Severe Thunderstorm Warning 321, NWS Baltimore/Washington

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1144 AM EDT SUN JUL 27 2008

.SYNOPSIS...
A COLD FRONT WILL APPROACH THE AREA TODAY...MOVING THROUGH
TONIGHT AND STALLING ACROSS SOUTHEAST VIRGINIA MONDAY. DRY WEATHER CAN
BE EXPECTED MONDAY...BUT THE FRONT WILL ADVANCE NORTH DURING THE
MIDDLE OF THE WEEK INCREASING HUMIDITY AND THE CHANCES FOR
THUNDERSTORMS.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

UPDATE FOR SEVERE THUNDERSTORM WATCH 759 IN EFFECT UNTIL 8 PM FOR
LWX COUNTIES EAST OF THE BLUE RIDGE.

TODAY LOOKS LIKE A VERY ACTIVE WEATHER DAY. SURFACE ANALYSIS AT
14Z SHOWS A TROUGH ALONG THE BLUE RIDGE AND A COLD FRONT NEARING
THE APPALACHIANS. VISIBLE SATELLITE IMAGERY AND SURFACE
OBSERVATIONS SHOW PLENTY OF CLEARING ACROSS THE REGION...WITH
DEBRIS CLOUDS FROM OVERNIGHT CONVECTION EXITING THE EASTERN
FORECAST AREA.

THE MODIFIED 12Z KIAD RAOB HAS OVER 2000 J/KG CAPE...WITH MODELS
PRODUCING AROUND 2500 J/KG. THERE IS ALSO AROUND 30 KNOTS OF
SHEAR. LAPSE RATES WILL STEEPEN THIS AFTERNOON WITH A COOL UPPER
TROUGH NEARBY AND WARMING LOW LEVELS. OVERALL...LOOKS LIKE PLENTY
OF INSTABILITY TO WORK WITH. THERE IS NO LACK OF LIFTING TRIGGERS
TODAY...WITH THE LEE TROUGH...COLD FRONT...PROBABLY BAY
BREEZE...AND UPPER TROUGH. PRIMARY THREATS TODAY ARE DAMAGING
WINDS AND LARGE HAIL. LOCAL WRF-ARW INDICATES INITIATION BY
NOON...WHICH IS SUPPORTED BY THE ISOLATED CELLS DEVELOPING IN THE
POTOMAC HIGHLANDS. WITH EXISTING SHEAR...THESE STORMS ARE EXPECTED
TO BECOME BETTER ORGANIZED THROUGH THE DAY.

A SECOND ROUND OF STORMS IS EXPECTED ALONG THE FRONT LATER THIS
AFTERNOON. WHILE THE AIRMASS WILL BE SOMEWHAT WORKED OVER BY
MORNING AND EARLY AFTERNOON ACTIVITY...ENOUGH EXISTING INSTABILITY
AND MESOSCALE EFFECTS TO SUPPORT MORE STRONG TO SEVERE STORMS.
THIS ROUND WOULD MOST LIKELY HAVE MORE ORGANIZED LINE SEGMENTS.

WILL BE DOING A SPECIAL RAOB THIS AFTERNOON FOR WEATHER SUPPORT.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
A SECOND ROUND OF STORMS ASSOCIATED WITH THE COLD FRONT WILL BE
MOVING EAST OF THE AREA THROUGH THE EVENING HOURS BECOMING MORE
NORTH AND WEST.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
NORTHERN HEMISPHERIC 500MB HEIGHT/ANOMALY PATTERN DURING THE PAST 5
DAYS INDICATES AN UPPER LOW MOVING SOUTH ALONG THE WESTERN CANADIAN
BORDER. THIS IS INFLUENCING RIDGING OVER THE NORTHERN
ROCKIES...FORMING TROUGHING OVER THE HUDSON BAY REGION AND RIDGING
TO STRENGTHEN OVER THE CANADIAN MARITIMES. RIDGING DOMINATES THE
CENTRAL CONUS. WATER VAPOR LOOP SHOWS A SHORTWAVE LIFTING INTO NEW
ENGLAND...AS THE NEXT WAVE DROPS SOUTHEAST OVER THE OHIO VALLEY. A
STRONGER TRAILING WAVE IS DROPPING OVER THE GREAT LAKES. 02Z SURFACE
MAP PLACED A TROUGH IN THE LEE OF THE CENTRAL APPALACHIANS. A COLD
FRONT WAS APPROACHING FROM THE OHIO VALLEY. 1015MB HIGH PRESSURE
DOMINATED THE MIDWEST.

