Severe Thunderstorm Warning 138, NWS Baltimore/Washington

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
245 PM EDT TUE JUL 3 2012

.SYNOPSIS...
A FRONTAL BOUNDARY ACROSS CENTRAL VIRGINIA WILL SLOWLY MOVE
NORTHWARD THROUGH THE AREA. AN UPPER LEVEL DISTURBANCE WILL TRACK
NORTH OF THE AREA WEDNESDAY. HIGH PRESSURE WILL RETURN FOR THE
LATTER PART OF THE WEEK.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
WARM FRONT WAS LIFTING NORTH TOWARD THE MASON DIXON LINE THIS
AFTERNOON. DEWPOINTS ARE STILL RELATIVELY LOW ACROSS THE CWA...BUT
AS LOW LEVEL WINDS SHIFT TO THE SOUTH EXPECT DEWPOINTS AND
PRECIPITABLE WATER VALUES TO CREEP UP THROUGH THE EVENING.

GIVEN INITIAL DRY AIR AND SOME WARMING GOING ON ALOFT...EXPECT
CONVECTION TO HOLD OFF THROUGH AT LEAST MID-AFTERNOON. AT
17Z...ISOLATED STORMS WERE BEGINNING TO DEVELOP OVER THE SOUTHERN
APPALACHIANS...AND A COMPLEX OF THUNDERSTORMS THAT WAS OVER
NORTHEAST OHIO THIS MORNING WAS MOVING INTO NORTHWEST PENNSYLVANIA.

LATER THIS AFTERNOON...SIMILAR TO WHAT IS OCCURRING ACROSS THE
SOUTHERN APPALACHIANS...ISOLATED STORMS MAY POP UP OVER THE HIGHER
TERRAIN. HOWEVER...EXPECT MUCH OF THE REST OF THE CWA TO REMAIN
DRY WITH PARTLY SUNNY SKIES DUE TO CIRRUS FROM MCS DEBRIS.

IF THAT MCS HOLDS TOGETHER...THEN IT LIKELY WILL BRING AT LEAST
SCATTERED THUNDERSTORMS ACROSS THE CWA THIS EVENING. EVEN IF IT
WEAKENS...ADDITIONAL STORMS MAY RE-FIRE ALONG ITS BOUNDARY AS
MOISTURE INCREASES THIS EVENING. THIS IS DEPICTED BY THE HRRR. THERE
OBVIOUSLY REMAINS SOME UNCERTAINTY WITH THE EVOLUTION OF THIS
PARTICULAR SYSTEM...SO HAVE KEPT POPS IN THE CHANCE CATEGORY THIS
EVENING.

IN ADDITION...SOME MODEL GUIDANCE INCLUDING THE NAM...GFS AND LWX
WRF-ARW INDICATES THAT A CLUSTER OF THUNDERSTORMS...POSSIBLY AN
MCS...MAY APPROACH OR MOVE INTO THE CWA OVERNIGHT. THIS MAY BE
SOMEWHAT AFFECTED BY WHAT OCCURS EARLIER THIS EVENING...AND THUS
THERE ARE INHERENT UNCERTAINTIES. WILL CONTINUE CHANCE POPS
OVERNIGHT.

ON WEDNESDAY...ATMOSPHERE WILL BE MOIST AND UNSTABLE. CAN/T RULE OUT
SOME ONGOING CONVECTION AT THE START OF THE DAY...BUT MOST GUIDANCE
SUGGEST THE CWA WOULD BE DRY DURING THE LATE MORNING/EARLY AFTERNOON
BEFORE SCATTERED THUNDERSTORMS DEVELOP. LEE TROUGH AND MID-LEVEL
SHORTWAVE APPEAR TO BE SUFFICIENT TRIGGERS. SOME OF THE STORMS MAY
BE SEVERE WITH LARGE HAIL AND DAMAGING WIND GUSTS.

CLOUDS WILL HAVE AN IMPACT ON HOW WARM IT GETS ON WEDNESDAY. CURRENT
FORECAST IS FOR MID 90S...AND WITH HIGHER HUMIDITY THAN TODAY IT
WILL FEEL EVEN HOTTER. EAST OF THE BLUE RIDGE...HEAT INDEX VALUES
ARE FORECAST TO BE AROUND 100 DEGREES.

