SPC 2000Z Day 1 Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0245 PM CDT TUE MAY 29 2012 VALID 292000Z - 301200Z ...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF NERN PA...PORTIONS OF UPSTATE NY...SRN VT AND NWRN MA... ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK AREA FROM NRN VA INTO EXTREME NWRN ME... ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE CNTRL/SRN PLAINS... ...THERE IS A SLGT RISK OF SVR TSTMS OVER THE COASTAL SERN U.S. IN RESPONSE TO BERYL... MINOR MODIFICATIONS HAVE BEEN MADE TO THE CURRENT SEVERE RISK ACROSS THE NERN U.S...NAMELY TO EXTEND THE MDT RISK INTO SRN NH AND EXTREME NWRN PARTS OF MA. NUMEROUS SEVERE THUNDERSTORMS HAVE DEVELOPED ALONG A CORRIDOR FROM CNTRL PA...NEWD INTO NH AND AMPLE SHEAR/INSTABILITY EXIST WITH/AHEAD OF THIS ACTIVITY TO WARRANT THIS EWD EXPANSION. A WELL DEFINED MARINE-INFLUENCED BOUNDARY IS STALLED ACROSS WRN NEW ENGLAND AND THIS WILL BE THE DEMARCATION OF MORE INTENSE UPDRAFTS/DOWNDRAFTS. WHILE SEVERE THUNDERSTORMS SHOULD SPREAD ATOP THIS COOLER BOUNDARY LAYER IT APPEARS THIS ACTIVITY SHOULD BECOME MORE ELEVATED IN NATURE AND HAIL THE PREDOMINANT THREAT. FARTHER WEST ACROSS THE CNTRL/SRN PLAINS...STRONG BOUNDARY LAYER HEATING IS CONTRIBUTING TO EXTREME INSTABILITY ACROSS OK WHERE MLCAPE VALUES ARE NOW ON THE ORDER OF 3000-4000 J/KG. WITH TEMPERATURES RISING INTO THE LOWER 90S IT APPEARS CONVECTIVE TEMPERATURES WILL SOON BE BREACHED AND TSTMS SHOULD EVOLVE BY 22Z. LATEST VIS IMAGERY SUPPORTS THIS WITH CU FIELD EXPANDING ACROSS WOODWARD/DEWEY/BLAINE COUNTIES. IN ALL LIKELIHOOD DEEP CONVECTION SHOULD EVOLVE FROM THIS DEEPENING CU AND ALONG THE FRONT ACROSS SWRN KS. 1630Z REASONING REMAINS VALID. ..DARROW.. 05/29/2012 .PREV DISCUSSION... /ISSUED 1142 AM CDT TUE MAY 29 2012/ ...SYNOPSIS... AN UPPER-LEVEL LOW ALONG THE MN/ONTARIO BORDER WILL GRADUALLY EVOLVE INTO AN OPEN WAVE DURING THE D1 PERIOD AS IT PROGRESSES ENEWD INTO WRN QUEBEC. THIS SYSTEM WILL BE ATTENDED BY A BELT OF 50-60 KT MIDLEVEL FLOW AND 500-MB HEIGHT FALLS OF 60-120 M/12-HR WHICH WILL OVERSPREAD THE ST. LAWRENCE VALLEY...LOWER GREAT LAKES...AND NEW ENGLAND. ELSEWHERE...MIDLEVEL HEIGHTS WILL REBOUND SLIGHTLY ACROSS THE GREAT PLAINS IN THE WAKE OF THE GREAT LAKES SYSTEM...AND AHEAD OF AN UPSTREAM UPPER SHORT-WAVE TROUGH TRANSLATING SEWD FROM SRN BRITISH COLUMBIA THROUGH THE NRN ROCKIES. AT THE SURFACE...A COLD FRONT INITIALLY FROM LOW PRESSURE OVER WRN QUEBEC SWWD THROUGH SWRN ONTARIO INTO THE MID-MS VALLEY WILL ADVANCE EWD INTO NEW ENGLAND AND THE MID-ATLANTIC STATES BY 30/12Z. THE WRN EXTENSION OF THIS BOUNDARY WILL REMAIN QUASI-STATIONARY...STRETCHING FROM THE OZARKS WWD TO AN AREA OF LOW PRESSURE OVER WRN OK AT 30/00Z. A DRYLINE IS FORECAST TO EXTEND SWD FROM THE LOW PRESSURE INTO W-CNTRL TX AND WRN PARTS OF THE EDWARDS PLATEAU REGION AT THIS TIME. MEANWHILE...TROPICAL DEPRESSION BERYL WILL BEGIN TO ACCELERATE NEWD FROM S-CNTRL GA THROUGH THE LOWER SAVANNAH RIVER VALLEY. ...NEW ENGLAND INTO THE LOWER GREAT LAKES AND MID-ATLANTIC STATES... AN EXPANSIVE PRE-FRONTAL BAND OF TSTMS IS ONGOING ACROSS PORTIONS OF WRN NY INTO THE KY/TN VALLEYS...FORCED BY THE LEADING EDGE OF STRONGER HEIGHT FALLS ASSOCIATED WITH THE UPPER SYSTEM MOVING THROUGH THE GREAT LAKES. AREAS OF CLEARING ACROSS MUCH OF THE NORTHEAST HAVE LED TO AMPLE