Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 081834 AFDLWX 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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