Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 040738 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 338 AM EDT MON MAY 4 2015 .SYNOPSIS...
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HIGH PRESSURE OFF THE CAROLINA COAST WILL SETTLE OFFSHORE THROUGH TONIGHT. A COLD FRONT APPROACHES LATE TUESDAY...STALLING ACROSS THE MID ATLANTIC THROUGH MIDWEEK. HIGH PRESSURE IS EXPECTED TO RETURN TO THE REGION LATE IN THE WEEK WHILE LOW PRESSURE DEVELOPS OFF THE CAROLINA COAST.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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SFC HIGH PRESSURE CURRENTLY OFF THE CAROLINA COAST WILL PUSH OFFSHORE TODAY...SETTLING TO THE EAST BY TONIGHT. AS THE REGION REMAINS ON THE WESTERN PERIPHERY OF THE HIGH...S-SW FLOW WILL BE PERSISTENT. WAA ON THIS FLOW WILL RESULT IN A GOOD WARM UP FOR THE AREA...WITH MOST OF THE AREA REACHING THE 80S...THE EXCEPTION BEING THE HIGHER ELEVATIONS OF THE POTOMAC HIGHLANDS. ALL MESO MODELS SUGGESTING ISO PCPN DEVELOPMENT OVER THE FAR SOUTHWESTERN CORNER OF THE CWA LATE IN THE DAY/DURING THE EVENING...WITH THE SUGGESTION OF A SFC TROUGH EXTENDING ACROSS EASTERN WV. HAVE INCLUSION OF LOW END SLIGHT CHC POPS TO ACCOUNT FOR ANY DEVELOPMENT THAT MAKES IF OVER THE RIDGE LINE. ANYTHING THAT DOES FORM WILL BE VERY LIGHT IN NATURE AND SHORT LIVED.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY NIGHT/...
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ANY LINGERING PCPN THIS EVENING WILL QUICKLY DIMINISH WITH LOSS OF DAYTIME HEATING. DRY WX THEN EXPECTED THRU MOST OF THE NIGHT. LOW PRESSURE TREKKING THRU SOUTHERN CANADA WILL DRAG ITS ASSOCIATED COLD FRONT CLOSE TO THE REGION TONIGHT...WITH THE FRONT STRADDLING PA BY 12Z TUES. WILL INTRODUCE POPS AROUND DAYBREAK NEAR THE MASON-DIXON LINE OF WESTERN MD TO ACCOUNT FOR THE FRONTS PLACEMENT AS WELL AS A WEAK SHORTWAVE/VORT MAX EXPECTED TO MOVE THRU TUES MORNING. THE COLD FRONT NUDGES SOUTH DURING THE DAY...EVENTUALLY STALLING JUST SOUTH OF THE MASON-DIXON LINE THRU TUES NIGHT. NEAR ZONAL FLOW SETS UP ALOFT...SO EXPECTING ANY PCPN DEVELOPMENT TUES TO BE CONFINED NEAR THE FRONTAL BOUNDARY WITH THE BEST SFC CONVERGENCE. HAVE CHC POPS IN OVER NORTHERN AREAS...TAPERING OFF TO THE SOUTH...WITH POTENTIAL FOR SOME AREAS OF THE PIEDMONT TO REMAIN DRY THRU THE PERIOD. WITH HIGHS PUSHING INTO THE 80S YET AGAIN...AND SW FLOW INJECTING IN MORE MOIST AIR...MINIMAL INSTABILITY IS PSBL. SHEAR AND LAPSE RATES ARE ON THE WEAKER SIDE...BUT ENOUGH WITH THE INSTABILITY TO TRIGGER AN ISO TSTM. SO WILL HAVE THUNDER MENTION FOR TUES AFTN. WITH THE LOSS OF DAYTIME HEATING...WILL KEEP THUNDER MENTION OUT FOR TUES NIGHT. POPS DECREASE SECOND HALF OF TUES NIGHT.
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&& .LONG TERM /WEDNESDAY THROUGH SUNDAY/...
