Special Weather Statement, NWS Baltimore/Washington

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
254 PM EDT WED SEP 28 2011

.SYNOPSIS...
A CUTOFF LOW PRESSURE SYSTEM WILL CONTINUE TO DRIFT EAST ACROSS THE
MIDWEST THROUGH TONIGHT. A COLD FRONT IS EXPECTED TO IMPACT THE
MID-ATLANTIC REGION ON THURSDAY. AN UPPER-LEVEL DISTURBANCE WILL
IMPACT THE REGION FRIDAY AND SATURDAY BEFORE CANADIAN HIGH PRESSURE
SLOWLY BUILDS OVERHEAD SUNDAY INTO EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THURSDAY EVENING/...
STALLED FRONTAL BOUNDARY REMAINS ACROSS THE BLUE RIDGE MOUNTAINS
THIS AFTERNOON. CONVECTION THAT MOVED THROUGH EARLIER THIS MORNING
HELPED STABILIZE THE ATMOS FOR MUCH OF THE MORNING AND EARLY
AFTERNOON. CLOUD HAVE BEGUN TO BREAK...AND HEATING HAS BEGUN
ACROSS MUCH OF THE CWFA.

WV LOOP AND 500MB ANALYSIS SHOWS A WEAK SHORTWAVE MOVING NORTH
ACROSS NORTHERN VIRGINIA AND EASTERN MARYLAND. DO EXPECT CONVECTION
TO FORM ALONG AND EAST OF THE FRONT ACROSS THE BLUE RIDGE THIS
AFTERNOON...AND BE AIDED BY THE WEAK SHORTWAVE ALOFT. A FEW STORMS
WILL HAVE THE POTENTIAL TO BECOME SEVERE...WITH THE PRIMARY THREAT
BEING DAMAGING WIND GUSTS. SOME LARGE HAIL IS ALSO POSSIBLE...WITH
AN ISOLATED TORNADO.

THE FRONT WILL BEGIN TO SHIFT EASTWARD LATE TONIGHT AS THE LONGWAVE
500MB TROUGH ALSO BEGINS TO SHIFT EAST. THE FRONT SHOULD MOVE OFF
THE COAST BY MIDDAY THURSDAY. STEEPENING MID LEVEL LAPSE RATES AND A
NEGATIVELY TILTED 500MB TROUGH MAY CONTRIBUTE TO SOME SCT SHRA/TSRA
DURING THE EARLY PART OF THURSDAY.

&&

.SHORT TERM /6 PM THURSDAY EVENING THROUGH FRIDAY/...
COOLER AND NOTICEABLY LESS HUMID CONDITIONS ARE EXPECTED BEHIND
THE COLD FRONT THURSDAY NIGHT THROUGH FRIDAY. MIN TEMPS THURSDAY
NIGHT WILL RANGE FROM THE 40S IN THE POTOMAC HIGHLANDS TO NEAR 60
IN WASHINGTON AND BALTIMORE. MAX TEMPS FRIDAY WILL RANGE FROM THE
50S IN THE MOUNTAINS TO THE UPPER 70S IN CENTRAL VIRGINIA.

A POTENT UPPER-LEVEL SHORTWAVE WILL DROP SOUTHWEST FROM CANADA INTO
THE GREAT LAKES THURSDAY NIGHT AND FRIDAY. THIS SYSTEM WILL CARVE
OUT AN UPPER-LEVEL TROUGH OVER THE MID-ATLANTIC DURING THIS TIME.
DESPITE THE COLDER AIR ALOFT...MOST PLACES WILL REMAIN DRY WITH JUST
SOME CLOUDS DUE TO A WESTERLY DOWNSLOPING FLOW BEHIND THE COLD
FRONT. THE ONE EXCEPTION WILL BE ACROSS THE ALLEGHENY AND POTOMAC
HIGHLANDS. AN UPSLOPE COMPONENT TO THE LOW-LEVEL FLOW MAY TRIGGER A
FEW SHOWERS...ESPECIALLY FRIDAY AFTERNOON WHERE THERE MAY BE LIMITED
INSTABILITY.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
ANOTHER SHORTWAVE WILL ROTATE AROUND THE TROUGH CAUSING AN
UPPER-LEVEL LOW TO CLOSE OFF FRIDAY NIGHT INTO SATURDAY. A NORTHWEST
FLOW WILL AROUND THIS SYSTEM WILL USHER IN MORE MOISTURE FROM THE
GREAT LAKES. DEEPER MOISTURE ALONG WITH INCREASED LIFT FROM THE
UPPER-LEVEL LOW WILL CAUSE PLENTY OF CLOUDS ALONG WITH THE
POSSIBILITY OF SHOWERS. THE BEST CHANCE FOR SHOWERS WILL BE ACROSS
THE ALLEGHENY AND POTOMAC HIGHLANDS DUE TO AN UPSLOPE COMPONENT TO
THE LOW-LEVEL FLOW.