SURFACE-BASED DESTABILIZATION. LITTLE IF ANY CONVECTIVE INHIBITION REMAINS GIVEN THE VERY WEAK LOW LEVEL INVERSION NOTED ON THE 12Z BUF AND ALBANY SOUNDINGS. DEW POINTS IN THE 60S TO LOWER 70S F COUPLED WITH MIDLEVEL LAPSE RATES AROUND 7 C/KM WILL CONTRIBUTE TO A MODERATELY-STRONGLY UNSTABLE AIR MASS WITH MLCAPE VALUES INCREASING TO 2000-3000 J/KG. THIS DESTABILIZATION ALONG WITH THE EWD PROGRESSION OF THE UPPER TROUGH WILL SUPPORT A MARKED INCREASE IN STORM VIGOR AND COVERAGE BY EARLY AFTERNOON ALONG THE COLD FRONT AND/OR LEADING EDGE OF THE COLD POOL ASSOCIATED WITH THE ONGOING STORMS. ADDITIONAL DEVELOPMENT IS POSSIBLE ALONG A REMNANT OUTFLOW BOUNDARY ACROSS THE MOHAWK VALLEY...AND A PRE-FRONTAL TROUGH OVER ERN NY/PA. ALTHOUGH THE STRONGEST MID- AND HIGH-LEVEL WIND FIELD ASSOCIATED WITH THE TROUGH IS FORECAST TO LAG THE WARM SECTOR TO THE W...LOW LEVEL WINDS WILL STRENGTHEN SOME ACROSS ERN NY AND WRN NEW ENGLAND. SHEAR PROFILES WILL BE SUFFICIENT FOR DMGG WINDS AND POTENTIALLY SUPERCELLS...ESPECIALLY INVOF THE HUDSON VALLEY. A TORNADO THREAT WILL ALSO EXIST ALONG THE WARM FRONT OVER PORTIONS OF NEW ENGLAND WHERE LOW-LEVEL SHEAR WILL BE ENHANCED. THE SEVERE WEATHER THREAT WILL SPREAD EWD TOWARD THE MID-ATLANTIC COAST AND WRN NEW ENGLAND BY LATE AFTERNOON INTO THIS EVENING BEFORE GRADUALLY DIMINISHING LATER TONIGHT WITH THE STABILIZATION OF THE BOUNDARY LAYER. ...CNTRL/SRN PLAINS... AS MENTIONED ABOVE...MIDLEVEL HEIGHTS WILL REBOUND SLIGHTLY TODAY WITH PASSAGE OF SYNOPTIC SYSTEM TO THE NE. AS SUCH...DAYTIME HEATING AND LOW-LEVEL CONVERGENCE ALONG STATIONARY FRONT AND DRYLINE WILL BE THE PRIMARY MECHANISMS FORCING TSTM DEVELOPMENT THIS AFTERNOON. LATEST CONVECTION-ALLOWING AND MESOSCALE MODEL GUIDANCE INDICATE THAT THE HIGHEST PROBABILITY OF STORM INITIATION WILL BE ALONG FRONT OVER SRN KS/NRN OK BETWEEN 29/21Z-30/00Z. OTHER ISOLATED STORMS WILL BE POSSIBLE AT THIS TIME SWWD ALONG THE DRYLINE INTO W-CNTRL TX. THE COMBINATION OF STRONG DAYTIME HEATING...BOUNDARY LAYER DEWPOINTS IN THE 60S...AND STEEP MIDLEVEL LAPSE RATES ARE EXPECTED TO YIELD A MODERATE-STRONGLY UNSTABLE AIR MASS BY MID-LATE AFTERNOON WITH MLCAPE VALUES OF 2000-3500 J/KG. WHEN COUPLED WITH A VERTICALLY VEERING WIND PROFILE AND 40-50 KT OF EFFECTIVE BULK SHEAR...SETUP WILL BE QUITE FAVORABLE FOR SUPERCELLS CAPABLE OF VERY LARGE HAIL AND PERHAPS A COUPLE TORNADOES WITHIN THE FIRST FEW HOURS AFTER STORM INITIATION. WITH TIME...CONVECTION-ALLOWING MODEL GUIDANCE IS SUGGESTIVE OF UPSCALE GROWTH INTO A SEWD-MOVING BOW ECHO SYSTEM WHICH WOULD SIGNAL A TRANSITION TO A MORE WIDESPREAD DAMAGING WIND THREAT ACROSS PORTIONS OF OK...PERHAPS INTO NRN TX TONIGHT. ...FL/ERN GA/SRN SC/NC... THE COMBINATION OF A MOIST BOUNDARY LAYER AND BREAKS IN CLOUD COVER WILL YIELD POCKETS OF MODEST DESTABILIZATION TODAY INVOF BERYL. GIVEN A STILL MODESTLY STRONG WIND FIELD...A LOW PROBABILITY RISK FOR DMGG WINDS AND A TORNADO WILL CONTINUE THROUGH THIS AFTERNOON. SEVERAL WEAKER CIRCULATIONS WERE NOTED ACROSS SC THIS MORNING. THIS EVENING INTO TONIGHT...BERYL IS EXPECTED TO DRIFT UP THE COAST...WITH LOW LEVEL VEERING ALONG THE CAROLINA COAST LATE IN THE PERIOD. AN ISOLATED TORNADO REMAINS POSSIBLE AFTER DARK.
via SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_2000.html
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