Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 270755 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 355 AM EDT WED MAY 27 2015 .SYNOPSIS...
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HIGH PRESSURE WILL REMAIN OFFSHORE THIS WEEK. A SOUTHERLY FLOW WILL BRING WARM HUMID CONDITIONS TO THE MID ATLANTIC THROUGH SATURDAY. SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE EACH AFTERNOON AND EVENING. A WEAK COLD FRONT WILL APPROACH THE REGION THURSDAY BUT WASH OUT BEFORE IT MAKES IT THROUGH. A STRONGER COLD FRONT WILL ARRIVE SUNDAY.
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&& .NEAR TERM /THROUGH TONIGHT/...
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MAIN STORY TODAY WILL BE THE INCRSG LIKELIHOOD OF SHOWERS AND TSTMS BY THIS AFTN/EVENING...WITH THE POTENTIAL FOR SVR STORMS...MAINLY EAST OF A HAGERSTOWN TO DC TO SOUTHERN MD LINE. REGION REMAINS PLACED UNDER PERSISTING UPPER LVL RIDGE TODAY WHILE AN UPPER LVL TROUGH SWINGS THROUGH THE MIDWEST AND APPROACHES THE AREA BY TONIGHT. AT THE SFC...HIGH PRESSURE REMAINS ANCHORED OFFSHORE...THOUGH WILL WEAKEN ITS HOLD ON THE AREA THIS AFTN WITH THE FORMATION OF A LEE TROUGH EXPECTED BY THIS AFTN. WEAK SHORTWAVE RIDING THE RIDGE THIS MORNING IS RESULTING IN ON GOING CONVECTION OVER THE EASTERN OH RIVER VALLEY AS NOTED ON 07Z WATER VAPOR. EXPECTING THIS PCPN TO REACH THE FAR WESTERN AREAS NEAR DAYBREAK THIS MORNING. MAINLY SHOWERS THOUGH CANNOT RULE OUT AN ISO TSTM INITIALLY. INCRSG COVERAGE IN THE CONVECTION BY MIDDAY. THE QUESTION THE PAST FEW DAYS HAD BEEN HOW UNSTABLE THE ATMO WOULD BECOME THIS AFTN...AND AS A RESULT WHAT WOULD BE THE POTENTIAL FOR STRONGER TO SVR TSTMS. WHILE SHEAR HAS STRENGTHEN SLIGHTLY ON THE LATEST MODEL RUNS...GENERALLY AROUND 20-25 KTS...INSTABILITY REMAINS THE BIGGER PLAYER IN THE DEVELOPMENT OF THE STRONGER STORMS FOR TODAY. AXIS OF HIGHEST INSTABILITY ALIGNS ALONG THE LEE SFC TROUGH THIS AFTN...WITH THE THINKING THAT A THINNER LAYER OF CLOUDS WILL SET UP OVER THE EASTERN AREAS...LEADING TO BETTER DIURNAL HEATING. THE NAM...WITH THE TYPICAL HIGHER DEW PTS...HAS THE MUCH HIGHER SBCAPE VALUES...ABV 2000 J/KG FOR INSTANCE AT DCA. BUT EVEN THE GFS IS SHOWING AROUND 1000 J/KG...SO EVEN BEING CONSERVATIVE THERE IS A GOOD AMT INSTABILITY. GENERALLY THINKING THAT WITH THE NEAR UNIDIRECTIONAL WIND FLOW...WILL SEE DEVELOPMENT OF A LINE OF STORMS OVER CENTRAL MD MIDDAY UNDER THE RIGHT ENTRANCE REGION. AS THE LINE PUSHES EAST...EXPECTING IT TO HIT THE LEE TROUGH ALIGNED JUST EAST OF THE BLUE RIDGE...AND THOUGH LACKING ON THE SHEAR...THE INSTABILITY WILL BE ENOUGH TO TRIGGER STRONGER TO POSSIBLY EMBEDDED SVR STORMS. WITH THE LACK OF SHEAR...EXPECTING GUSTY TO DAMAGING WINDS TO BE THE MAIN THREAT WITH THESE STORMS. BY THIS EVENING...WITH LOSS OF SFC BOUNDARY AND INSTABILITY... EXPECTING THE PCPN TO TAPER OFF...WITH AREAS WEST OF THE BLUE RIDGE BCMG DRY DURING THE FIRST HALF OF THE NIGHT...AND EVERYWHERE ELSE BY THE SECOND HALF OF THE NIGHT. ANOTHER MILD NIGHT CAN BE EXPECTED WITH TEMPS IN THE 60S TO NEAR 70 IN THE MAIN METRO AREAS.
