Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 020800 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 400 AM EDT THU JUL 2 2015 .SYNOPSIS...
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A STATIONARY FRONT WILL REMAIN OVER CENTRAL VIRGINIA AND SOUTHERN MARYLAND THROUGH TODAY...AND LINGER OVER THE AREA THROUGH THE WEEKEND. WITH SEVERAL WAVES OF LOW PRESSURE WILL MOVE EAST ALONG THE FRONT AS AN ACTIVE PATTERN CONTINUES. HIGH PRESSURE WILL RETURN FOR THE FIRST HALF OF NEXT WEEK.
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&& .NEAR TERM /THROUGH TONIGHT/...
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LATEST SURFACE ANALYSIS SHOWS A COLD FRONT STRETCHING ACROSS CENTRAL/SOUTHERN VIRGINIA WITH HIGH PRESSURE OVER THE GREAT LAKES AND A WAVE OF LOW PRESSURE IN THE CENTRAL PLAINS. DEW POINTS HAVE LOWERED A BIT AS THE CANADIAN AIR HAS GRADUALLY PUSHED INTO THE REGION. OF NOTE IS THAT MUCH OF THE REDUCED VISIBILITY (REDUCED AS IN BELOW 10 MILES) BEING REPORTED ACROSS THE REGION IS PROBABLY DUE TO SOME CANADIAN WILDFIRE SMOKE WHICH HAS WORKED ITS WAY SOUTHWARD BEHIND THE FRONT. MOST GUIDANCE SHOWS THE FRONT STALLING OUT IN SOUTHERN VIRGINIA TODAY. ONE OR MORE WAVES OF WEAK LOW PRESSURE ARE ALSO PROGGED TO MOVE EASTWARD ALONG THE BOUNDARY LATER TODAY AND TONIGHT AS A COUPLE OF WEAK VORTICITY MAXIMA MOVE EAST ACROSS THE AREA IN THE FAST FLOW ALOFT. THE EXACT AMOUNT OF NORTHWARD MOTION WITH THE PRECIPITATION ASSOCIATED WITH EACH WAVE IS IN QUESTION...WITH THE MORE MESO-SCALE NAM AND RGEM KEEPING MOST OF THE PRECIPITATION SOUTH OF DC/BALTIMORE METRO CLOSER TO THE STALLED FRONTAL BOUNDARY THROUGH TONIGHT...WHILE THE GFS AND ECMWF ARE MORE GENEROUS AND BRING SOME SHOWERS INTO THE METRO. GIVEN UNCERTAINTY...KEPT POPS IN THE METRO AREAS BELOW 50 PERCENT. THERE IS SOME INSTABILITY...SO A FEW THUNDERSTORMS CAN`T BE RULED OUT ESPECIALLY THIS AFTERNOON AND EVENING...BUT WITH OUR REGION BEING ON THE NORTH SIDE OF THE FRONT THINK THEY SHOULD BE PRETTY ISOLATED WITH MOST ACTIVITY BEING OF THE NON- THUNDERY TYPE. HIGHS WILL BE SEVERAL DEGREES LOWER THAN YESTERDAY AND DEW POINTS WILL ALSO BE LOWER...BUT CLOUDS SHOULD BE MORE COMMON. LOWS TONIGHT WILL GENERALLY BE SIMILAR TO THIS MORNING`S.
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
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RIGHT NOW...THE BEST CHANCE OF PRECIPITAITON ACROSS THE AREA WOULD APPEAR TO BE FRIDAY...AS A DECENT SHORTWAVE AND VORT MAX MOVES ACROSS THE AREA SUPPORTING A MORE NOTABLE LOW PRESSURE WAVE AT THE SURFACE ALONG THE STALLED FRONT. UNCERTAINTY REMAINS AS TO HOW LONG IT LINGERS FRIDAY NIGHT...WITH SOME GUIDANCE ALLOWING IT TO PULL AWAY FAST ENOUGH SO THAT THE REGION DRIES OUT...WHILE OTHER MODELS KEEP THE SHOWERS OVER THE AREA. FOR NOW KEPT HIGHEST POPS DURING THE DAY...BUT THE POSSIBILITY OF DECENT PRECIPITATION DURING FRIDAY NIGHT IS DEFINITELY OF NOTE AND IF THERE IS BETTER CONSENSUS IN THE FUTURE...POPS MAY CERTAINLY END UP SIGNIFICANTLY HIGHER. TEMPERATURES WILL BE COOL FRIDAY WITH MANY AREAS FAILING TO REACH 80...WHILE LOWS WILL REMAIN SIMILAR TO RECENT DAYS. FOURTH OF JULY...STATIONARY FRONT LINGERING OVER THE AREA (WITH SHORTWAVES RIDING ALONG IT) MAKES FOR A COMPLICATED FORECAST. CONSENSUS AMONG 00Z GFS/ECMWF/NAM IS FOR A MORNING LOW TO CROSS SRN MD/WATERS WITH A SECONDARY SHORTWAVE TO CROSS THE POTOMAC HIGHLANDS LATE IN THE AFTERNOON. BOTH OF THESE FEATURES WILL SHIFT THE FRONTAL SYSTEM...TO AN UNCERTAIN EXTENT. FELT THE LIKELY POPS FOR THE SRN HALF OF THE CWA WAS A BIT HIGH...SO WENT CHANCE MOST PLACES IN THE AFTERNOON. WITH SHORTWAVE ENTERING THE WEST IN THE PEAK HEATING...WENT LIKELIES FOR THE POTOMAC/ALLEGHENY HIGHLANDS. MAX TEMPS LIMITED BY STRATO-CU AND ANY PRECIP...GENERALLY LOW 80S (WITH DEWPOINTS IN THE MID 60S...EXPECT A BIT OF A HEAT INDEX TO THE MID 80S). SATURDAY NIGHT...KEY FOR EVENING POP IS PROGRESSION OF WEAK SHORT WAVE FROM THE CENTRAL APPALACHIANS AND REMAINING INSTABILITY. THOSE DETAILS WILL BECOME MORE APPARENT WITH FUTURE MODEL RUNS...BUT CURRENT BEST GUESS IS TO HAVE SCATTERED THUNDERSTORM ACTIVITY CONTINUE.
