Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 211438 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1038 AM EDT SUN SEP 21 2014 .SYNOPSIS... LOW PRESSURE WILL TRACK NORTHEAST OFF THE MID- ATLANTIC COAST INTO THIS EVENING. A COLD FRONT WILL CROSS THE REGION LATE THIS AFTERNOON THROUGH THIS EVENING...FOLLOWED BY A RETURN OF HIGH PRESSURE MONDAY THROUGH LATE IN THE WEEK. && .NEAR TERM /THROUGH TONIGHT/... COASTAL LOW PRESSURE CONTINUES TO MOVE OFFSHORE...WITH EFFECTS GENERALLY EAST OF OUR AREA. LOW CLOUDS OVER BALTIMORE HAVE BEEN SLOW TO MOVE OUT BUT WILL SCATTER THROUGH MIDDAY. A COLD FRONT APPROACHES FROM OHIO WITH A LEADING BAND OF RAIN SHOWERS APPROACHING THE ALLEGHENY FRONT (ETA BETWEEN 11 AND NOON). BEHIND THE DEPARTING LOW AND AHEAD OF THE COLD FRONT...EXPECT SWLY FLOW WHICH WILL INCREASE TEMPS AND DEWPOINTS. MAX TEMPS BUMPED UP TO THE MID TO UPR 80S. THE INITIAL LINE APPROACHING FROM THE WEST WILL DISSIPATE AS IT MOVES EAST ACROSS THE ALLEGHENY FRONT. THERE SHOULD BE A LULL EARLY THIS AFTERNOON AS THE ATMOSPHERE RECHARGES...THEN SHOWERS AND UP TO SCATTERED THUNDERSTORMS WEST OF THE BLUE RIDGE...ISOLATED AT BEST EAST. THE LATEST HRRR RUNS (10 AND 11Z) HAVE STRUGGLED WITH THIS INITIAL BAND...BUT CONTINUE TO DEVELOP MORE ACTIVITY THIS EVENING. THE SEVERE THREAT LOOKS MINIMAL...BUT A MINOR WIND THREAT IS PRESENT WEST OF THE BLUE RIDGE. ISOLATED THUNDERSTORM ACTIVITY SHOULD PUSH EAST THROUGH THE BALT- WASH METRO THROUGH THE EARLY EVENING HOURS. NWLY FLOW INCREASES BEHIND THE FRONT...GUSTING 20 TO 25 MPH LATE TONIGHT THROUGH SUNRISE. NO FOG TONIGHT WITH MIXING...MIN TEMPS MID TO UPR 50S INLAND...LOW TO MID 60S NEAR SHORE. && .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/... HIGH PRESSURE WILL BUILD INTO THE MIDDLE ATLANTIC ON MONDAY BRINGING PLENTY OF SUNSHINE AND PLEASANT TEMPERATURES. AFTERNOON HIGHS MAINLY IN THE 60S TO LOWER 70S CAN BE EXPECTED ALONG WITH LOWS IN THE UPPER 30S TO LOW 40S WEST TO THE MID 40S TO 50S EAST OF THE BLUE RIDGE. && .LONG TERM /TUESDAY THROUGH SATURDAY/... SFC HIPRES WL BE ACROSS MOST OF THE ERN CONUS THRU THE END OF THE WK. H5 RDG WL BE BLDG TOO. AT FIRST GLANCE...THAT WUD SEEM LIKE A CUT-N-DRY FCST. HWVR...THERE IS A CATCH. ECMWF GDNC SUGGESTING A CUTOFF LOW IN THE MIDST OF THE H5 RDG...OR IN OTHER WORDS...A WEAKNESS IN THE HGT PTTN. THERE/S RATHER POOR AGREEMENT ON A FEATURE SO SUBTLE SVRL DAYS OUT. HWVR...SFC FLOW WL BE NLY TUE BUT VEER ELY WED-THU...AS THE CENTER OF THE SFC HIGH WL BE ATOP NEW ENGLAND/NYS BY THEN. AT THE VERY LEAST...CANNOT RULE OUT AN INCREASE IN MSTR AND MAYBE A SPRINKLE OR TWO /OR A PATCH OF DZ?