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CDFNT WL CONT TO SAG INTO AND PERHAPS THRU CWFA WED...WHICH WL PROVIDE SRN CNTYS WITH A BETTER CHC AT SEEING PCPN. HWVR...THE FNT WL BE BUMPING INTO THE H5 RDG...SO NOT ONLY WL SRN PROGRESS BE SLOW BUT ALSO SUSPECT THERE WL BE A WEAKENING TREND. THEREFORE WL NOT BE GOING W/ POPS HIER THAN CHC. SUCH A BAROCLINIC ZONE IN A SUMMER AMS WL YIELD A LTL INSTBY...BUT THAT WL BE UNDERCUT BY ELY SFC FLOW. AM KEEPING SCHC THUNDER IN GRIDS BUT DO NOT BELIEVE ANY STORMS WL BE A REALLY BIG DEAL. TAPERED MAXT BACK A PINCH DUE TO THE MARITIME INFLUENCE... BUT TIMING OF NOT JUST THE FNT BUT ALSO THE WINDS AND ANY PCPN WL UNLIMATELY DETERMINE THE MAXT OUTCOME. FNT LOOKS TO WASH OUT THU...W/ RDGG MAINTAINING ITS INFLUENCE THRU SAT. DRY FCST. TEMPS ON THE WARM SIDE...AND REFLECTS ADDTL WARMING DAILY. THERE WL BE MORE CLDS ON THU DUE TO RESIDUAL MSTR...BUT WL BE PTSUN AT WORST FOR CENTRAL VA/SRN MD. OTRW...MOSUN-SUNNY THRU THE PD. NEXT FNT MAY ARRIVE BY SUNDAY.
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&& .AVIATION /08Z MONDAY THROUGH FRIDAY/...
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VFR CONDITIONS FOR THE TAF PERIOD. OCNL GUSTS PSBL THIS AFTN...MAINLY KIAD/KBWI/KMTN...THOUGH STAYING GENERALLY LESS THAN 20 KTS. SLY FLOW WILL BECOME SW-W BY TUES MORNING. ANY PCPN TODAY/TONIGHT SHOULD REMAIN WELL WEST OF THE TAF SITES. INCRSG CHC OF SHOWERS AND MAYBE AN ISO TSTM ON TUES...MAINLY AFTR 18Z FOR ALL SITES EXCEPT KCHO. LCL FLGT RESTRICTIONS PSBL INVOF SHRA WED...OTRW VFR THRU THE END OF THE WEEK.
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&& .MARINE...
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SUB-SCA CONDITIONS INITIALLY THIS MORNING. INCRSG SLY FLOW TODAY SHOULD RESULT IN ENOUGH OF A TUNNELING EFFECT TO PRODUCE GUSTS TO 20 KTS FOR THE CHESAPEAKE BAY AND LOWER TIDAL POTOMAC WATERS. SCA IN EFFECT FOR THESE ZONES BEGINNING THIS AFTN TO ACCOUNT FOR THIS. FOR TONIGHT...WINDS EXPECTED TO DIMINISH TO SUB-SCA OVER THE NORTHERN CHESAPEAKE BAY...AND THEN THE LOWER TIDAL POTOMAC BY TOMORROW MORNING. WILL CONTINUE SCA FOR THE MID CHESAPEAKE ZONE THRU TUES MORNING...WITH PSBL EXTENSION INTO TUES IF WINDS ARE SLOW TO SHIFT TO A WEST COMPONENT. SUB-SCA CONDITIONS ALL WATERS FOR TUES NIGHT. ELY FLOW BHD A CDFNT DROPPING SLOWLY SWD WED. MAY HV A BREIF SURGE IN WIND SPDS...BUT MIXING SHUDNT BE THAT GREAT. WL BE CAPPING WINDS AT 15 KT. AFTER THAT...WINDS WL BE ON THE LIGHTER SIDE ONCE AGAIN /AOB 10 KT/ UNDER A RIDGE AXIS.
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&& .CLIMATE... ONE OF THE WARMEST AIRMASSES SO FAR THIS YEAR IS EXPECTED TO MOVE OVER THE AREA DURING THE FIRST HALF OF THE UPCOMING WEEK. BELOW IS A LIST OF THE LAST TIME A HIGH TEMPERATURE OF 85 DEGREES OR HIGHER WAS OBSERVED. SITE..LAST 85+ DEGREE DAY... DCA...SEPTEMBER 27TH 2014... BWI...SEPTEMBER 11TH 2014... IAD...SEPTEMBER 11TH 2014... CHO...SEPTEMBER 21ST 2014... DMH...SEPTEMBER 11TH 2014... HGR...SEPTEMBER 6TH 2014.... MRB...SEPTEMBER 21ST 2014... && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 6 AM EDT TUESDAY FOR ANZ531>534-537-540-541-543.
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&& $$ SYNOPSIS...SEARS/HTS NEAR TERM...SEARS SHORT TERM...SEARS LONG TERM...HTS AVIATION...SEARS/HTS MARINE...SEARS/HTS CLIMATE...DH

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