Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 010856 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 356 AM EST SUN FEB 1 2015 .SYNOPSIS...
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LOW PRESSURE MOVES THROUGH THE REGION THROUGH MONDAY. HIGH PRESSURE WILL RETURN FOR THE FIRST HALF OF THE WEEK. A COLD FRONT IS EXPECTED TO MOVE INTO THE REGION WEDNESDAY NIGHT.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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SFC HIGH PUSHING EAST THIS MORNING AS THE NEXT LOW PRESSURE SYSTEM APPROACHES FROM THE WEST. LIGHT RETURNS CURRENTLY APPEARING ON RADAR JUST TO THE WEST...ASSOCIATED WITH THE INITIAL SURGE OF ISENTROPIC LIFT AND A PASSING SHORTWAVE. HOWEVER...HIGH DEW PT DEPRESSIONS RIGHT NOW SHOULD KEEP ANYTHING FROM REACHING THE GROUND. HAVE SLIGHT CHC POPS FOR LIGHT SNOW OVER THE WESTERN ALLEGHENY FRONT...BUT NO ACCUMULATION REALLY EXPECTED. HEADING INTO TODAY...SOME DISCREPANCIES IN THE MODELS ON THE HANDLING OF THE PCPN. THERE CONTINUES TO BE SOME SUGGESTION OF PCPN DEVELOPMENT LATER THIS MORNING/EARLY AFTN...WHICH IF IT DOES OCCUR...WOULD BE IN THE FORM OF LIGHT SNOW. HOWEVER...AGAIN A VERY DRY AIRMASS NEEDS TO BE OVERCOME. SOUTHERLY FLOW SETS UP...BUT IS WEAK...AND WITH THE LLJ NOT IN PLACE TILL TONIGHT...IT COULD VERY WELL END UP BEING DRY ACROSS MUCH OF THE AREA DURING THE DAY. BEST CHC FOR ANY PCPN WOULD BE ALONG THE MASON-DIXON LINE AND WEST OF THE BLUE RIDGE. HIGHER CONFIDENCE OF PCPN MOVING IN BY LATE THIS AFTN...AND HAVE SPREAD POPS EAST AND SOUTH TO ACCOUNT FOR THIS. AS FOR P-TYPE...A GOOD SURGE OF WAA FINALLY ARRIVES WITH THE SOUTHERLY FLOW...WHICH WILL WORK TO PUSH BACK THE SNOW/RAIN LINE TO THE NORTH. INITIALLY SHOULD SEE SLEET MIXING IN...THINKING MAINLY 20-00Z TIME PERIOD...AS 850MB TEMPS WARM UP QUICKER THAN SFC TEMPS. AREAS ALONG THE MASON-DIXON LINE EXPECTED TO REMAIN SNOW...WITH UP TO AN INCH OF SNOW PSBL.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
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LOW PRESSURE MOVES INTO THE OHIO RIVER VALLEY BY 06Z THIS EVENING...WITH THE BIGGEST SURGE OF WAA AND MOISTURE RIDING THE SOUTHERLY FLOW OUT AHEAD OF THE LOW. THIS EVENING WILL BE THE BIGGEST TRANSITION PERIOD FOR PCPN...AND ALSO THE LOWEST CONFIDENCE OF P-TYPE AS THERE REMAINS SOME QUESTION AS TO HOW QUICKLY THE WARMER AIR CAN ERODE THE PERSISTING COLD AIR...ESPECIALLY ALONG THE MASON-DIXON LINE. USING A COMBINATION OF THE 00Z GFS AND NAM BUFKIT SOUNDINGS...CONTINUED WITH THE MENTION OF FZRA CENTRAL AND WESTERN MD...AND SOUTH INTO PORTIONS OF NORTHERN VA AND NORTHERN PARTS OF DC METRO...WHERE TEMPS ARE HOVERING RIGHT NEAR FREEZING. CONFIDENCE WOULD LEAN THAT IF ANYTHING THE TEMPS WARM UP QUICKER...AND THUS A SHORTER TIME PERIOD OF FZRA. BUT WITH THE POTENTIAL FOR AT LEAST A PERIOD OF FZRA RESULTING IN A TRACE TO A COUPLE HUNDREDTHS OF AN INCH OF ICE...HAVE GONE AHEAD AND EXTENDED THE WINTER WEATHER ADVISORY TO INCORPORATE NW HOWARD...NW MONTGOMERY...WESTERN LOUDOUN...AND