Severe Thunderstorm Warning 147, NWS Baltimore/Washington

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
234 PM EDT TUE JUL 8 2014

.SYNOPSIS...
A COLD FRONT ACROSS THE GREAT LAKES AND MIDWEST WILL APPROACH THE
REGION LATE TODAY AND TONIGHT...CROSS THE AREA EARLY
WEDNESDAY...AND STALL OVER SOUTHERN VIRGINIA WEDNESDAY NIGHT
INTO THURSDAY. HIGH PRESSURE THEN BUILDS OVER THE MID-ATLANTIC
THURSDAY AND FRIDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
A SEVERE THUNDERSTORM WATCH IS IN EFFECT FOR PORTIONS OF WESTERN
MARYLAND AND EASTERN WEST VIRGINIA.

HIGH PRESSURE WILL REMAIN OVER THE ATLANTIC WHILE A COLD FRONT
MOVES INTO THE OHIO VALLEY LATE THIS AFTERNOON. THE COLD FRONT
WILL APPROACH THE NORTHWESTERN PORTION OF THE CWA TONIGHT. A
SOUTHWEST FLOW AHEAD OF THE COLD FRONT HAS USHERED IN MORE HOT AND
HUMID CONDITIONS. MAX TEMPS WILL RANGE FROM THE UPPER 70S AND
LOWER 80S ALONG THE RIDGES TO THE LOWER AND MIDDLE 90S ACROSS MOST
OTHER LOCATIONS.

THE HOT AND HUMID CONDITIONS HAS LEAD TO AN UNSTABLE
ATMOSPHERE...AND WITH DEWPOINTS A BIT HIGHER TODAY INSTABILITY
IS HIGHER THAN MONDAY. LATEST MESOANALYSIS ALONG WITH THE
MODIFIED 12Z KIAD RAOB SHOWS AROUND 1000 TO 1500 J/KG OF MLCAPE.

A FEW SHOWERS AND THUNDERSTORMS MAY DEVELOP ALONG A PRESSURE
TROUGH THIS AFTERNOON...BUT THE PRIMARY SOURCE OF CONVECTION IS
EXPECTED TO MOVE IN FROM WEST VIRGINIA LATER THIS AFTERNOON AND
EVENING. A LINE OF SHOWERS AND THUNDERSTORMS WILL MOVE INTO THE
POTOMAC HIGHLANDS BETWEEN 3 AND 5 PM THIS AFTERNOON AND IT WILL
REACH THE WASHINGTON AND BALTIMORE METROPOLITAN AREAS EARLY THIS
EVENING. GIVEN THE MODERATE AMOUNTS OF INSTABILITY AND FAVORABLE
SHEAR PROFILES...SEVERE THUNDERSTORMS ARE POSSIBLE. THE BEST
CHANCE FOR SEVERE THUNDERSTORMS WILL BE FROM NEAR AND WEST OF
INTERSTATE 95 THROUGH THE POTOMAC HIGHLANDS. THIS IS WHERE THE
HEIGHTS WILL BE LOWEST AND THE SHEAR PROFILES WILL BE STRONGEST.

THE CONVECTION TREND SHOULD DECREASE OVERNIGHT DUE TO THE LOSS OF
DAYTIME HEATING...BUT A SHOWER OR THUNDERSTORM CANNOT BE RULED OUT
WITH THE COLD FRONT NEARBY. WARM AND HUMID CONDITIONS WILL
PERSIST. MIN TEMPS WILL RANGE FROM THE 60S IN THE POTOMAC
HIGHLANDS AND SHENANDOAH VALLEY TO THE MIDDLE 70S IN WASHINGTON
AND BALTIMORE.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
THE COLD FRONT WILL MOVE INTO THE AREA WEDNESDAY FROM THE
NORTHWEST AND IT WILL SLOWLY PUSH SOUTH TOWARD SOUTHERN MARYLAND
AND CENTRAL VIRGINIA WEDNESDAY NIGHT. WARM AND HUMID CONDITIONS
ARE EXPECTED AHEAD OF THE FRONT WEDNESDAY...ESPECIALLY EAST OF THE
BLUE RIDGE MOUNTAINS. SOMEWHAT DRIER AND COOLER AIR MAY FILTER
INTO THE POTOMAC HIGHLANDS WEDNESDAY AFTERNOON. MAX TEMPS WILL
RANGE FROM THE 70S IN THE RIDGES OF THE ALLEGHENY AND POTOMAC
HIGHLANDS TO NEAR 90 IN WASHINGTON AND BALTIMORE AS WELL AS THE
VIRGINIA PIEDMONT.

THE WARM AND HUMID AIRMASS ALONG WITH FORCING FROM THE COLD FRONT
WILL ALLOW THE CHANCE OF SHOWERS AND THUNDERSTORMS...ESPECIALLY
DURING THE AFTERNOON AND EVENING HOURS. INSTABILITY WILL BE
LIMITED ACROSS THE NORTHWESTERN PORTION OF THE CWA...BUT FARTHER
SOUTH AND EAST HIGHER AMOUNTS OF INSTABILITY ALONG WITH STRONGER
SHEAR PROFILES AND MID-LEVEL DRY AIR SUGGESTS THAT A FEW
THUNDERSTORMS MAY BECOME SEVERE...WITH DAMAGING WIND AND HAIL
BEING THE PRIMARY THREATS. THE BEST CHANCE FOR STRONGER STORMS
WILL BE ACROSS CENTRAL VIRGINIA INTO SOUTHERN MARYLAND...WHERE
INSTABILITY WILL BE HIGHEST.

