Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 280512 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 112 AM EDT TUE APR 28 2015 .SYNOPSIS... AN UPPER LEVEL LOW PUSHES EAST ACROSS THE REGION THROUGH TUESDAY AS HIGH PRESSURE BRIEFLY BUILDS IN. LOW PRESSURE WILL IMPACT THE REGION MIDWEEK WITH HIGH PRESSURE RETURNING FOR THE WEEKEND. && .NEAR TERM /THROUGH TODAY/... UPPER LVL LOW REMAINS POSITIONED OVER THE CANADIAN MARITIMES THROUGH TONIGHT...EXTENDING BACK TO THE GREAT LAKES AND SOUTH INTO THE MID-ATLANTIC. S/WV ENERGY EMBEDDED WITHIN THE NLY FLOW HAS RESULTED IN WDLY SCT SHRA. HWVR...LLVL AMS DRY...WHICH HAS PRECLUDED MOST OF THIS MSTR FROM REACHING THE GROUND. AM NOTING A DOWNWARD TREND NOW THAT SUNSET HAS OCCURRED. BELIEVE THIS WILL CONTINUE...AND WILL RUN WITH A DRY FCST OVERNIGHT. CLOUDS WILL BE A BIT MORE SUBSTANTIVE THO...THEN PART IN THE WAKE OF THE VORT. IN TURN...THE CLDS WL KEEP TEMPS UP...WHICH IS REFLECTED IN LAMP GDNC. GOING TEMP FCST SEEMS TO BE ON TRACK. HV MADE NO TEMP CHGS...WHICH MEANS DO NOT BELIEVE THERE WL BE MUCH OF A FROST CONCERN IN THE CENTRAL SHEN VLY. && .SHORT TERM /TONIGHT THROUGH 6 PM WEDNESDAY/... UPPER LVL LOW PIVOTS OFF TO THE EAST TUES. HIGH PRESSURE BUILDS IN AT THE SFC...KEEPING THE AREA DRY. SUBSIDENCE BUILDING IN BEHIND THE DEPARTING LOW WILL HELP TO CLEAR SKIES TUES MORNING...BUT COULD SEE SCT CU BY TUES AFTN. DOWNSLOPING WINDS UNDER THE SCT SKIES WILL PUSH TEMPS INTO THE MID TO UPPER 60S. LOWS TUES NIGHT STAY IN THE 40S FOR MOST OF THE AREA...LIMITING THE FROST CONCERN. WEAK HIGH PRESSURE WILL BE OVER THE AREA EARLY WEDNESDAY. THE HIGH WILL MOVE OFFSHORE BY EARLY AFTERNOON...AND BE REPLACED BY A WAVE OF LOW PRESSURE DEVELOPING OVER THE APPALACHIANS. A SECOND AREA OF LOW PRESSURE WILL BECOME MORE ORGANIZED AS IT PASSES THROUGH NORTHERN FL AND MOVE OFFSHORE. CLOUDS WILL OVERSPREAD THE FORECAST AREA DURING THE DAY...WITH POTENTIAL FOR LIGHT RAIN DEVELOPING OVER PORTIONS OF THE HIGHLANDS...THE CENTRAL SHENANDOAH VALLEY AND THE CENTRAL FOOTHILLS. OTHERWISE DRY WX EXPECTED. RETURN FLOW IS EXPECTED TO DEVELOP FOR THE AFTERNOON WITH THE HIGH OFFSHORE. TEMPS SHOULD BE A FEW DEGREES WARMER THAN TUESDAY...WITH HIGHS MAINLY IN THE UPPER 60S AND LOW 70S. WEAK LOW PRESSURE PERSISTS OVER THE MTNS WED NIGHT. THE LOW THAT WAS OVER FL DURING THE DAY WILL MOVE OFFSHORE AND STRENGTHEN. THERE REMAINS SOME SPREAD AMONG MODELS ABOUT THE STRENGTH AND TRAJECTORY OF THIS SYSTEM...AND THEREFORE UNCERTAINTY ABOUT TIMING AND LOCATION OF RAINFALL ONSET OVERNIGHT. WILL CONTINUE WITH CHANCE POPS ACROSS THE FORECAST AREA FOR THE TIME BEING. LOWS FOR MOST AREAS WILL BE IN THE MID TO UPPER 40S...WITH LOW TO MID 50S LIKELY ALONG THE I-95 CORRIDOR. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... MODEL UNCERTAINTY STILL REMAINS RATHER LARGE WITH TRACK OF LOW PRESSURE MOVING OUT OF THE SOUTHEASTERN UNITED STATES DURING THE MIDDLE OF THE WEEK. DEPENDING ON WHICH MODEL OR EVEN MODEL CYCLE YOU CHOOSE...OUR AREA COULD SEE ANYWHERE FROM A COUPLE OF INCHES TO LESS THAN A HALF AN INCH OF RAINFALL. 00Z GFS MOST AGGRESSIVE WITH TRACK...WITH THE LOW HUGGING THE COASTLINE AS IT MOVES TO OUR EAST/NORTHEAST. HOWEVER...12Z GFS NOW IN BETTER AGREEMENT WITH 00Z ECMWF...AND KEEPS LOW FAR ENOUGH OFFSHORE THAT OVERALL IMPACTS TO OUR AREA ARE LESS. FOR NOW...LEANED MORE TOWARD THE 00Z ECMWF/12Z GFS SOLUTION DUE BETTER INITIALIZATIONS. WILL NEED TO MONITOR THIS CLOSELY AS A SMALL CHANGE IN THE TRACK COULD SIGNIFICANTLY CHANGE IMPACTS FOR OUR AREA. REGARDLESS OF WHAT HAPPENS WITH THE LATE WEEK SYSTEM...HIGH PRESSURE RETURNS THIS WEEKEND. TEMPS WILL BE ABOVE CLIMO AND PRECIP CHANCES WILL BE LOW. && .AVIATION /05Z TUESDAY THROUGH SATURDAY/... VFR CONDITIONS THRU THE TAF PERIOD. GUSTS HV DIMINISHED SOMEWHAT. WL HV NW FLOW THRU THE NGT WHICH WL CONT INTO TMRW. OCNL CIGS BKN-OVC050. PRIMARILY VFR WEDNESDAY. LIGHT NW WINDS IN THE MORNING BECOME SOUTHERLY IN THE AFTN. PSBL SUB-VFR WITH POTENTIAL RAIN DVLPG WED NIGHT. WINDS S-SW LESS THAN 10KT. UNCERTAINTY REMAINS LARGE WITH TRACK AND IMPACT OF LOW PRESSURE SYSTEM TRACKING ALONG COAST ON THU. THE MORE THE LOW HUGS THE COAST...THE GREATER THE AVIATION CONCERNS WILL BE. REGARDLESS...WOULD EXPECT SUB-VFR CONDITIONS IN ANY SHOWERS THAT OCCUR THU INTO FRI. && .MARINE...
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DUE TO GUSTS INXS OF 20KT ON THE CENTRAL PTMC HV XTND THE SCA TO THE UPR 2/3 OF THE PTMC THRU 6 AM. THIS MAY NEED TO BE XTND INTO THE DAYTIME HRS. CONT THE SCA THRU THE DAY TUE. STILL BELIEVE THAT SUB-SCA CONDITIONS ON ALL WATERS BY TUES EVENING. LIGHT NW WINDS ON THE WATERS WED MORNING...BECOMING S-SE 5-10KT BY THE AFTN. NO ADVISORIES XPCTD. LOW PRESSURE WILL EMERGE INTO THE ATLANTIC OFF THE FL COAST WED NIGHT AND STRENGTHEN AS IT BEGINS TO MOVE TO THE NORTH. WINDS BECOME SW AROUND 10KT...WITH POTENTIAL FOR SOME GUSTS UP TO 15KT. LIGHT RAIN PSBL. THE LOW PRESSURE SYSTEM TRACKING ALONG THE COAST THU INTO FRI HAS THE POTENTIAL TO CAUSE PERIODS OF SCA OR GALE CONDITIONS.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 4 PM EDT THIS AFTERNOON FOR ANZ530>534-537>543. SMALL CRAFT ADVISORY UNTIL 6 AM EDT EARLY THIS MORNING FOR ANZ535-536.
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&& $$ UPDATE...WOODY!

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