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&& .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
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ANOTHER DAY WITH SHOWERS AND TSTMS AS SFC LOW CURRENTLY OVER THE GREAT LAKES LIFTS TO THE NORTH AND EAST...DRAGGING ITS ASSOCIATED COLD FRONT INTO THE REGION BY THURS MORNING. HOWEVER...THE SFC HIGH AND UPPER LVL RIDGE WILL WORK TO STALL THE PROGRESSION OF THE FRONT...WITH IT BCMG NEARLY STATIONARY FOR MOST OF THURS ACROSS THE NORTHERN HALF OF THE CWA...EVENTUALLY WEAKENING BY THURS NIGHT. THIS SFC BOUNDARY WILL BE THE TRIGGER MECHANISM FOR ACTIVITY DURING THE DAY AS THE ATMO BECOMES DECENTLY UNSTABLE YET AGAIN WITH TEMPS PUSHING WELL INTO THE 80S AND DEW PTS PERSISTING IN THE 60S. WHILE THE INSTABILITY WONT BE NEAR THE LVLS AS TODAY...EXPECTING A BUT MORE SHEAR OVER THE AREA TO AID IN TSTM DEVELOPMENT. OVERALL SVR PARAMETERS ON THE WEAKER SIDE...AND WITH A LACKING OF UPPER LVL SUPPORT AS THE BETTER FORCING REMAINS NORTH OF THE AREA...NOT ANTICIPATING SVR OR EVEN STRONGER TSTM DEVELOPMENT. AS THE FRONTAL BOUNDARY DISSIPATES THURS NIGHT...ALONG WITH ANY DAYTIME RESULTING INSTABILITY...PCPN IS EXPECTED TO TAPER OFF FROM NORTH TO SOUTH. HAVE MAINTAINED AT LEAST SLIGHT CHC POPS THRU THE NIGHT EVERYWHERE...BUT THESE COULD VERY WELL BE OVERDONE...WITH THE PCPN TAPERING OFF SOONER. SLIGHTLY COOLER TEMPS THURS NIGHT BEHIND THE FRONT...STILL IN THE 60S THOUGH.
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&& .LONG TERM /FRIDAY THROUGH TUESDAY/...
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SFC TROFFING WILL BE SOUTH OF THE AREA BY FRI MRNG. ANY THERMAL DISCONTINUITY WUD HV WASHED OUT BY THEN...AND MID LVL HGTS START TO RISE ONCE AGN. THE BERMUDA HIGH TYPE SYNOP PTTN WL BE RETURNING IN RELATIVELY WK SFC FLOW. WL ONCE AGN HV THE RISK FOR DIURNALLY DRIVEN SHRA/TSTMS...BUT SUPPORT FOR NMRS OR MATURE STORMS SEEMS TO BE LACKING. HV POPS NO HIER THAN CHC...INITIATING IN THE HIER TRRN BY MID AFTN AND MIGRATING TWD THE COAST. HWVR...THE LOSS OF SUNSHINE SHUD SPELL THEIR DEMISE...AND POPS ALONG THE WRN SHORE OF THE BAY WL END UP LWR THAN INLAND AREAS. MAXT WL BE A CPL DEGF LWR THAN THU. WL BE KEEPING MIN-T IN THE MID-UPR 60S DUE TO DEBRIS CLDS. THAT CUD POTENTIALLY END UP BEING A PINCH TOO WARM BASED ON PROJECTED DEWPTS. A STRONGER CDFNT WL SLOWLY MARCH TWD THE AREA THIS WKND. WL BE IN THE SW FLOW AHD OF FNT SAT...W/ GREATER INSTABILITY BEING PULLED NWD AHD OF BNDRY. THE INSTBY AXIS WL REMAIN W OF THE MTNS...WHICH IS WHERE THE HIEST POPS WL BE PLACED /AIDED BY OROGRAPHIC LIFT/. IN ADDITION...SAT HAS THE BEST CHC AT REACHING 90F. FOR NOW WL BE HOLDING MAXT JUST SHY OF THAT. THE FNT WL BE DRAGGED ACRS AREA ON SUNDAY...W/ NRN STREAM LOPRES HEADING TWD THE CNDN MARITIMES. THAT WL MAKE THE ORIENTATION OF THE FNT MORE PERPENDICULAR TO UPR FLOW. EXACT TIMING STILL A BIT UP IN THE AIR...BUT RAFL RATES WL BE A CONCERN SINCE PWAT WL BE NEAR 2 INCHES. HV LKLY POPS AND SLGTLY LWR TEMPS. IN A PTTN SUCH AS THIS...ITS ALWAYS QSTNBL HOW FAR S FNT WL MAKE IT BEFORE STALLING/WASHING OUT. HV COOLER AIR IN FCST FOR MON-TUE...BUT AM NOT SURE WHETHER FOCUS FOR STORMS WL COMPLETELY PUSH THROUGH. THEREFORE...HV CHC POPS THRU XTNDD FCST.
