-BASED STORMS FORMING 19-21Z AS A RESULT OF HEATING/MIXING...IN COMBINATION WITH BOUNDARY LAYER DEWPOINTS IN THE 60S AND THE ARRIVAL OF THE MIDLEVEL ASCENT. STORMS WILL THEN SPREAD EWD/SEWD THROUGH THE EVENING/OVERNIGHT HOURS. MEANWHILE...DEEP-LAYER VERTICAL SHEAR WILL BECOME FAVORABLE FOR SUPERCELLS BY MID AFTERNOON WITHIN THE FIRST FEW HOURS AFTER INITIAL STORM DEVELOPMENT...WHEN THE LARGEST HAIL AND THE POSSIBILITY OF A TORNADO OR TWO IS EXPECTED. OTHERWISE...STORMS WILL TEND TO MERGE/GROW UPSCALE INTO CLUSTERS AND LINE SEGMENTS ALONG THE FRONT...WITH THE RISK FOR DAMAGING WINDS THROUGH EARLY TONIGHT. ...MS/AL THIS AFTERNOON... REMNANT OVERNIGHT CONVECTION PERSISTS AS OF MID MORNING OVER NRN MS...IN ADVANCE OF A WEAK MIDLEVEL TROUGH MOVING SEWD OVER TN. STRONG SURFACE HEATING AND RICH BOUNDARY LAYER MOISTURE TO THE S OF THE ONGOING STORMS WILL RESULT IN MLCAPE VALUES INCREASING TO 3000-4000 J/KG...AND CONVECTIVE INHIBITION WILL BE LARGELY REMOVED ONCE SURFACE TEMPERATURES REACH 90 F. STRONG INSTABILITY...THE ERN EXTENT OF THE STEEP LAPSE RATE PLUME FROM THE SRN PLAINS...AND 25-30 KT MIDLEVEL NWLY FLOW SAMPLED BY THE VWP/S AT NQA AND GWX...WILL SUPPORT ORGANIZED MULTICELL CLUSTERS WITH THE POTENTIAL TO PRODUCE DAMAGING WINDS AND ISOLATED LARGE HAIL. ...SE KS TO MO/SRN IL/WRN KY THIS AFTERNOON... AN MCV OVER ERN KS WILL CONTINUE TO MOVE GENERALLY EWD ACROSS MO THIS AFTERNOON...INVOF A DIFFUSE REMNANT FRONTAL SEGMENT. SURFACE HEATING IN THE WAKE OF MORNING CONVECTION AND IN ADVANCE OF THE MCV CLOUD SHIELD...ESPECIALLY ACROSS SE MO/SRN IL...COULD SUPPORT ADDITIONAL THUNDERSTORM DEVELOPMENT THIS AFTERNOON. CONFIDENCE IS SOMEWHAT LOW IN DETAILS OF HOW/WHEN ADDITIONAL STORMS WILL FORM...SO WILL OPT TO MAINTAIN LOW WIND/HAIL PROBABILITIES. ...INTERIOR NY/NEW ENGLAND THIS AFTERNOON... A SURFACE COLD FRONT WILL CROSS THE SAINT LAWRENCE VALLEY AND MOVE INTO NRN NY/NEW ENGLAND THIS AFTERNOON...WITH MODEST MOISTURE/INSTABILITY EXPECTED S OF THE FRONT AS TEMPERATURES WARM INTO THE 80S. AN ASSOCIATED LOW-AMPLITUDE SHORTWAVE TROUGH AND BELT OF STRONGER FLOW WILL REMAIN N OF THE INTERNATIONAL BORDER...THUS VERTICAL SHEAR AND FORCING FOR ASCENT WILL REMAIN RATHER WEAK ACROSS NY/NEW ENGLAND. STILL...DAYTIME HEATING AND WEAK ASCENT ALONG THE FRONT...AS WELL AS LOCAL TERRAIN INFLUENCES...SHOULD SUPPORT ISOLATED-WIDELY SCATTERED THUNDERSTORM DEVELOPMENT THIS AFTERNOON. THE STRONGEST STORMS COULD PRODUCE STRONG DOWNBURST WINDS AND MAINLY SUB-SEVERE HAIL...PRIOR TO STABILIZATION OF THE BOUNDARY LAYER THIS EVENING. Read more

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