HIGH PRESSURE AND DECREASING MOISTURE EXPECTED FOR THE EARLY WORK
WEEK...BEFORE MOISTURE AND BUILDING HEAT RETURN MID WEEK. WHILE
MEDIUM RANGE MODELS ARE IN DECENT AGREEMENT OF MAINTAINING THE
TROUGH FEATURE ALOFT THROUGH THE LONG RANGE...CONVECTIVE PROCESSES
WILL LIKELY DICTATE TIMING OF NORTHWARD MOVEMENT OF THE FRONTAL
BOUNDARY. WITH THE GFS EXHIBITING CONVECTIVE FEEDBACK...SIDED CLOSER
TO THE EUROPEAN DEPICTION AT THIS TIME.

&&

.AVIATION /16Z SUNDAY THROUGH THURSDAY/...
SOUTHERLY TO SOUTHWESTERLY WINDS TODAY AT ALL TERMINALS WITH A
TROUGH OVER THE FORECAST AREA. MARINE FRONT TO PRODUCE SELY WINDS
KDCA/KBWI/KMTN BY THIS AFTN... WHICH WILL ENHANCE CNVGNC ERN HALF
OF AREA TDA. TSTMS SHUD DVLP BY LATE MRNG OR EARLY AFTN.
ATTM...WILL INCLUDE CB RKRAMARS ALL SITES EARLY AFTN THRU MID
EVE...AND WILL REFINE TIMING OF TSTM IMPACT IN 12Z ISSUANCE.

HIGH PRESSURE BUILDS INTO THE REGION FOR THE EARLY WORK WEEK.
PROBABILITY FOR THUNDERSTORMS ONCE AGAIN INCREASES MID WEEK AS
HUMIDITY RETURNS NORTHWARD INTO THE MID ATLANTIC.

&&

.MARINE...
AS SFC TROF SHARPENS ACRS CNTRL ZONES TDA...SLY WINDS SHUD INCR IN
CHSPK BAY...SPCLY SRN PORTION. WILL INCLUDE SMALL CRAFT ADZY 27/16Z
THRU 28/00Z FOR CHSPK BAY FROM SMITH POINT TO SANDY POINT...AND FOR
POTOMAC FROM COBB ISLAND TO SMITH POINT. ADZY CONDITIONS SHUD
SUBSIDE THIS EVE AS DIFFUSE CDFNT MOVES ACRS.

HIGH PRESSURE BUILDS INTO THE REGION FOR THE EARLY WORK WEEK.
PROBABILITY FOR THUNDERSTORMS ONCE AGAIN INCREASES MID WEEK AS
HUMIDITY RETURNS NORTHWARD INTO THE MID ATLANTIC.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 10 PM EDT THIS EVENING FOR
     ANZ532>534-537.