COLDER AIR ALOFT ALONG WITH INCREASED CLOUD COVER AND MOISTURE WILL
COMBINE WITH A NORTHWEST FLOW TO USHER IN THE COOLEST AIRMASS OF THE
SEASON. MIN TEMPS FRIDAY NIGHT WILL RANGE FROM THE 30S IN THE
MOUNTAINS TO THE LOWER 50S IN WASHINGTON AND BALTIMORE. MAX TEMPS
SATURDAY WILL REMAIN IN THE 30S ACROSS THE RIDGE TOPS OF THE
ALLEGHENY AND POTOMAC HIGHLANDS TO NEAR 60 IN WASHINGTON AND
BALTIMORE. STRONG COLD ADVECTION AND LIFT MAY CAUSE ENOUGH COLD AIR
ALOFT FOR A FEW SNOW SHOWERS TO MIX IN ACROSS THE RIDGE TOPS OF THE
ALLEGHENY AND POTOMAC HIGHLANDS OVERNIGHT FRIDAY...GENERALLY FOR
ELEVATIONS ABOVE 3KFT. NO ACCUMULATION IS EXPECTED.

AN UPPER-LEVEL TROUGH WILL REMAIN OVERHEAD SATURDAY NIGHT CAUSING
MORE UNSETTLED AND COOL CONDITIONS. THE MID-LEVEL TROUGH WILL SLOWLY
MOVE EAST SUNDAY AND HIGH PRESSURE IS EXPECTED TO BUILD OVERHEAD
LATER SUNDAY THROUGH THE MIDDLE PORTION OF NEXT WEEK. DRY CONDITIONS
ARE EXPECTED DURING THIS TIME ALONG WITH A MODERATING TREND IN
TEMPERATURES.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
SCT/NMRS SHRA/TSRA EXPECTED AT THE EASTERN TERMINAL SITES THIS
AFTERNOON AND OVERNIGHT. ACTIVITY WILL FORM ALONG AND AHEAD OF A
STALLED FRONTAL BOUNDARY LATE THIS AFTERNOON. CONVECTION WILL SLOWLY
PUSH EASTWARD OVERNIGHT...WITH LINGERING SHRA/TSRA FOR THE EARLY
HALF OF THURSDAY.

VFR CONDITIONS ARE EXPECTED THURSDAY NIGHT THROUGH FRIDAY. WESTERLY
WINDS MAY GUST AROUND 20 KNOTS...ESPECIALLY FRIDAY AFTERNOON. AN
UPPER-LEVEL TROUGH WILL BRING UNSETTLED CONDITIONS FRIDAY NIGHT
THROUGH SATURDAY. SCATTERED SHOWERS ALONG WITH MVFR CIGS/VSBYS ARE
POSSIBLE. NORTHWEST WINDS WILL GUST AROUND 20 KNOTS.

HIGH PRESSURE WILL SLOWLY BUILD OVER THE TERMINALS SUNDAY THROUGH
EARLY NEXT WEEK.

&&

.MARINE...
S/SW WINDS AOB 15 KT THROUGH THURSDAY. STRONG/SEVERE CONVECTION MAY
LEAD TO SMW THROUGH THE OVERNIGHT HOURS. A WEAK FRONT WILL CROSS THE
WATERS TOMORROW.

WESTERLY WINDS ARE EXPECTED BEHIND A COLD FRONT THURSDAY NIGHT
THROUGH FRIDAY. AN SCA MAY BE NEEDED FOR PORTIONS OF THE WATERS
FRIDAY.

AN UPPER-LEVEL TROUGH WILL BUILD OVER THE WATERS FRIDAY NIGHT
THROUGH SATURDAY. AN SCA WILL LIKELY BE NEEDED FOR PORTIONS OF THE
WATERS. HIGH PRESSURE WILL SLOWLY BUILD OVERHEAD SUNDAY INTO EARLY
NEXT WEEK. A SMALL CRAFT ADVISORY CONDITIONS ARE LIKELY DURING THIS
TIME.

&&

.TIDES/COASTAL FLOODING...
TIDAL ANOMALIES ARE RUNNING AROUND A FOOT ABOVE NORMAL THIS
AFTERNOON. WILL LEAVE THE CFW HEADLINE AS IS. POSITIVE ANOMALIES
WILL CONTINUE UNTIL A W/NW WIND OCCURS.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...COASTAL FLOOD ADVISORY UNTIL 11 PM EDT THIS EVENING FOR DCZ001.
MD...COASTAL FLOOD ADVISORY UNTIL 1 AM EDT THURSDAY FOR MDZ007-011-
     014-017-018.
     COASTAL FLOOD ADVISORY UNTIL 11 PM EDT THIS EVENING FOR MDZ013-
     016.
VA...COASTAL FLOOD ADVISORY UNTIL 11 PM EDT THIS EVENING FOR
     VAZ052>055-057.
WV...NONE.
MARINE...NONE.

