MESOSCALE DISCUSSION 1362
NWS STORM PREDICTION CENTER NORMAN OK
0535 PM CDT TUE JUN 27 2006
AREAS AFFECTED...PORTIONS SERN AND EXTREME E-CENTRAL
VA...CENTRAL/SRN MD...DC...DE...EXTREME SERN PA.
CONCERNING...SEVERE THUNDERSTORM POTENTIAL...HEAVY RAINFALL
VALID 272235Z - 280100Z
POTENTIAL MAY BE INCREASING OVER DISCUSSION AREA FOR SUPERCELLS AND
SHORT-LIVED TORNADOES. AREA WILL BE MONITORED FOR POSSIBLE WW.
SRN BOUND OF MOST FAVORABLE AREA WILL BE DEFINED BY LOW-MIDLEVEL
CYCLONE LIFTING NNEWD ACROSS NERN NC. THIS FEATURE IS EXPECTED TO
MOVE NNEWD 20-25 KT ACROSS NERN NC...SERN VA AND SRN
CHESAPEAKE/DELMARVA REGION THROUGH NEXT 4-6 HOURS. MESOBETA SCALE
ENHANCEMENTS IN LOW-MIDLEVEL SHEAR AND LIFT ARE EXPECTED WITHIN
ABOUT 150 NM NNW-NE OF THIS CYCLONE...WITH JUST ENOUGH BACKING OF
SFC FLOW AND INCREASE IN SPEEDS THROUGH LOWEST KM AGL TO YIELD SRH
100-200 J/KG IN THAT LAYER...BASED ON MODIFIED VWP AND RUC FCST
SOUNDINGS. FARTHER N...VIS IMAGERY SHOWS PRONOUNCED LOW CLOUD BAND
FROM ABOUT 36N73.5W NNWWD ACROSS DE BAY AND SRN NJ COAST. THIS
DENOTES CHANGE IN MARINE AIR MASS AND SFC THETAE -- EVIDENT IN 70S F
SFC DEW POINTS ACROSS CHESAPEAKE BAY REGION AND MID 60S NJ COAST.
GREATEST HEAVY RAIN AND SVR POTENTIAL SHOULD REMAIN W OF NNWWD
EXTRAPOLATION OF THIS BAND AND E OF I-95 WHERE SHEAR IS RELATIVELY
MAXIMIZED. THERMODYNAMICALLY...AIR MASS SW OF CLOUD BAND IS
TROPICAL IN CHARACTER WITH WEAK MIDLEVEL LAPSE RATES...OFFSET ENOUGH
BY VERY RICH LOW LEVEL MOISTURE AND WEAK CINH TO YIELD MLCAPES
500-800 J/KG. ONLY GRADUAL DECREASE IN BUOYANCY IS EXPECTED AFTER
DARK BECAUSE OF CONVECTIVE OUTFLOWS AND WEAK SFC COOLING...STILL
OFFSET BY AMPLE AMBIENT MOISTURE.
HEAVY RAIN POTENTIAL WILL BE ENHANCED WITH APCH OF LOW AS WELL. VERY
EFFICIENT WARM-CLOUD PRECIP PROCESSES ARE EXPECTED THROUGH LARGE
SUBSET OF CONVECTIVE CLOUD LAYER...RESULTING IN 1.5-2.5 INCH/HOUR
RAIN RATES IN HEAVIEST CORES. TRAINING/MERGING OF CONVECTIVE CELLS
AND CLUSTERS WILL LOCALLY MAXIMIZE THIS THREAT.
..EDWARDS.. 06/27/2006