&&

SYNOPSIS...SJR
NEAR TERM...SAR
SHORT TERM...MRK
LONG TERM...SJR
AVIATION...MRK/SJR
MARINE...MRK/SJR

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1147 AM EDT SUN JUL 27 2008

ANZ530>537-DCZ001-MDZ006-007-011-013-014-016>018-VAZ052>057-
281000-
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-
1147 AM EDT SUN JUL 27 2008

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

A SEVERE THUNDERSTORM WATCH IS IN EFFECT UNTIL 8 PM. SCATTERED TO
NUMEROUS THUNDERSTORMS ARE EXPECTED TO DEVELOP ACROSS THE AREA BY
LATE THIS MORNING AS A STRONG UPPER DISTURBANCE MOVES ACROSS AND A
COLD FRONT APPROACHES. SOME STORMS MAY BECOME SEVERE...AND WILL BE
CAPABLE OF PRODUCING DAMAGING WIND GUSTS AND LARGE HAIL.

A SMALL CRAFT ADVISORY IS IN EFFECT FROM NOON TO 10 PM FOR THE
LOWER TIDAL POTOMAC AND THE CHESAPEAKE BAY FROM SMITH POINT TO
SANDY POINT.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

MOISTURE AND RETURNING WARMTH WILL CONTRIBUTE TO HEAT INDICES
NEAR 100 DEGREES MID WEEK.

.SPOTTER INFORMATION STATEMENT...

SKYWARN HAS BEEN ACTIVATED FOR LOCATIONS EAST OF THE BLUE RIDGE.
PLEASE CONTACT THE NATIONAL WEATHER SERVICE WITH SEVERE WEATHER
REPORTS.

MDZ003>005-009-010-501-502-VAZ021-025>031-036>042-050-051-
WVZ050>055-501>504-281000-
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-
1147 AM EDT SUN JUL 27 2008

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

A SEVERE THUNDERSTORM WATCH IS IN EFFECT FOR LOCATIONS EAST OF THE
BLUE RIDGE UNTIL 8 PM. SCATTERED TO NUMEROUS THUNDERSTORMS ARE
EXPECTED TO DEVELOP ACROSS THE AREA BY LATE THIS MORNING AS A
STRONG UPPER DISTURBANCE MOVES ACROSS AND A COLD FRONT APPROACHES.
SOME STORMS MAY BECOME SEVERE...AND WILL BE CAPABLE OF PRODUCING
DAMAGING WIND GUSTS AND LARGE HAIL.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

MOISTURE AND RETURNING WARMTH WILL CONTRIBUTE TO HEAT INDICES
NEAR 100 DEGREES MID WEEK.

.SPOTTER INFORMATION STATEMENT...

SKYWARN HAS BEEN ACTIVATED FOR LOCATIONS EAST OF THE BLUE RIDGE.
PLEASE CONTACT THE NATIONAL WEATHER SERVICE WITH SEVERE WEATHER
REPORTS.

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1251 PM EDT SUN JUL 27 2008

MDZ009-VAZ030-031-041-042-052-053-271715-
CLARKE VA-FAIRFAX VA-FAUQUIER VA-LOUDOUN VA-MONTGOMERY MD-
PRINCE WILLIAM/MANASSAS/MANASSAS PARK VA-WARREN VA-
1251 PM EDT SUN JUL 27 2008

...STRONG THUNDERSTORMS TO AFFECT MONTGOMERY...FAUQUIER...WARREN...
CLARKE...LOUDOUN...PRINCE WILLIAM/MANASSAS/MANASSAS PARK AND FAIRFAX
COUNTIES...

AT 1251 PM EDT...DOPPLER RADAR INDICATED STRONG THUNDERSTORMS ALONG A
LINE EXTENDING FROM HUGHESVILLE TO 2 MILES SOUTH OF BLUE MOUNTAIN...
MOVING EAST AT 34 MPH.

THESE STORMS WILL BE CAPABLE OF PRODUCING SMALL HAIL AND WIND GUSTS
TO 50 MPH.

THE COMMUNITIES OF DELAPLANE...ASHBURN...COUNTRYSIDE...ARCOLA AND
NORTH POTOMAC WILL BE AFFECTED BY THESE STORMS.

RESIDENTS IN THESE AREAS SHOULD REMAIN ALERT IN CASE WARNINGS ARE
ISSUED.

HTS

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