Severe Thunderstorm Warning 166, NWS Baltimore/Washington

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
323 PM EDT FRI JUN 26 2009

.SYNOPSIS...
A WEAK LOW PRESSURE TROF WILL CREATE UNSTABLE CONDITIONS ACROSS THE
MID ATLANTIC REGION THIS AFTERNOON. HIGH PRESSURE WILL BUILD OVER
THE REGION INTO SUNDAY. ANOTHER UPPER LEVEL LOW WILL AFFECT THE
REGION FOR MUCH OF NEXT WEEK...AFTER A COLD FRONT PASSAGE ON
SUNDAY...AND MODERATED TEMPS AND LOW CHANCES FOR PRECIPITATION
THROUGH THE MIDDLE OF THE WEEK.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
1830Z WV IMAGERY DEPICTS LOW ENTERING QUEBEC. ATTENDANT COLD
FRONT DEPICTED IN REGIONAL SFC OBS OVER LAKE ONTARIO EXTENDING SW
ACROSS WRN PA AND ERN OH. CONVECTIVELY DRIVEN ISOLATED
THUNDERSTORMS HAVE POPPED ACROSS NRN MD AND ALONG THE WRN RIDGES
AHEAD OF THE FRONT. EXPECT FURTHER DEVELOPMENT WITH MORE INTENSE
MULTICELLS THROUGH THE REST OF THE AFTERNOON AND INTO THE EVENING
HOURS AS THE COLD FRONT APPROACHES. CAPE VALUES OF 2000 TO 2500
J/KG...BULK SHEAR VALUES 30 TO 35 KT COULD ENABLE SOME DISCRETE
SUPERCELL STRUCTURES...PARTICULARLY NORTHERN HALF OF CWA WHERE
BETTER WINDS /CLOSER TO PARENT SYSTEM/ ARE PRESENT. DAMAGING WIND
IS THE MAIN CONCERN WITH MARGINALLY SEVERE HAIL ALSO POSSIBLE. A
SEVERE THUNDERSTORM WATCH HAS BEEN POSTED FOR ROUGHLY THE NORTHERN
HALF OF THE CWA UNTIL 10 PM. PLEASE VISIT OUR WEBSITE
WWW.WEATHER.GOV/LWX FOR FURTHER DETAILS.

FROPA TONIGHT ENDS PRECIP CHANCES FROM NW TO SE. MAY SEE ACTIVITY
LINGER THROUGH MIDNIGHT...PARTICULARLY SOUTHERN MARYLAND AND ALONG
THE CHES BAY. EXPECT SEVERE THREAT TO DIMINISH AFTER SUNSET...THOUGH
STORMS WITH STRONG/GUSTY WINDS COULD CONTINUE.

QUICK CLEARING BEHIND THE FRONT FROM SUBSIDENCE AND DOWNSLOPING
WINDS. PATCHY FOG...PARTICULARLY WHERE SUBSTANTIAL RAIN FALLS IS
CERTAINLY POSSIBLE TOWARDS SUNRISE. GIVEN SCATTERED NATURE OF THE
PRECIP AND LIMITING FACTOR OF WINDS...DID NOT WANT TO BLANKET THE
AREA WITH PATCHY FOG GRIDS.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
SUBSIDENCE...NWLY WINDS...SUNNY SKIES...AND DEWPOINTS AROUND 60F
WILL MAKE FOR ABOUT AS IDEAL A SATURDAY FOR LATE JUNE /WHICH USUALLY
FEATURES HIGHER DEWPOINTS/. MAX TEMPS IN THE M80S /U80S/.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
FCST AREA RMNS ON W SIDE OF UPR TROF SAT NGT AS SHRTWV RDGG
APRCHS. A SHRTWV TROF MOVES SEWD JUST BEHIND UPR RDG AND XPCD TO
IMPACT AREA ON SUN. HAVE INCRD POPS SUN AFTN AND EVE...SPCLY NRN
SECTIONS AS WAVE MOVES ACRS PA.

EXTENDED PDS CHARACTERIZED BY UNSEASONABLY DEEP CLOSED UPR LOW
OVER ERN CONUS. THIS POSITION SHUD RESULT IN BLW NRML MAXIMA /MID
70S TO LWR 80S/ AND PSBLTYS OF PCPN THRU MUCH OF NEXT WEEK AS SVRL
SHRTWV TROFS MOVE AROUND PERIPHERY OF UPR LOW.

SYSTEM FCST TO EXIT BY LATE NEXT WK...WITH MODERATING TEMPS XPCD.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
COLD FRONT APPROACHES FROM THE NW THIS EVENING WITH PREFRONTAL
THUNDERSTORMS...SOME SEVERE POSSIBLE /DAMAGING WINDS MAIN
THREAT...PARTICULARLY ALONG AND NORTH OF A LINE FROM KADW TO KDCA TO
KW99/ UNTIL MIDNIGHT. CB BASES CURRENTLY AROUND 5KFT WITH POSSIBLE
IFR VSBYS/MVFR CIGS WITH TSTMS. VFR RETURNS TONIGHT AFTER FROPA AND
CONTINUES THROUGH SATURDAY UNDER SUBSIDENCE...BUILDING HIGH PRESSURE.

DRY WX ON SAT WITH MINIMAL AVIATION IMPACTS...BUT RETURN TO
SHRA/TSRA PSBL BY SUN AFTN...SPCLY NRN TERMINALS.