A NORTHERLY FLOW BEHIND THE FRONT WILL ALLOW FOR COOLER AND DRIER
CONDITIONS TO MOVE INTO MOST AREAS OVERNIGHT. MIN TEMPS WILL RANGE
FROM THE 50S IN THE ALLEGHENY HIGHLANDS TO THE LOWER AND MIDDLE
70S IN DOWNTOWN WASHINGTON AND BALTIMORE.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
SURFACE COLD FRONT ACROSS SOUTHEAST VIRGINIA THURSDAY MORNING
RETREATS SLIGHTLY NORTH THROUGH THE DAY. WITH SHORT WAVES MOVING
THROUGH CONFLUENT SOUTHWEST FLOW ALOFT...WILL SEE CONTINUED CHANCES
OF CONVECTION...MAINLY ELEVATED ALONG AND NORTH OF THE SURFACE FRONT
THURSDAY ALONG AND EAST OF I-95. WILL ALSO SEE CONVECTION POSSIBLE
WITH TERRAIN CIRCULATIONS THURSDAY AFTERNOON ACROSS POTOMAC
HIGHLANDS AND BLUE RIDGE. NAM KEEPS THE FRONT FARTHER NORTH IN
RESPONSE TO COASTAL LOW SYSTEM...BUT IS THE OUTLIER AT THIS TIME.
12Z GFS IS ALSO KEEPING HIGH PRESSURE FARTHER NORTH THAN PREVIOUS
RUNS HOWEVER...AND WITH UPPER TROUGH PUSHING OVERHEAD FRIDAY...WILL
BRING SOME SMALL CHANCE POPS INTO FORECAST. MAY NEED TO INCREASE
THESE POPS IF THESE TRENDS CONTINUE. WARM AIR ADVECTION PATTERN
ENSUES FOR THE WEEKEND INTO EARLY NEXT WEEK...ALTHOUGH STRONG
MOISTURE RETURN REMAINS LIMITED UNTIL MONDAY. INSTABILITY AND SHEAR
LOOK MORE FAVORABLE FOR ORGANIZED CONVECTION MONDAY/MONDAY NIGHT
AHEAD OF APPROACHING COLD FRONT ASSOCIATED WITH SOUTHWARD DIVING
CANADIAN CLOSED LOW.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
VFR CONDITIONS ARE EXPECTED MOST OF THE TIME THROUGH THIS EVENING.
SOUTHWEST WINDS WILL GUST AROUND 20 TO 25 KNOTS LATE THIS
AFTERNOON...BUT WINDS WILL DIMINISH AROUND SUNSET. SHOWERS AND
THUNDERSTORMS WILL LIKELY PASS THROUGH THE TERMINALS...FIRST
ACROSS THE WESTERN TERMINALS LATE THIS AFTERNOON AND THEN ACROSS
THE EASTERN TERMINALS THIS EVENING. BRIEF SUBVFR CONDITIONS ARE
EXPECTED IN THUNDERSTORMS...AND SOME THUNDERSTORMS WILL BE CAPABLE
OF PRODUCING GUSTY WINDS AND HAIL. VFR CONDITIONS ARE EXPECTED
MOST OF THE TIME LATE TONIGHT...BUT MVFR VSBYS FROM BR CANNOT BE
RULED OUT.

SOUTHWEST WINDS AROUND 10 KNOTS ARE EXPECTED WEDNESDAY ALONG WITH
VFR CONDITIONS. HOWEVER...A FEW SHOWERS AND THUNDERSTORMS CANNOT
BE RULED OUT DURING THE AFTERNOON AND EVENING. PATCHY FOG IS
POSSIBLE OVERNIGHT WEDNESDAY.

A STALLED FRONT WILL BRING CHANCES OF AFTERNOON STORMS
TO THE REGION THURSDAY INTO FRIDAY. WARMER AIR WILL RETURN FOR THE
WEEKEND INTO NEXT WEEK WITH INCREASING CHANCES OF THUNDERSTORMS.

&&

.MARINE...
THE GRADIENT WILL CONTINUE THIS THROUGH EARLY THIS EVENING. A
SMALL CRAFT ADVISORY IS IN EFFECT FOR THE WATERS DURING THIS
TIME. THE SMALL CRAFT ADVISORY CONTINUES THROUGH TONIGHT FOR THE
MARYLAND CHESAPEAKE BAY AND LOWER TIDAL POTOMAC RIVER. STRONG
GUSTY WINDS AND LARGE HAIL ARE POSSIBLE IN THUNDERSTORMS THIS
EVENING. SPECIAL MARINE WARNINGS WILL BE POSSIBLE. A COLD FRONT
WILL APPROACH THE WATERS WEDNESDAY. SHOWERS AND THUNDERSTORMS ARE
POSSIBLE MAINLY DURING THE AFTERNOON AND EVENING. A FEW
THUNDERSTORMS MAY CONTAIN GUSTY WINDS AND HAIL.

A STALLED FRONT WILL BRING CHANCES OF AFTERNOON STORMS TO
THE REGION THURSDAY INTO FRIDAY. WARMER AIR WILL RETURN FOR THE
WEEKEND INTO NEXT WEEK WITH INCREASING CHANCES OF THUNDERSTORMS.
SOUTHERLY WINDS WILL INCREASE THIS WEEKEND INTO NEXT WEEK AND SCA
CONDITIONS MAY BE MET.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT WEDNESDAY FOR ANZ530>534-
     537-539>541-543.
     SMALL CRAFT ADVISORY UNTIL 9 PM EDT THIS EVENING FOR ANZ535-
     536-538-542.

&&

SYNOPSIS...BJL
NEAR TERM...BJL
SHORT TERM...BJL
LONG TERM...AEB
AVIATION...BJL/AEB
MARINE...BJL/AEB

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