Severe Thunderstorm Warning 263, NWS Baltimore/Washington

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
434 PM EDT SUN JUL 3 2011

.SYNOPSIS...
A COLD FRONT WILL PASS THROUGH THE REGION TONIGHT BEFORE STALLING IN
SOUTHERN VIRGINIA. SHOWERS AND THUNDERSTORMS ARE EXPECTED ALONG AND
AHEAD OF THE FRONT. HIGH PRESSURE WILL BUILD BRIEFLY ON TUESDAY. THE
STALLED FRONT WILL MOVE NORTHWARD MID-WEEK AS A WARM FRONT.

&&

.NEAR TERM /THROUGH MONDAY/...
UPDATED FORECAST TO ADD WATCH AND TO RAISE AFTERNOON/EVE POPS.
PREVIOUS DISCUSSION BELOW.

A QUIET MORNING ACROSS THE MID ATLC HAS BEEN BREWING AN ATMOSPHERE
THAT WILL LIKELY BE FILLING IN WITH SCATTERED SHOWERS AND TSTMS OVER
THE NEXT FEW HRS. THE COLD FRONT REMAINS BACK ACROSS THE OHIO VLY
AND INTO CNTRL PA BUT IS MAKING A STEADY JOG TOWARD THE ESE. IN
THE NEXT 3-4 HRS /LATE AFTN/...THE FRONT WILL MAKE AN APPEARANCE
OVER THE POTOMAC HIGHLANDS. BY THIS TIME...AT LEAST SEVERAL
BATCHES OF SHOWER AND TSTMS WILL HAVE DEVELOPED ACROSS NRN AND WRN
PORTIONS OF THE CWA...MAKING THEIR WAY TOWARD THE SE.

INSTABILITY IS PLENTIFUL WITH TEMPS ALREADY AT OR NEAR THE NECESSARY
CONVECTIVE SFC TEMP TO BREAK THE LOW-LEVEL CAPPING INVERSION /L-M90S/.
FROM THERE...STEEP LOW- AND MID-LEVEL LAPSE RATES EXIST...NEAR
7.0-7.5 C/KM...WHICH SHOULD ENHANCE A FEW UPDRAFTS TO REACH SEVERE
LEVELS...ALONG WITH NEARLY 3000-3500 J/KG OF CAPE. DAMAGING WET
MICROBURSTS AND LARGE HAIL POSSIBLE WITH THE STRONGEST ACTIVITY.
BRIEF HEAVY DOWNPOURS POSSIBLE WITH ANY CELLS...SO FLASH FLOODING
POTENTIAL ALSO EXISTS FROM THE POTENTIALLY HIGH RAIN RATES AND
PWATS ABOVE 2 INCHES.

A NUMBER OF WEAK OUTFLOW BOUNDARIES FROM THE OVERNIGHT TSTM ACTIVITY
ALONG WITH THE INCOMING FRONTAL BOUNDARY AND LEE TROUGH WILL BE
ENOUGH FOR INITIATION THIS AFTN. SHEAR WILL BE LOW HOWEVER...SO
INDIVIDUAL CELLS WILL NOT LAST LONG BUT ACT TO CREATE OUTFLOW FOR
SUBSEQUENT NEARBY DEVELOPMENT. AS MORE ORGANIZED OUTFLOW
DEVELOPS...STORMS LIKELY WILL FORM A LINE THAT WILL PUSH ACROSS
THE REMAINDER OF THE CWA INTO THE EVE HRS. THE METRO AREAS ALONG
I-95 THEN DOWN INTO THE CHARLOTTESVILLE AREA /AND AREAS TO THE
SOUTH AND EAST/ WILL BE THE MORE LIKELY PLACES FOR THE STRONGEST
ACTIVITY ONCE THE LINE DEVELOPS.

LOCAL MODEL GUIDANCE HAS BEEN FAIRLY CONSISTENT IN DEVELOPING A
CONVECTIVE LINE...MAINLY WITH TIMING AND MINOR PLACEMENT DIFFERENCES
FROM RUN TO RUN. ALREADY...A CONVECTIVE LINE IS FORMING ACROSS THE
MASON-DIXON LINE FROM N CNTRL MD TO THE NRN WV PANHANDLE /ALONG
THE OHIO RVR/.

THE FRONT WILL HELP PUSH THE REMNANTS OF THE SHOWERS/TSTMS TOWARD
THE SE AND AWAY FROM THE MID-ATLC LATER THIS EVE...CLOSER TO SUNSET
AND AFTER. INTO THE LATE NIGHT HRS...ONLY SOME LEFTOVER SHOWERS
AND BRIEF TSTMS WILL CONTINUE TO DEVELOP IN THE STILL WEAKLY
UNSTABLE AIRMASS. AFTER A BULK OF THE ACTIVITY HAS MOVED AWAY...
MOST OF THE AREA WILL HAVE BEEN AT LEAST SOMEWHAT RAIN-COOLED WITH
TEMPS BACK INTO THE 70S AND L80S. OVERNIGHT LOWS HOWEVER WILL ONLY
DROP A FEW MORE DEGREES FROM THERE AS THE AIRMASS CHANGES ONLY
SLIGHTLY. DEWPOINTS WILL DROP A FEW DEGREES...BUT WILL STAY IN THE
L-M60S.