&&

.SHORT TERM /WEDNESDAY NIGHT/...
AN UPPER-LEVEL DISTURBANCE WILL PASS THROUGH IN THE NORTHWEST FLOW
ALOFT. WARM AND HUMID CONDITIONS WILL PERSIST DURING THIS TIME. HIGH
AMOUNTS OF INSTABILITY ALONG WITH FORCING FROM THE UPPER-LEVEL
DISTURBANCE WILL CAUSE A CHANCE FOR SHOWERS AND
THUNDERSTORMS...MAINLY DURING THE EVENING. ANY T-STORMS THAT DO
DEVELOP WILL HAVE THE POTENTIAL TO PRODUCE DAMAGING WIND GUSTS DUE
TO HIGH AMOUNTS OF INSTABILITY. THE HEAT AND HUMIDITY WILL ALSO BE A
THREAT FOR PEOPLE VENTURING OUTDOORS WEDNESDAY EVENING. HEAT INDICES
WILL BE IN THE 80S AND 90S ACROSS MOST AREAS DURING THIS TIME.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
UPPER-LEVEL HIGH PRESSURE OVER THE MIDWEST WILL EXTEND EAST TOWARD
THE MID-ATLANTIC THURSDAY AND FRIDAY. SUBSIDENCE ASSOCIATED WITH
THIS SYSTEM WILL PRODUCE UNUSUALLY HOT CONDITIONS. HUMIDITY WILL
ALSO REMAIN HIGH AS THE LOW-LEVEL FLOW CONTINUES TO CIRCULATE AROUND
HIGH PRESSURE THAT EXTENDS FROM THE ATLANTIC OCEAN INTO THE SOUTHERN
CONUS. HEAT INDICES NEAR OR ABOVE 100 DEGREES ARE EXPECTED ACROSS
MANY LOCATIONS THURSDAY AND FRIDAY. A HEAT ADVISORY MAY BE NEEDED
FOR PORTIONS OF THE AREA DURING THIS TIME. MOST LOCATIONS WILL
REMAIN DRY SINCE SUBSIDENCE FROM THE UPPER-LEVEL HIGH WILL PROVIDE A
STRONG CAPPING INVERSION. THE ONE EXCEPTION MAY BE ACROSS THE
CENTRAL SHENANDOAH VALLEY INTO THE POTOMAC HIGHLANDS THURSDAY
AFTERNOON WHERE AN ISOLATED T-STORM CANNOT BE RULED OUT.

THE UPPER-LEVEL RIDGE WILL FLATTEN OUT A BIT SATURDAY AS SHORTWAVE
ENERGY PASSES BY TO THE NORTH. THIS WILL ALLOW FOR A BOUNDARY TO
APPROACH THE AREA SATURDAY NIGHT INTO SUNDAY. HOT AND HUMID
CONDITIONS WILL PERSIST THROUGH THE WEEKEND...BUT THE BOUNDARY WILL
BRING AN INCREASING CHANCE FOR SHOWERS AND T-STORMS. THE BOUNDARY
MAY STALL OUT NEAR THE REGION DURING THE EARLY PORTION OF NEXT
WEEK...CAUSING UNSETTLED CONDITIONS.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
MAIN CHALLENGE REVOLVES AROUND THUNDERSTORM POTENTIAL THROUGH
WEDNESDAY. THERE REMAINS UNCERTAINTY REGARDING EVOLUTION OF
THUNDERSTORM CLUSTERS AND ASSOCIATED TIMING. FOLLOWING RECENT HRRR
RUNS...HAVE INSERTED VCTS/CB ACROSS MOST TAF SITES THIS EVENING AS
UPSTREAM MCS MOVES SOUTHEAST WITH TIME...POSSIBLY BUILDING
SOUTHWARD. SOME GUIDANCE REVEALS THAT ADDITIONAL THUNDERSTORMS MAY
BE POSSIBLE LATE TONIGHT...BUT LOW CONFIDENCE PRECLUDED INCLUSION IN
18Z TAFS. LEE TROUGH AND MID-LEVEL SHORTWAVE WILL BRING A CHANCE OF
THUNDERSTORMS BY WEDNESDAY AFTERNOON.