THE REMAINDER OF THE EASTERN WV PANHANDLE...AS WELL AS HAMPSHIRE...FREDERICK VA...AND CLARKE. WHILE THE TIMING OF THE ADVISORY CURRENTLY EXISTS FROM THIS AFTN THROUGH TONIGHT...THE MAIN POTENTIAL FOR ICE ACCUM WILL BE BETWEEN 23-09Z TONIGHT. ELSEWHERE...PCPN CHANGES OVER TO ALL RAIN AS 850MB TEMPS WARM WELL INTO THE SINGLE DIGITS ABV ZERO...AND BUFKIT SOUNDINGS INDICATING WET BULBING FINALLY BEING ACHIEVED BY 06Z. WITH MULTIPLE SHORTWAVES WORKING THROUGH TONIGHT AS THE SFC LOW PASSES OVER THE MID-ATLANTIC...CAN EXPECT PERIODS OF MODERATE TO HEAVY PCPN. THE SFC LOW PUSHES OFF THE NJ COAST BY MIDDAY MONDAY...WHILE THE STRONG UPPER LEVEL TROUGH FINALLY SWINGS THROUGH THE REGION MONDAY AFTN. CONTINUED POPS EVERYWHERE FOR MONDAY MORNING...THEN TAPERED OFF FROM WEST TO EAST...WITH THE THINKING ALL PCPN SHOULD CLEAR THE AREA BY MONDAY EVENING EXCEPT WITH THE CHC FOR UPSLOPE SNOW SHOWERS. STRONG SURGE OF CAA WITH THE NW FLOW ON THE BACKSIDE OF THE LOW WILL INCREASE WINDS BY MONDAY AFTN...WITH GUSTS INTO THE 20S. THIS WILL ALSO RESULT IN A NON-DIURNAL TEMP TREND...MAINLY FOR WESTERN AREAS AS THEY WILL SEE THEIR DAYTIME HIGHS IN THE MORNING. OVER THE EASTERN AREAS...BEFORE THE CAA MOVES IN...COULD SEE HIGHS IN THE UPPER 40S.
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&& .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
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STRONG NW FLOW KICKS IN MON EVENING AS CSTL LOW BOMBS OUT OFF CAPE COD. THE COMBO OF A TIGHTENING P-GRAD AND GOOD MIXING FM CAA WL EASILY PROVIDE MEAN MIXED LYR WINDS GREATER THAN 30 KT. THIS GRADIENT WL BE SUBSIDING/DCPLG SLIGHTLY THRU THE EVNG...BUT IT WL STILL BE A BRZY /AND CHILLY/ NGT. SCT LINGERING UPSLP SHSN AT START OF PD WL DIMINISH AS HIPRES BLDS. WL HV PT-MOCLDY INTHE MTNS BUT CLR ELSW. TEMP GDNC NOT QUITE AS COLD AS PRVS RUNS. WL LEAN ON THE COOLER SIDE OF LTST DATA. WIND CHILLS NOT TO ADVY LVL...BUT SINGLE DIGITS SHUD BE COMMON. HIPRES WL BE NEARBY TUE...W/ RETURN FLOW BGNG TUE NGT. H8 THERMAL TROF STILL AN INFLUENCE TUE /-10 TO -12C/. MAXT ADJUSTMENTS MINIMAL...MAYBE A DEGF OR TWO HIER ACRS MD/NRN VA. CENTRL VA THE ONLY PLACE THAT SAFELY WL GET ABV FRZG. MIN-T TUE NGT WONT BE QUITE AS HARSH...DUE PARTLY TO A BLDG MID CLD DECK. LOPRES IN THE NRN STREAM DROPS FM S-CENTRAL CNDA ACRS NEW ENGLAND WED-WED NGT. ITS NOT EXACTLY CLEAR HOW MUCH MSTR WL BE ASSOCD W/ IT...BUT FOR THE MID ATLC ITS OUTPACING ANY UPA SUPPORT. THEREFORE WL BE BANKING ON A SYSTEM THAT WL BE STRUGGLING TO PRODUCE PCPN ON ITS OWN. AFTER A RELATIVELY MILD DAY WED...WL BE KEEPING SCHC SNW CONFINED TO THE MTNS WED NGT. TEMPS WL BE DROPPING THU /15 DEGF COOLER THAN MAXT WED/...WHICH CUD PROVIDE AN ENVIRONMENT FOR DIURNAL SHSN. TOO FAR OUT TO PINPOINT CVRG...BUT IT WUD BE A SITUATION FOR BRIEF...MINIMAL ACCUM /IF ANY/...BUT SUDDEN ONSET SHSN. WL HV MID-RANGE CLDS AND LOW END POPS. HIPRES SHUD CLOSE OUT THE WEEK. NO OTHER HAZARDS ANTICIPATED ATTM. TEMPS GRADUALLY MODERATING TWD CLIMO...BUT NOT SURE IF WE WL GET THERE.