SOME UPPER-CLOUD DEBRIS FROM THE OHIO VLY STORMS WILL MOVE THROUGH
OVERNIGHT BUT MOST OF THE AREA SHOULD BE MOSTLY CLEAR-PARTLY
CLOUDY INTO EARLY MONDAY. STILL EXPECTING I-66 TO BE A ROUGH
DIVIDING LINE FOR PRECIP...THOUGH NEAR TERM GUIDANCE /ESPECIALLY
THE MOST RECENT NAM RUNS/ HAS BEEN DEVELOPING A BATCH OF AFTN
TSTMS ACROSS THE LOWER POTOMAC HIGHLANDS THAT WOULD THEN TRACK
SEWD...PASSING SOUTH AND EAST OF THE METRO DC AREA BEFORE
DISSIPATING ACROSS CNTRL VA. ADDED CHANCE POPS TO THESE WRN ZONES...
SINCE AN UPPER LEVEL VORT MAX WILL BE COMING ACROSS THE CNTRL
APLCNS AT THAT PERIOD IN TIME.

KEPT POPS OUT OF THE DC METRO AREA...WITH AN OUTSIDE CHANCE OF AN
ISOLATED AND SHORT-LIVED CELL NEAR THE AREA LATE AFTN-EVE. THE
UPPER LEVEL TROUGH WILL CONTINUE TO SLIDE OVER THE REGION MON
NIGHT INTO TUE...KEEPING AT LEAST A LOW CHANCE OF PRECIP OVER THE
SRN HALF OF THE AREA.

&&

.SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
FRONTAL BNDRY WILL RMN IN SRN VA MON NGT-TUE NGT. DESPITE THE FCST
AREA BEING N OF BNDRY...MSTR WILL BE PLENTIFUL. WITH SVRL LOW-
AMPLITUDE SHRTWV TROFS MOVG ACRS...SHWRS AND PSBLY A FEW TSTMS
CANNOT BE RULED OUT. BEST CHC FOR PCPN WILL BE ALONG AND JUST N OF
THIS BNDRY...AND POP GRIDS WERE ADJUSTED ACCORDINGLY.

MAXIMA WILL BE IN THE UPR 80S-NR 90 ON TUE. OWING TO HIGH BNDRY
LYR DEWPTS...MINIMA WILL BE IN THE MID 60S-LWR 70S BOTH NGTS.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
STALLED BNDRY IN SRN VA WILL BGN TO LIFT NWD ON WED...RETURNING
FCST AREA TO THE WARM SECTOR. FAIRLY ACTIVE NRN JET STREAM WILL
MAINTAIN A TRAIN OF SHRTWV TROFS THAT WILL IMPACT THE FCST AREA
THRU THE WK. CDFNT WILL CROSS THE RGN BY THU EVE...WITH MODEST
HIPRES BUILDING LATE IN THE WK ACCOMPANIED BY PSBL ONSHORE FLOW.

&&

.AVIATION /21Z SUNDAY THROUGH FRIDAY/...
CBS WILL BEGIN TO APPEAR FROM WEST TO EAST IN THE 19-21Z TIME
PERIOD FROM THE CNTRL APLCNS TO THE BAY. SCATTERED TSTMS ARE
EXPECTED TO DEVELOP ACROSS THE NRN SHENANDOAH VLY AND INCREASE IN
COVERAGE AS THEY MOVE TOWARD THE METRO AREAS LATE AFTN-EVE /BEFORE
00Z/. CLOSER TO AND JUST AFTER 00Z...THE ACTIVITY IS EXPECTED TO
BE LEAVING THE METRO AREAS AND MOVING ACROSS SRN MD. BEHIND THIS
ACTIVITY WILL BE SCATTERED SHOWERS INTO EARLY MRNG HRS. A PERIOD
OF MVFR FOG POSSIBLE IN THE PREDAWN HRS.

MON MORNING SHOULD BE QUIET AGAIN LIKE THIS MORNING...WITH ONLY
ISOLATED SHOWERS/TSTMS SOUTH OF I-66 MON AFTN/EVE. THIS ACTIVITY
WILL ALSO DRIFT SE AND OUT OF THE AREA INTO THE LATE NIGHT HRS.

MAIN CONCERN FOR ANY FLIGHT RESTRICTIONS MON NGT-THRU FRI WILL BE
FROM ANY TSTMS. BEST CHC FOR PCPN AT TERMINALS WILL BE WED AFTN-
EVE AND THU AFTN-EVE.

&&

.MARINE...
WINDS GENERALLY LESS THAN 15KT WITH MOST AREAS ALONG THE MAIN
CHANNEL OF THE BAY AT 10KT. THE ONLY SCA THRESHOLD CONDITIONS /OR
WORSE/ EXPECTED TO BE WITH LOCALIZED TSTM ACTIVITY. GUSTY WINDS AND
SMW-TYPE CONVECTION EXPECTED LATE THIS AFTN-EVE WITH A LINE OF
STORMS MOVING TOWARD THE SE. LIGHT WINDS RETURN OVERNIGHT...AND A
GENERAL WNWLY FLOW NEAR 10 KT DEVELOPS MON AFTN. NO MARINE
HEADLINES XPCD FOR RMNDR OF FCST PD.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...NONE.

&&

UPDATE...LISTEMAA

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