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&& .LONG TERM /SUNDAY THROUGH WEDNESDAY/...
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FRONTAL BOUNDARY SOUTH OF THE AREA DRIFTS FARTHER SOUTH SUNDAY AND MONDAY AS UPR RIDGE BUILDS EAST OVER THE MIDWEST. ANY ISOLATED TO POSSIBLY SCATTERED THUNDERSTORMS BOTH DAY LOOK TO BE DIURNALLY DRIVEN. QUIET WX TUES UNDER HIGH PRESSURE AND NEAR NORMAL TEMPS. NEXT COLD FRONT APPROACHES REGION FROM THE MIDWEST WEDNESDAY AND SLOWS WITH MORE ACTIVE WEATHER INTO LATE NEXT WEEK.
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&& .AVIATION /08Z THURSDAY THROUGH MONDAY/...
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FAIRLY LIGHT WINDS FROM THE NORTH THIS MORNING SHIFTING EASTERLY BY TONIGHT. VFR CIGS AND VIS OUTSIDE OF ANY SHOWERS...POSSIBLY MVFR IN SHOWERS OR EVEN VERY BRIEF IFR IN A HEAVIER SHOWER OR THUNDERSTORM...BUT THESE SHOULD BE ISOLATED. NOTE THAT SOME DIFFUSE WILDFIRE SMOKE FROM CANADA IS LIKELY TO BE THE PRIMARY CAUSE OF THE SUB-10 MILE VISIBILITY REPORTS WE ARE SEEING AT MANY TERMINALS THIS MORNING. LOW PRESSURE MAY BRING SOME STEADIER RAIN TO THE REGION BY FRIDAY POSSIBLY INTO FRIDAY NIGHT...WITH POTENTIAL FOR A MORE SUSTAINED PERIOD OF MVFR OR EVEN IFR CIGS/VIS. TIMING AND NORTHWARD EXTENT OF THIS IS STILL IN QUESTION AND SO CONFIDENCE IS NOT HIGH. STATIONARY FRONT LINGERS JUST SOUTH OF DC METROS SATURDAY...BEFORE DRIFTING FARTHER SOUTH SUNDAY AND MONDAY. SCATTERED THUNDERSTORMS THROUGH SATURDAY INTO THE EVENING ACROSS THE TERMINALS. MORNING NELY FLOW 10 TO 15 KT AS LOW PASSES SRN MD. DIURNALLY ISOLATED SUN/MON. QUIET WX TUES.
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&& .MARINE...
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WINDS SHOULD STAY BELOW SCA LEVELS TODAY...WITH NORTHERLY WINDS BELOW 10 KNOTS GRADUALLY SHIFTING TO EASTERLY. A FEW HEAVIER SHOWERS OR EVEN AN ISOLATED THUNDERSTORM ARE POSSIBLE TODAY...WHICH COULD PRODUCE GUSTIER WINDS...BUT THINK THESE SHOULD BE UNCOMMON. WINDS MIGHT INCREASE TO SCA LEVELS LATER FRIDAY AND FRIDAY NIGHT AS A LOW PRESSURE WAVE PASSES BY TO THE SOUTH AND SOUTHEAST WITH MORE WIDESPREAD RAIN SHOWERS. CONFIDENCE IS NOT HIGH SO DID NOT ISSUE AN SCA JUST YET...BUT IT MAY BE NEEDED. WILL NEED TO WATCH A WEAK LOW PASS SRN MD SATURDAY MORNING FOR NELY GUSTS AROUND 20 KT. SCATTERED THUNDERSTORMS POSSIBLE ALL DAY/EVENING. LIGHT ONSHORE FLOW THEN SUNDAY AND MONDAY AS FRONT DIPS FARTHER SOUTH OF THE AREA. QUIET TUESDAY.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...BAJ NEAR TERM...RCM SHORT TERM...BAJ/RCM LONG TERM...BAJ AVIATION...BAJ/RCM MARINE...BAJ/RCM

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