&&

.MARINE...
COLD FRONT APPROACHES FROM THE NW THIS EVENING WITH PREFRONTAL
THUNDERSTORMS...SOME SEVERE POSSIBLE ACROSS THE WATERS UNTIL
MIDNIGHT. MAIN THREAT IS DAMAGING WINDS WITH SMW/S LIKELY. FRONT
PUSHES THROUGH TONIGHT WITH NWLY WINDS TOMORROW. GRADIENT DOES NOT
LOOK STRONG ENOUGH FOR SCA TOMORROW...EXPECT 10 TO 15 KT OVER THE
WATERS. CANNOT RULE OUT ISOLATED GUSTS TO 20 KT.

SMALL CRAFT ADZY CONDITIONS PSBL SUN AS CDFNT MOVES THRU...BUT
OTHERWISE WINDS XPCD TO RMN BLW CRITERION DURG MOST OF FCST PCKG.

&&

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

&&

BAJ/KRAMAR

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
329 PM EDT FRI JUN 26 2009

ANZ530>537-DCZ001-MDZ006-007-011-013-014-016>018-VAZ052>057-
271000-
CHESAPEAKE BAY NORTH OF POOLES ISLAND MD-
CHESAPEAKE BAY FROM POOLES ISLAND TO SANDY POINT MD-
CHESAPEAKE BAY FROM SANDY POINT TO NORTH BEACH MD-
CHESAPEAKE BAY FROM NORTH BEACH TO DRUM POINT MD-
CHESAPEAKE BAY FROM DRUM POINT MD TO SMITH POINT VA-
TIDAL POTOMAC FROM KEY BRIDGE TO INDIAN HEAD MD-
TIDAL POTOMAC FROM INDIAN HEAD TO COBB ISLAND MD-
TIDAL POTOMAC FROM COBB ISLAND MD TO SMITH POINT VA-
DISTRICT OF COLUMBIA-NORTHERN BALTIMORE-HARFORD-
SOUTHERN BALTIMORE-PRINCE GEORGES-ANNE ARUNDEL-CHARLES-ST. MARYS-
CALVERT-PRINCE WILLIAM/MANASSAS/MANASSAS PARK-FAIRFAX-
ARLINGTON/FALLS CHURCH/ALEXANDRIA-STAFFORD-SPOTSYLVANIA-
KING GEORGE-
329 PM EDT FRI JUN 26 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE MARYLAND PORTION OF THE
CHESAPEAKE BAY...TIDAL POTOMAC RIVER...AND ADJACENT COUNTIES IN
CENTRAL MARYLAND AND NORTHERN VIRGINIA AS WELL AS THE DISTRICT OF
COLUMBIA.

.DAY ONE...THIS AFTERNOON AND TONIGHT

SCATTERED SHOWERS AND THUNDERSTORMS WILL DEVELOP THIS AFTERNOON
AND EVENING AHEAD OF A COLD FRONT. SOME OF THESE STORMS MAY BECOME
SEVERE...PRODUCING DAMAGING WIND GUSTS AND MARGINALLY SEVERE HAIL.
A SEVERE THUNDERSTORM WATCH IS IN EFFECT FOR ALL AREAS EXCEPT
SOUTHERN MARYLAND AND ITS ADJACENT WATERS THROUGH 10 PM.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

A SMALL CRAFT ADVISORY MAY BE NEEDED SUNDAY AS A COLD FRONT MOVES
THROUGH THE WATERS.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS HAVE BEEN ACTIVATED THIS AFTERNOON AND EVENING.

MDZ003>005-009-010-501-502-VAZ021-025>031-036>042-050-051-
WVZ050>055-501>504-271000-
WASHINGTON-FREDERICK MD-CARROLL-MONTGOMERY-HOWARD-
EXTREME WESTERN ALLEGANY-CENTRAL AND EASTERN ALLEGANY-HIGHLAND-
AUGUSTA-ROCKINGHAM-SHENANDOAH-FREDERICK VA-PAGE-WARREN-CLARKE-
NELSON-ALBEMARLE-GREENE-MADISON-RAPPAHANNOCK-FAUQUIER-LOUDOUN-
ORANGE-CULPEPER-HAMPSHIRE-MORGAN-BERKELEY-JEFFERSON-PENDLETON-
HARDY-WESTERN GRANT-EASTERN GRANT-WESTERN MINERAL-EASTERN MINERAL-
329 PM EDT FRI JUN 26 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EASTERN WEST VIRGINIA...
NORTHERN AND CENTRAL VIRGINIA...AND CENTRAL AND WESTERN MARYLAND
WITH THE EXCEPTION OF GARRETT COUNTY.

.DAY ONE...THIS AFTERNOON AND TONIGHT

SCATTERED SHOWERS AND THUNDERSTORMS WILL DEVELOP THIS AFTERNOON
AND EVENING AHEAD OF A COLD FRONT. SOME OF THESE STORMS MAY
BECOME SEVERE...PRODUCING DAMAGING WIND GUSTS AND MARGINALLY
SEVERE HAIL. A SEVERE THUNDERSTORM WATCH IS IN EFFECT FOR
WESTERN AND CENTRAL MARYLAND...THE NORTHERN SHENANDOAH VALLEY AND
NORTHERN VIRGINIA THROUGH 10 PM.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOOTERS HAVE BEEN ACTIVATED THIS AFTERNOON AND EVENING.

BAJ/KRAMAR

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