Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 271846 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 246 PM EDT MON APR 27 2015 .SYNOPSIS...
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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.
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&& .NEAR TERM /THROUGH TONIGHT/...
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UPPER LVL LOW REMAINS POSITIONED OVER THE CANADIAN MARITIMES THROUGH TONIGHT...EXTENDING BACK TO THE GREAT LAKES AND SOUTH INTO THE MID-ATLANTIC. A PASSING SHORTWAVE THIS MORNING BROUGHT BKN-OVC SKY CONDITIONS TO THE REGION. ANOTHER SHORTWAVE/VORT MAX CURRENTLY NOTED IN THE WATER VAPOR IMAGERY OVER OH/WV/PA WILL DIG SOUTH THROUGH THE REMAINDER OF THIS AFTN/EVENING. THIS ENERGY COMBINING WITH MINIMAL INSTABILITY COULD RESULT IN ISO-SCT RAIN SHOWERS...WITH LIGHT SNOW MIXING IN AT THE HIGHER ELEVATIONS OF THE POTOMAC HIGHLANDS. ANY PCPN THAT DOES OCCUR WILL TAPER OFF THIS EVENING...WITH THE ENTIRE AREA BCMG DRY FOR THE SECOND HALF OF THE NIGHT. ONLY OTHER CONCERN FOR TONIGHT WAS THE FROST POTENTIAL...MAINLY OVER THE SOUTHERN SHENANDOAH VALLEY AREAS. CURRENT FORECAST DROPS OVERNIGHT LOWS INTO THE MID TO UPPER 30S MAINLY...WITH ISOLATED SPOTS NEARING FREEZING. THINKING THE WINDS SHOULD STAY ELEVATED ENOUGH AND THE CLOUDS CLEAR OUT LATE ENOUGH TO KEEP TEMPS AS FORECASTED. HOWEVER...IF THE TREND THIS EVENING LOOKS TO HAVE CLEARING QUICKER AND/OR WINDS DROPPING MORE...COULD SEE THE NEED FOR A FROST ADVISORY IN AUGUSTA/ROCKINGHAM/NELSON. COUNTIES TO THE WEST ARE YET TO ENTER THE GROWING SEASON.
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&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
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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.
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&& .LONG TERM /THURSDAY THROUGH MONDAY/...
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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.
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&& .AVIATION /19Z MONDAY THROUGH SATURDAY/...
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VFR CONDITIONS THRU THE TAF PERIOD. BRIEF RAIN SHOWER PSBL THIS AFTN...MAINLY 19-22Z...WITH MINIMAL CATEGORICAL IMPACTS. OCNL GUSTS PSBL LATE THIS AFTN...WITH THE GUSTS ENDING 23-02Z THIS EVENING. OCNL GUSTS WILL BE PSBL AGAIN AT KBWI/KMTN ON TUES. 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.
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&& .MARINE...
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SCA REMAINS IN EFFECT THROUGH THIS EVENING FOR ALL WATERS...THEN CONTINUES ON THE CHESAPEAKE BAY AND SOUTHERN TIDAL POTOMAC THROUGH TUES AFTN. 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... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 4 PM EDT TUESDAY FOR ANZ530>534- 537>543. SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR ANZ535- 536. && $$ SYNOPSIS...SEARS NEAR TERM...SEARS SHORT TERM...SEARS/KS LONG TERM...MSE AVIATION...SEARS/KS/MSE MARINE...SEARS/KS/MSE

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