Saturday, December 22, 2007
Saturday Evening Update
Strange to say this right before Christmas, but there could be some severe weather on Sunday. Below is the discussion from the Storm Prediction Center:
...MID ATLANTIC REGION... THERE IS SOME CONCERN WITH RESPECT TO THE DEGREE OF MOISTURE RETURN OFF OF THE ATLANTIC AS SLY WINDS STRENGTHEN ON SUNDAY AHEAD OF THE DEEPENING UPPER LOW ACROSS THE GREAT LAKES REGION. HOWEVER... SURFACE DEWPOINTS IN THE LOWER 60S RESIDE AT THIS TIME ABOUT 100-130 MILES OFF THE SRN ATLANTIC COAST. THIS MOISTURE SHOULD ADVECT NWD TO AT LEAST NRN NC BY SUNDAY AFTERNOON WITH UPPER 50S DEWPOINTS INTO VA/DELMARVA REGION. COOLING ALOFT ATTENDANT TO HEIGHT FALLS WITH APPROACHING UPPER SYSTEM/ASCENT WITHIN ENTRANCE REGION OF UPPER LEVEL JET COMBINED WITH LOW LEVEL WARM AIR/MOISTURE ADVECTION WILL SUPPORT MARGINAL INSTABILITY...BELOW 500 J/KG. DYNAMIC LIFT ASSOCIATED WITH THE ARKLATEX/TN VALLEY SHORT WAVE TROUGH...COUPLED WITH LOW LEVEL WAA...SHOULD SUPPORT DEVELOPMENT OF A LOW-TOPPED SQUALL LINE WITH RAPIDLY MOVING/BOWING LINE SEGMENTS. MAGNITUDE OF FORCING/LIFT ALONG THE ADVANCING FRONT WITH WEAK INSTABILITY SHOULD SUPPORT SPORADIC LIGHTNING. GREATEST POTENTIAL FOR BOUNDARY LAYER MODIFICATION/COUPLING WILL EXIST EAST OF THE APPALACHIANS WHERE DEVELOPMENT OF A NARROW COLD FRONTAL RAIN BAND APPEARS LIKELY DURING THE AFTERNOON. KINEMATICS AS CURRENTLY FORECAST APPEAR MORE THAN SUFFICIENT FOR CONVECTIVE DAMAGING WINDS TO SPREAD EAST THROUGH EARLY EVENING GIVEN FORECAST STORM MOTION OF 50-60KT...AND MEAN WIND IN EXCESS OF 70KT. A BRIEF/ISOLATED TORNADO CANNOT BE COMPLETELY RULED OUT GIVEN INTENSE EFFECTIVE SRH IN EXCESS OF 400-500 M2/S2 OVER SOME PARTS OF ERN VA TO THE DELMARVA/SERN PA AREA THROUGH EARLY EVENING. ¶ 5:36 PM
...MID ATLANTIC REGION... THERE IS SOME CONCERN WITH RESPECT TO THE DEGREE OF MOISTURE RETURN OFF OF THE ATLANTIC AS SLY WINDS STRENGTHEN ON SUNDAY AHEAD OF THE DEEPENING UPPER LOW ACROSS THE GREAT LAKES REGION. HOWEVER... SURFACE DEWPOINTS IN THE LOWER 60S RESIDE AT THIS TIME ABOUT 100-130 MILES OFF THE SRN ATLANTIC COAST. THIS MOISTURE SHOULD ADVECT NWD TO AT LEAST NRN NC BY SUNDAY AFTERNOON WITH UPPER 50S DEWPOINTS INTO VA/DELMARVA REGION. COOLING ALOFT ATTENDANT TO HEIGHT FALLS WITH APPROACHING UPPER SYSTEM/ASCENT WITHIN ENTRANCE REGION OF UPPER LEVEL JET COMBINED WITH LOW LEVEL WARM AIR/MOISTURE ADVECTION WILL SUPPORT MARGINAL INSTABILITY...BELOW 500 J/KG. DYNAMIC LIFT ASSOCIATED WITH THE ARKLATEX/TN VALLEY SHORT WAVE TROUGH...COUPLED WITH LOW LEVEL WAA...SHOULD SUPPORT DEVELOPMENT OF A LOW-TOPPED SQUALL LINE WITH RAPIDLY MOVING/BOWING LINE SEGMENTS. MAGNITUDE OF FORCING/LIFT ALONG THE ADVANCING FRONT WITH WEAK INSTABILITY SHOULD SUPPORT SPORADIC LIGHTNING. GREATEST POTENTIAL FOR BOUNDARY LAYER MODIFICATION/COUPLING WILL EXIST EAST OF THE APPALACHIANS WHERE DEVELOPMENT OF A NARROW COLD FRONTAL RAIN BAND APPEARS LIKELY DURING THE AFTERNOON. KINEMATICS AS CURRENTLY FORECAST APPEAR MORE THAN SUFFICIENT FOR CONVECTIVE DAMAGING WINDS TO SPREAD EAST THROUGH EARLY EVENING GIVEN FORECAST STORM MOTION OF 50-60KT...AND MEAN WIND IN EXCESS OF 70KT. A BRIEF/ISOLATED TORNADO CANNOT BE COMPLETELY RULED OUT GIVEN INTENSE EFFECTIVE SRH IN EXCESS OF 400-500 M2/S2 OVER SOME PARTS OF ERN VA TO THE DELMARVA/SERN PA AREA THROUGH EARLY EVENING. ¶ 5:36 PM
