Heavy Rain in Virginia, July 29, 2001

AREA FORECAST DISCUSSION...UPDATED CCF NUMBERS
NATIONAL WEATHER SERVICE BALTIMORE/WASHINGTON
315 AM EDT SUN JUL 29 2001

UNUSUAL WX SCENARIO FOR JULY OVR THE AREA TDA AND TNGT WITH CLASSIC
COOL AIR DAMMING/OVERRUNNING PATTERN.

SHORTWAVE OVR THE WRN OH VLY AND MID MISS VLY EARLY THIS MORNING WILL
MOVE EWD TDA AND TNGT ALG THE SRN EDGE OF THE WESTERLIES. SHORTWAVE
WILL REACH THE MID ATLC CST THIS EVE THEN MOVE OFFSHR LATE TNGT AND
MON. THE ASSOCD WELL DEFINED SFC LOW WILL TRACK JUST S OF THE CWA TDA
AND TNGT REACHING THE VA CST LATE TNGT THEN MOVE OFFSHR MON. FNT WELL
TO OUR S WILL TRY TO MOVE NWD AS A WMFNT TDA AHD OF THE SFC LOW THEN
SAG SWD AGAIN LATE TNGT AND MON ON THE BACKSIDE OF THE SFC LOW. HIGH
PRES WILL BUILD INTO THE AREA BEHIND THE SFC LOW AND FNT FOR MON. FOR
TUE AND WED...HIGH PRES OVR THE AREA. AVN HAS NEXT FNT APPROACHING FM
THE NW THU NGT/FRI.

CLASSIC COOL AIR DAMMING AND OVERRUNNING SETUP FOR TDA AND TNGT. WELL
DEFINED SFC LOW AND 850MB LOW TRACKING JUST S OF THE CWA TDA AND TNGT
COMBINED WITH DECENT MID LVL DYNAMICS WILL ACT AS A FOCUS FOR PCPN.
MODELS SHOWING IMPRESSIVE UVVS AND ISENTROPIC LIFT/OVERRUNNING OVR THE
AREA AHD OF THE SFC LOW. WARM MOIST SUMMERTIME AIR S OF THE WMFNT WILL
OVERRUN THE UNSEASONABLY COOL AIR WEDGED IN PLACE OVR THE AREA THANKS
TO STG 850MB JET. PWS CLIMB IN EXCESS OF 2 INCHES OVR THE AREA. EXPECT
WIDESPREAD RA TDA INTO EARLY TNGT. WE ARE THINKING 3/4" TO 1" OF RA OVR
THE NRN COUNTIES WITH 1 TO 2 INCHES OVR SRN COUNTIES. WITH SFC LOW AND
SFC FNT REMAINING S OF THE AREA...AIR MASS OVR THE AREA WILL BE QUITE
STABLE AS INDICATED BY THE LIS.  FOR THIS REASON...REMOVED MENTION OF
TSTMS FROM NRN HALF OF THE CWA. COULD BE SOME ELEVATION CONVECTION
EMBEDDED IN THE RA IN THE SRN PORTION OF THE CWA SO LEFT THE MENTION OF
TSTMS IN THOSE ZNS.

EXPECTED QPF AMTS ARE BELOW OUR FFG VALUES...WHICH ARE QUITE HIGH...SO
NO FF WATCH NEEDED.

AVN/ETA SHOW MAIN AREA OF UVVS AND ISENTROPIC LIFT MOVING E OF THE AREA
AFTER 06Z TNGT AS SFC LOW REACHES THE CST. HOWEVER...PLENTY OF MOISTURE
REMAINS OVR THE AREA. SUSPECT PDS OF RA WILL TAPER TO SCT LGT
RA OR DZ LATE TNGT OVR THE CWA W TO E.

ON MON...SFC LOW MOVES OFF THE CST AND SFC FNT WILL SAG SWD ON THE
BACKSIDE OF THE SFC LOW. AVN AND ETA MODELS BOTH SHOW QUITE A BIT OF
LOW LVL MOISTURE IN PLACE IN THE MORNING BUT DYNAMICS...UVVS AND
ISENTROPIC LIFT ARE WELL E OF THE AREA. WILL REMOVE THE POP FOR MON
MORNING. EXPECT M/CLDY SKIES IN THE MORNING BUT EXPECT SOME BINOVC BY
AFTERNOON. WITH DEEPENING SFC LOW OFF THE CST...GRADIENT WILL TIGHTEN
OVR THE AREA SO EXPECT IT WILL BE QUITE BREEZY. MARINE FCST WILL
INDICATE PSBL SCA CONDITIONS OVR OUR SRN WATERS.

M/CLR FOR TUE AND WED WITH HIGH PRES OVR THE AREA. AVN SHOWS SOME
MOISTURE RETURNING ON THU AND THE AVN ALSO SHOWS SOME QPF LATE THU
AHEAD OF THE NEXT FNT. RIGHT NOW WILL INTRODUCE SOME CLOUDS FOR THU BUT
HOLD OFF ON MENTIONING PCPN. CAN'T RULE OUT SCT/ISOLD CONVECTION ON FRI
WITH FNT COMING THRU BUT FOR NOW WILL HOLD ONTO THE DRY FCST AND LET
THE DAY SHIFT TAKE ANOTHER LOOK AT THE THU/FRI FCST.

FOR TEMPS...NGM AND AVN MOS SEEM TO HAVE A GOOD HANDLE ON THE COOL AIR
DAMMING TDA SO MOS MAX TEMPS ACCEPTED. NGM AND AVN MOS ARE CLOSE 2ND PD
AND ACCEPTED. WENT WITH THE COOLER NGM MOS NUMBERS FOR MON GIVEN THE
FACT THAT MOS HAS BEEN RUNNING TOO HIGH WITH MAX TEMPS LATELY.

COORDINATED WITH RNK AND AKQ.

FCSTID = 15 / DMW

DCA   68  63  78  65 / 100 80  20   0
BWI   68  61  77  61 / 100 80  20   0
MRB   67  60  78  60 / 100 80  10   0
IAD   67  61  78  59 / 100 80  10   0
CHO   67  62  78  62 / 100 80  10   0
HGR   67  59  77  58 / 100 80  10   0
NHK   69  63  77  64 / 100 80  20   0
W99   67  58  78  57 / 100 80  10   0

.LWX...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...NONE.