&&

LISTEMAA/LASORSA

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
244 PM EDT WED SEP 28 2011

ANZ530>543-DCZ001-MDZ006-007-011-013-014-016>018-VAZ052>057-
291000-
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-
PATAPSCO RIVER INCLUDING BALTIMORE HARBOR-
CHESTER RIVER TO QUEENSTOWN MD-EASTERN BAY-
CHOPTANK RIVER TO CAMBRIDGE MD AND THE LITTLE CHOPTANK RIVER-
PATUXENT RIVER TO BROOMES ISLAND MD-
TANGIER SOUND AND THE INLAND WATERS SURROUNDING BLOODSWORTH
ISLAND-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-
244 PM EDT WED SEP 28 2011

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 THUNDERSTORMS ARE EXPECTED TO DEVELOP LATE THIS
AFTERNOON AND EVENING ACROSS THE OUTLOOK AREA. A FEW STORMS COULD
BECOME SEVERE WITH THE POTENTIAL TO PRODUCE DAMAGING WIND
GUSTS...LARGE HAIL AND AN ISOLATED TORNADO.

A COASTAL FLOOD ADVISORY IS IN EFFECT THROUGH LATE TONIGHT FOR THE
ALONG THE TIDAL POTOMAC AND WESTERN SHORE OF THE CHESAPEAKE BAY. REFER
TO THE LATEST HAZARD MESSAGE /CFWLWX/ FOR DETAILS.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

MINOR COASTAL FLOODING IS EXPECTED AGAIN ON THURSDAY AROUND HIGH
TIDE.

A SMALL CRAFT ADVISORY LIKELY WILL BE NEEDED FRIDAY THROUGH MONDAY
FOR PORTIONS OF THE WATERS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON AND
EVENING.

MDZ003>005-009-010-501-502-VAZ025>031-036>040-042-050-051-501>504-
WVZ050>053-055-501>506-291000-
WASHINGTON-FREDERICK MD-CARROLL-MONTGOMERY-HOWARD-
EXTREME WESTERN ALLEGANY-CENTRAL AND EASTERN ALLEGANY-AUGUSTA-
ROCKINGHAM-SHENANDOAH-FREDERICK VA-PAGE-WARREN-CLARKE-NELSON-
ALBEMARLE-GREENE-MADISON-RAPPAHANNOCK-LOUDOUN-ORANGE-CULPEPER-
NORTHERN FAUQUIER-SOUTHERN FAUQUIER-WESTERN HIGHLAND-
EASTERN HIGHLAND-HAMPSHIRE-MORGAN-BERKELEY-JEFFERSON-HARDY-
WESTERN GRANT-EASTERN GRANT-WESTERN MINERAL-EASTERN MINERAL-
WESTERN PENDLETON-EASTERN PENDLETON-
244 PM EDT WED SEP 28 2011

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 THUNDERSTORMS ARE EXPECTED TO DEVELOP LATE THIS
AFTERNOON AND EVENING PRIMARILY ALONG AND EAST OF THE BLUE RIDGE
MOUNTAINS. A FEW STORMS COULD BECOME SEVERE AND WILL HAVE THE
POTENTIAL TO PRODUCE DAMAGING WIND GUSTS AND AN ISOLATED TORNADO.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THE COMBINATION OF LIGHT WINDS...DRY AIR AND MINIMUM TEMPERATURES
IN THE LOW TO MID 30S COULD LEAD TO FROST FORMATION OVERNIGHT
SUNDAY IN THE POTOMAC HIGHLANDS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON AND
EVENING.

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
621 PM EDT WED SEP 28 2011

VAZ051-052-055-056-502-282245-
STAFFORD VA-CULPEPER VA-PRINCE WILLIAM/MANASSAS/MANASSAS PARK VA-
SOUTHERN FAUQUIER VA-SPOTSYLVANIA VA-
621 PM EDT WED SEP 28 2011

...STRONG THUNDERSTORM TO AFFECT STAFFORD...CULPEPER...PRINCE
WILLIAM...SOUTHERN FAUQUIER AND SPOTSYLVANIA COUNTIES...

AT 619 PM EDT...DOPPLER RADAR INDICATED A STRONG THUNDERSTORM OVER
GOLDVEIN...MOVING NORTHEAST AT 25 MPH.

LOCATIONS IMPACTED INCLUDE HEFLIN...SOMERVILLE...ROSEVILLE...RUBY...
SHILOH AND GARRISONVILLE.

THIS STORM IS PRODUCING FREQUENT CLOUD TO GROUND LIGHTNING. MOVE
INDOORS IMMEDIATELY FOR YOUR SAFETY. IF YOU CAN HEAR THUNDER...YOU
ARE CLOSE ENOUGH TO BE STRUCK BY LIGHTNING.

HEAVY DOWNPOURS...WIND GUSTS OF 40 TO 50 MPH AND SMALL HAIL CAN ALSO
BE EXPECTED WITH THIS STORM. THE HEAVY RAIN MAY REDUCE VISIBILITIES
TO BELOW ONE MILE AND CAUSE PONDING OF WATER ON ROADWAYS.

&&

LAT...LON 3870 7749 3853 7730 3833 7767 3845 7775
TIME...MOT...LOC 2219Z 227DEG 21KT 3844 7763

JRK