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&& .AVIATION /09Z SUNDAY THROUGH THURSDAY/...
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VFR CONDITIONS THIS MORNING. CONDITIONS DIMINISH AS THE PCPN MOVES IN...WITH IFR BCMG LIKELY BY SUN NIGHT WITH THE HEAVIEST PCPN. INITIAL PCPN -SN/PL/RA MIX...BCMG ALL RAIN TONIGHT EVERYWHERE. TRANSITION TIMING IN TAFS COULD BE +/- 2 HOURS. ANY SNOW ACCUMS AT THE TERMINALS TODAY WOULD BE LESS THAN ONE INCH. S WINDS LESS THAN 10 KTS TODAY/TONIGHT WILL SHIFT TO THE NW MONDAY AND INCREASE...WITH GUSTS MIXING IN BY MONDAY AFTN. VFR CONDITIONS AS WELL BY MONDAY AFTN AS THE PCPN EXITS THE REGION. VFR SHUD PREVAIL MON NGT THRU AT LEAST WED. BIGGEST IMPACT WL BE THE WINDS MON NGT...WHICH WL BE FM THE NW AND MAY GUST UP TO 35-40 KT DURING THE EVNG PUSH. ANOTHER CDFNT WL CROSS LT WED. MAY HV WIDELY SCT SHSN REDUCING VSBY ON THU...ALONG W/ MORE GUSTY WINDS.
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&& .MARINE...
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SUB-SCA CONDITIONS ON ALL THE WATERS THROUGH 06Z TONIGHT. HAVE ISSUED A SCA OVER THE CENTRAL CHESAPEAKE BAY AND THE LOWER UPPER TIDAL POTOMAC TO ACCOUNT FOR INCREASING SOUTHERLY FLOW LATE TONIGHT...AND THEN NW FLOW BY TOMORROW AFTN. PSBL LULL IN THE SCA GUSTS AS THE WINDS SHIFT...BUT THIS WILL BE SHORT LIVED. AS CSTL LOPRES STRENGTHENS LT MON...IT WL INCREASE THE P-GRAD. COMBINED W/ DEEPENING FVRBL MIXING IN CAA...WINDS SHUD EXHIBIT A MARKED INCREASE LATE MON AFTN INTO MON NGT. WL HV MEAN 35-40 KT W/IN THE MIXED LYR. HV RAISED GLW FOR THE 2ND HALF OF THE AFTN INTO THE EVNG. SCA CONDS WL CONT THEREAFTER...AND MAY LEAK INTO TUE. BLDG HIPRES WL GRDLY RESULT IN DIMINISHING WINDS.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...WINTER WEATHER ADVISORY FROM NOON TODAY TO 8 AM EST MONDAY FOR MDZ003-501-502. WINTER WEATHER ADVISORY FROM 3 PM THIS AFTERNOON TO 8 AM EST MONDAY FOR MDZ004>006-503-505-507-508. VA...WINTER WEATHER ADVISORY FROM NOON TODAY TO 8 AM EST MONDAY FOR VAZ028-031. WINTER WEATHER ADVISORY FROM 3 PM THIS AFTERNOON TO 8 AM EST MONDAY FOR VAZ505. WV...WINTER WEATHER ADVISORY FROM NOON TODAY TO 8 AM EST MONDAY FOR WVZ050>053-503-504. MARINE...GALE WARNING FROM 3 PM MONDAY TO 1 AM EST TUESDAY FOR ANZ530>543. SMALL CRAFT ADVISORY FROM 1 AM TO 3 PM EST MONDAY FOR ANZ533- 534-537-542-543.
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&& $$ SYNOPSIS...SEARS/HTS NEAR TERM...SEARS SHORT TERM...SEARS LONG TERM...HTS AVIATION...SEARS/HTS MARINE...SEARS/HTS

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