VFR CONDITIONS ARE EXPECTED MOST OF THE TIME WEDNESDAY NIGHT THROUGH
SUNDAY. SCATTERED T-STORMS ARE POSSIBLE WEDNESDAY EVENING AND
T-STORMS WILL BE CAPABLE OF PRODUCING GUSTY WINDS AND HAIL.

DRY CONDITIONS ARE EXPECTED THURSDAY AND FRIDAY ACROSS MOST OF THE
TERMINALS. AN APPROACHING BOUNDARY WILL BRING INCREASING CHANCES FOR
SHOWERS AND THUNDERSTORMS DURING THE WEEKEND.

&&

.MARINE...
REST OF THE AFTERNOON SHOULD BE DRY ACROSS THE WATERS...BUT WILL
HAVE TO WATCH FOR THE POTENTIAL OF SCATTERED THUNDERSTORMS THIS
EVENING WHICH COULD PRODUCE GUSTY WINDS. A CHANCE OF THUNDERSTORMS
WILL CONTINUE INTO WEDNESDAY...PARTICULARLY IN THE AFTERNOON AND
EVENING.

WINDS ARE EXPECTED TO REMAIN BELOW SCA CRITERIA FOR MOST OF THE
EXTENDED PERIOD. SCATTERED T-STORMS WEDNESDAY EVENING WILL BE
CAPABLE OF PRODUCING GUSTY WINDS AND HAIL.

A BOUNDARY WILL APPROACH THE WATERS DURING THE WEEKEND...BRINGING AN
INCREASING CHANCE FOR SHOWERS AND T-STORMS.

&&

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

&&

PRODUCTS...PELOQUIN/LASORSA

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
252 PM EDT TUE JUL 3 2012

ANZ530>543-DCZ001-MDZ006-007-011-013-014-016>018-VAZ052>057-
041000-
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-
252 PM EDT TUE JUL 3 2012

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 MAY AFFECT THE AREA THIS EVENING. A FEW
THUNDERSTORMS MAY BE STRONG TO SEVERE WITH LARGE HAIL AND DAMAGING
WIND GUSTS.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

THUNDERSTORMS ARE POSSIBLE WEDNESDAY /THE FOURTH OF JULY/ AS A
AN UPPER LEVEL DISTURBANCE APPROACHES THE AREA. SOME OF THE STORMS MAY
BE SEVERE...ESPECIALLY IN THE AFTERNOON AND EVENING.

THE COMBINATION OF HEAT AND HUMIDITY WILL PROMOTE HEAT INDICES IN
EXCESS OF 100 DEGREES ON WEDNESDAY.

HEAT INDICES OVER 100 ARE POSSIBLE THURSDAY THROUGH SATURDAY. HEAT
ADVISORIES MAY BE NEEDED DURING THIS TIME.

.SPOTTER INFORMATION STATEMENT...

LIMITED SPOTTER ACTIVATION MAY BECOME NECESSARY THIS EVENING.
SPOTTER ACTIVATION MAY ALSO BE REQUIRED ON WEDNESDAY.

MDZ003>005-009-010-501-502-VAZ025>031-036>040-042-050-051-501>504-
WVZ050>053-055-501>506-041000-
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-
252 PM EDT TUE JUL 3 2012

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 WILL AFFECT THE AREA THROUGH THIS EVENING. A
FEW THUNDERSTORMS MAY BE STRONG TO SEVERE WITH LARGE HAIL AND
DAMAGING WIND GUSTS.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

THUNDERSTORMS ARE ALSO EXPECTED WEDNESDAY /THE FOURTH OF JULY/.
SOME OF THE STORMS MAY BE SEVERE...ESPECIALLY IN THE AFTERNOON AND
EVENING.

HEAT INDICES WILL APPROACH 100 DEGREES EAST OF THE BLUE RIDGE
MOUNTAINS WEDNESDAY.

HEAT INDICES OVER 100 DEGREES ARE POSSIBLE THURSDAY THROUGH
SATURDAY. HEAT ADVISORIES MAY BE NEEDED DURING THIS TIME.

.SPOTTER INFORMATION STATEMENT...

LIMITED SPOTTER ACTIVATION MAY BECOME NECESSARY LATE THIS
AFTERNOON OR EVENING. SPOTTER ACTIVATION MAY ALSO BE REQUIRED ON
WEDNESDAY.

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