This is the latest storm update from the National Weather Service. I will update the forecast map on the next posting.
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0301 PM CDT SAT SEP 08 2012 VALID 082000Z - 091200Z ...THERE IS A MDT RISK OF SVR TSTMS INTO THE EVENING FROM FAR NERN MD/NRN DE ACROSS FAR ERN PA..NJ...ERN NY AND WRN NEW ENGLAND... ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK...FROM NRN NEW ENGLAND TO THE CAROLINAS... ...NORTHEAST AND MID ATLANTIC REGION THROUGH TONIGHT... GIVEN TRENDS IN REGIONAL RADAR IMAGERY FROM ERN NY THROUGH ERN PA TO FAR NRN MD SHOWING THE COLD FRONT MERGING WITH AND OVERTAKING THE PRE-FRONTAL SQUALL LINE...THE WRN EXTENTS OF THE MODERATE AND SLIGHT RISK AREAS AND SEVERE PROBABILITIES HAVE BEEN SHIFTED EWD. SPECIAL 18Z SOUNDINGS AT ALBANY AND UPTON NY BOTH OBSERVED AN INCREASE IN KINEMATICS AS COMPARED TO FARTHER S AT STERLING VA AND AS FORECAST IN THE EARLIER FORECASTS FOR THIS REGION. THUS...THE POTENTIAL FOR PRE-FRONTAL TORNADO THREAT WILL CONTINUE BOTH WELL AHEAD OF THE COLD FRONT WITHIN WW/S 635 AND 637...AND WITH EMBEDDED CIRCULATIONS WITH THE SQUALL LINE. OTHERWISE...THE RISK FOR DAMAGING WINDS WILL PERSIST ALONG THE PROGRESSIVE EWD MOVING SQUALL LINE ACROSS THE MODERATE AND SLIGHT RISK AREAS. ..PETERS.. 09/08/2012 .PREV DISCUSSION... /ISSUED 1106 AM CDT SAT SEP 08 2012/ ...NORTHEAST AND MID ATLANTIC THROUGH TONIGHT... A STRONG MIDLEVEL SHORTWAVE TROUGH WILL EJECT EWD THIS MORNING AND THEN NEWD THIS AFTERNOON/EVENING OVER THE APPALACHIANS AND NEW ENGLAND...AS AN UPSTREAM WAVE DIGS SEWD OVER THE UPPER MS VALLEY. THE EJECTING WAVE WILL BE ACCOMPANIED BY A DEEPENING SURFACE CYCLONE ACROSS THE SAINT LAWRENCE VALLEY...AND A COLD FRONT WHICH WILL SWEEP EWD ACROSS THE APPALACHIANS THIS AFTERNOON...REACHING THE ATLANTIC COAST TONIGHT. A MOIST LOW-LEVEL AIR MASS IS PRESENT IN ADVANCE OF THE COLD FRONT...WITH BOUNDARY LAYER DEWPOINTS RANGING FROM THE MID 60S ACROSS MUCH OF NY/NEW ENGLAND TO THE LOW 70S ACROSS THE MID ATLANTIC COAST. DESPITE MIDLEVEL LAPSE RATES NEAR 6 C/KM...THE OBSERVED LOW-LEVEL MOISTURE AND SOME SURFACE HEATING IN PRE-FRONTAL CLOUD BREAKS WILL SUPPORT SOME DESTABILIZATION AND THE POTENTIAL FOR AFTERNOON MLCAPE OF 500-1500 J/KG. THE DEEPENING SURFACE CYCLONE AND EJECTING MIDLEVEL WAVE WILL RESULT IN THE EWD EXPANSION OF A STRONG VERTICAL SHEAR ENVIRONMENT ACROSS THE NRN MID ATLANTIC/NY/WRN NEW ENGLAND THROUGH THIS EVENING. FORECAST HODOGRAPHS INVOF THE HUDSON VALLEY ARE FAVORABLE FOR SUPERCELLS WITH SUBSTANTIAL LENGTH /EFFECTIVE BULK WIND DIFFERENCES AOA 50 KT/ AND LOW-LEVEL CURVATURE /EFFECTIVE SRH OF 250-350 M2 PER S2/. THERE WILL BE SOME POTENTIAL FOR PRE-FRONTAL SUPERCELLS WITH AT LEAST AN ISOLATED TORNADO RISK ALONG THE AXIS OF LOW 70S DEWPOINTS AND STRONGER SURFACE HEATING FROM NRN NJ ACROSS SE NY...WRN CT...AND WRN MA THIS AFTERNOON AS LOW-LEVEL SHEAR INCREASES. FARTHER W...THE DEGREE OF BUOYANCY AND STRONG LINEAR ASCENT ALONG THE COLD FRONT BOTH SUGGEST THAT THE PREDOMINANT CONVECTIVE MODE WILL BE LINEAR. STILL...A FEW TORNADOES WILL BE POSSIBLE WITH EMBEDDED CIRCULATIONS IN THE LINE /OR ANY SUSTAINED CELLS AHEAD OF THE LINE THIS AFTERNOON/...ALONG WITH WIDESPREAD DAMAGING WINDS ACROSS ERN PA/NY/WRN NEW ENGLAND THROUGH LATE EVENING. A BAND OF THUNDERSTORMS WILL ALSO DEVELOP FARTHER S ALONG THE COLD FRONT THIS AFTERNOON INTO VA AND THE CAROLINAS. WIND PROFILES WILL NOT BE AS STRONG AS AREAS FARTHER TO THE N...BUT SCATTERED DAMAGING GUSTS CAN STILL BE EXPECTED. ...WI LATE THIS AFTERNOON... A STRONG SHORTWAVE TROUGH WILL DIG SEWD OVER WI LATER TODAY. SURFACE HEATING AND A PRONOUNCED BAND OF ASCENT COULD LEAD TO THE DEVELOPMENT OF WEAK SURFACE-BASED INSTABILITY THIS AFTERNOON...AND AN ATTENDANT RISK FOR A FEW THUNDERSTORMS. STRONG GUSTS COULD ACCOMPANY SOME OF THESE STORMS GIVEN STEEP LOW-LEVEL LAPSE RATES AND STRONG MIDLEVEL FLOW...AS WELL AS SMALL HAIL.
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