Flash Flooding and Hail in Virginia, July 23, 2002

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE/WASHINGTON
200 PM EDT TUE JUL 23 2002

SHORT TERM...TNGT THRU WED NIGHT...

HUGE SUBTROPICAL RIDGE WILL CONTINUE TO DOMINATE A GOOD PORTION OF
THE NATION WITH ITS CENTER REMAINING OVR THE WRN STATES.
MEANWHILE...THE WESTERLIES WILL RIDE OVR THE UPR LVL RIDGE ALONG THE
U.S./CANADIAN BORDER TO NEW ENGLAND. THERE WILL BE A TENDENCY FOR
SOME WEAK TROFFINESS IN THE ERN STATES. IN THIS PATTERN...OUR AREA
WILL BE ON THE SOUTHERN EDGE OF THE WESTERLIES. AS HGTS LOWER A BIT
TNGT AND WED...A COLD FRONT WILL PUSH SEWD INTO THE AREA. HOWEVER...
AS IT REACHES THE SRN EDGE OF THE WESTERLIES ON WED...IT WILL BECOME
PARALLEL TO THE UPR LVL FLOW AND BECOME QUASI-STATIONARY OVR THE
AREA AND REMAIN THERE WELL BEYOND THE SHORT TERM.

AT 18Z CDFNT EXTENDED FM CENTRAL NY THRU WRN PA THEN BACK THRU THE
OH VLY. FRONT WILL PRESS SWD INTO THE AREA TNGT. DYNAMICS REMAIN
WELL N OF THE AREA AND BEST WIND FIELDS/SHEAR REMAIN N OF THE AREA
SO BEST CHC OF ORGANIZED SVR WX WILL BE TO OUR N WHERE BOXES ARE
CURRENTLY POSTED. MODIFIED SOUNDING GIVES IAD AN LI OF -5C AND OVR
3000 J/KG THIS AFTRN AND EARLY EVENING SO INSTABILITY WILL BE
PRESENT. EXPECT SCT SHRA/TSRA TO FORM IN THE INSTABILITY  DURING
THE REMAINDER OF THE AFTRN AND EVENING WITH A LINE OF CONVECTION
POSSIBLE THIS EVENING ALG THE PREFRONTAL TROF. WITH GOOD
INSTABIILITY...A FEW/ISOLD PULSE SVR STORMS ARE NOT OUT OF THE
QUESTION LATE THIS AFTRN INTO THIS EVE BUT AS STATED ABOVE...THE
BEST CHC OF ORGANIZED SVR WILL BE TO OUR N. PCP H20 IS NEARLY 2
INCHES OVR THE AREA SO STORMS COULD PRODUCE SOME VERY HEAVY RAIN.
HOWEVER...STORMS SHOULD BE MOVING ALG AT LEAST 15 KTS SO DONT
EXPECT ANY ONE STORM TO STAY OVR ANY ONE LOCATION FOR VERY LONG. NO
FFA BUT LOCALIZED FLOODING IN LOW LYING AND POOR DRAINAGE AREAS
CERTAINLY POSSIBLE.  WILL KEEP LIKELY POPS GOING ALL NIGHT AS CDFNT
WILL BE IN THE AREA AND WEAK WAVES MOVE ALG THE FNT.

WITH QUASI-STATIONARY FNT OVR THE AREA WED AND WED NIGHT AND PLENTY
OF MOISTURE IN PLACE...WILL GO WITH CHC POPS FOR SHRA/TSRA.

WILL LET THE HEAT ADVY GO FOR A FEW MORE HOURS (6PM) UNTIL HEATING
STARTS TO DIMINISH THEN EVE SHIFT CAN UPDATE.

NGM/AVN AND ETA MOS TEMP FCST ARE CLOSE WITH THE ETA BEING A BIT
WARMER THAN THE AVN/NGM FOR MAX TEMPS ON WED. LEANED TOWARD THE
SLIGHTLY COOLER AVN/NGM WITH ONLY MINOR ADJUSTMENTS.

WALSTON

LONG TERM (THURS-TUE)

STATIONARY SFC FRONT WILL BE JUST SOUTH OF THE AREA THURS MORNING.
MODEL PROGS INDICATE CLOUDS WILL LINGER MUCH OF THE DAY ESPECIALLY
FROM WASHINGTON SOUTH WHICH WILL KEEP TEMPS DOWN MUCH OF THE DAY.
HAVE KEPT CHANCE OF SHRA/TSRA FOR THURS BUT THINK ANY SHRA ACTIVITY
WILL BE CONFINED TO THE SOUTHERN PORTION OF OUR CWA. FRONT WILL
RETURN BACK AS A WARM FRONT FRI MORNING WHILE A SFC LOW PRESSURE
DEVELOPS ALNG THE FRONT.  COULD BE SOME MORNING SHOWERS/TSRA AROUND
THE AREA WITH AIR MASS DRYING OUT A BIT DURING THE AFTERNOON AND
HIGH PRESSURE BUILDING ACROSS THE REGION.  SATURDAY...WEAK FRONT
REMAINS ALONG THE MASON/DIXON LINE WITH LEE SIDE TROF DEVELOPING
DURING THE AFTERNOON...WITH PLENTY OF MOISTURE AND INSTABILITY AND A
WEAK SHORTWAVE-TROUGH MOVING INTO THE AREA...HAVE INTRODUCED CHANCE
POPS FOR ALL AREAS.  SUBSIDENCE/DRY AIR STARTS TO FILTERS IN BEHIND
DEPARTING SHORTWAVE FOR A NICE DAY ON SUNDAY. MON/TUE APPEARS DRY
WITH ONLY SILENT 20 POPS.

ROSA

.LWX...
DC...HEAT ADVISORY UNTIL 6 PM TODAY FOR ZONE DCZ001.
MD...HEAT ADVISORY UNTIL 6 PM TODAY FOR ZONES
     MDZ002>007...MDZ009>011...MDZ013>014...MDZ016>018.
VA...HEAT ADVISORY UNTIL 6 PM TODAY FOR ZONES
     VAZ025>031...VAZ036>042...VAZ050>057.
WV...HEAT ADVISORY UNTIL 6 PM TODAY FOR ZONES WVZ048>053...WVZ055.