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&& .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
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GENERALLY VFR CONDITIONS FOR THE TAF PERIOD. PSBL MVFR CIGS AROUND 12Z THIS MORNING WITH CIGS AROUND 2KFT CURRENTLY NOTED JUST TO THE SOUTH AND WEST. ANY MVFR CIGS EXPECTED TO SCATTER OUT BY 14/15Z...WITH SCT CU AND BKN-OVC MID LVL DECK THEN EXPECTED. MOD CONFIDENCE ON THE PCPN TIMING...COULD SEE +/- 1-2 HRS. WHILE CURRENTLY HAVE VFR CONDITIONS WITH THE VCTS MENTION...CANNOT RULE OUT MVFR OR LOWER CONDITIONS WITH ANY STRONGER TSTM...ESP DC/BALTIMORE METRO TAF SITES. SOME STORMS MAY ALSO PRODUCE GUSTY-STRONG WINDS AND HEAVY RAINS BRIEFLY. PCPN TAPERS OFF THIS EVENING...WITH DRY WX THEN TONIGHT. ANOTHER ROUND OF PCPN WILL BE PSBL ON THURS...BRINGING YET ANOTHER CHC FOR SUB-VFR CONDITIONS. WINDS GENERALLY SLY TODAY 8-10 KTS...BCMG LESS THAN 5 KTS TONIGHT. WINDS SHIFT TO THE NW TOMORROW...THOUGH STILL REMAINING LESS THAN 5 KTS. CHC OF SHOWERS/STORMS EXIST EACH DAY IN THE OUTLOOK...SPCLY DURING THE AFTN/EVE HRS. BEST CHC FOR STORMS WL BE ON SUNDAY. LCL FLGT RESTRICTIONS TO IFR OR LWR EXIST INVOF STORMS.
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&& .MARINE...
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SCA REMAINS IN EFFECT TODAY FOR ALL ZONES EXCEPT THE UPPER TIDAL POTOMAC. HAVE ADDED THE UPPER ZONE OF THE CHESAPEAKE BAY FOR THIS AFTN TO ACCOUNT FOR SLY CHANNELING. FOR THE LATTER HALF OF TONIGHT...ONLY KEEPING THE SOUTHERN CHESAPEAKE BAY ZONE...WITH SUB- SCA CONDITIONS THEN EXPECTED ON ALL WATERS BY THURS MORNING...LASTING THRU THURS NIGHT. TSTMS EXPECTED THIS AFTN COULD BRING PERIOD OF GUSTY TO STRONG WINDS. WINDS WL BE ON THE LIGHT SIDE ELY FRI...BUT S/SWLY FLOW WL REASSERT ITSELF BY AFTN-EVNG...CONTG THRU SAT. CHANNELING WL COME CLOSE TO SCA BY FRI EVNG...BUT THINK THAT SAT AFTN-EVE HAS A BETTER SCA RISK. CDFNT WL SAG ACRS AREA SUNDAY...MAKING FOR NMRS TSRA.
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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 MIDNIGHT EDT TONIGHT FOR ANZ531>533- 537>542. SMALL CRAFT ADVISORY UNTIL 6 AM EDT THURSDAY FOR ANZ534-543. SMALL CRAFT ADVISORY FROM NOON TODAY TO 8 PM EDT THIS EVENING FOR ANZ530.
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&& $$ SYNOPSIS...HTS NEAR TERM...SEARS SHORT TERM...SEARS LONG TERM...HTS AVIATION...SEARS/HTS MARINE...SEARS/HTS

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