/. SO AT THIS JUNCTURE...WL KEEP TUE SUNNY...BRING CLDS INLAND WED... AND OFFER UP SOME LOW END POPS /20-30 PCT/ WED NGT-THU. CHOOSING A STRATIFORM PCP CHARACTER. AM THINKING AS THE UPR RDG BLDS TO THE W OF THE AREA...THAT MAY BE ENUF TO ALLOW SFC RDGG TO RETROGRADE. IF THAT DOES HPPN...THEN WE/LL LOSE THE ONSHORE FLOW...AND THE MARINE AMS WL LOSE ITS GRIP ON THE RGN. DONT HV THE HIEST OF CONFIDENCE IN THIS OUTLOOK...BUT DONT WANT TO CARRY A PROLONGED PD OF LOW POPS UNDER HIPRES W/O A CLEARER SIGNAL. CAN SAY THIS...HIER HGTS WL LEAD TO WARMER TEMPS. MAXT TUE-THU NOT FAR OFF FM BAY WATER TEMPS...WHICH IS ABT 5 OR 6 DEGF COOLER THAN CLIMO. WE/LL BE BACK NEAR NORMAL AGN FRI-SUN. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/... SCATTERED SHOWERS AND THUNDERSTORMS WILL DEVELOP THIS AFTERNOON AND EVENING AHEAD OF A COLD FRONT...DECREASING TO ISOLATED THUNDERSTORMS FOR DC METROS DUE TO DOWNSLOPING WLY FLOW. ANY IMPACT TO THE DC METROS IS IN 21-00Z TIMEFRAME. NWLY FLOW BEHIND THE COLD FRONT GUSTS TO 20 KT...NO FOG EXPECTED TONIGHT. OUTLOOK... MON-TUE...VFR UNDER HIPRES. WED-THU...ONSHORE FLOW MAY BRING A STRATUS DECK INLAND. FLGT RESTRICTIONS PSBL...BUT CONFIDENCE LOW. && .MARINE... WINDS WILL REMAIN BELOW SCA LEVELS TODAY EXCEPT WHERE SHOWERS AND THUNDERSTORMS DEVELOP THIS EVENING. SCA CONDITIONS IN NWLY FLOW GUSTING TO 25 KT ARE EXPECTED BEHIND A COLD FRONT OVERNIGHT THROUGH MONDAY. NLY FLOW TUE WL VEER ELY FOR WED-THU. GDNC SUGGESTING ELY FLOW MAY BE STIFF...POTENTIALLY SUPPORTING SCA CONDS OVER A PORTION OF THE WATERS /MID BAY/. && .TIDES/COASTAL FLOODING... NLY FLOW HAS DECREASED DEPARTURES TO THREE QUARTERS OF A FOOT OR LESS. A BRIEF SOUTHERLY FLOW THIS EVENING MAY RAISE LEVELS AGAIN...SO SOME MINOR COASTAL FLOODING IS POSSIBLE WITH THE PREFERRED HIGH TIDE OVERNIGHT. A COLD FRONT COMES THROUGH LATE TONIGHT WITH GUSTY NWLY FLOW THAT WILL FURTHER DECREASE DEPARTURES. THIS IS A COMPLICATED ISSUE AND WILL BE CLOSELY MONITORED. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 4 AM TO 6 PM EDT MONDAY FOR ANZ530>543. && $$ SYNOPSIS...BAJ/HTS NEAR TERM...BAJ/KRW SHORT TERM...KRW LONG TERM...HTS AVIATION...BAJ/HTS/KRW MARINE...BAJ/HTS/KRW TIDES/COASTAL FLOODING...BAJ

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