Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 310852 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 352 AM EST SAT JAN 31 2015 .SYNOPSIS...
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HIGH PRESSURE BUILDS ACROSS THE REGION THROUGH TONIGHT. LOW PRESSURE WILL APPROACH FROM THE WEST SUNDAY...AND CROSS THE REGION SUNDAY NIGHT. HIGH PRESSURE WILL RETURN FOR THE FIRST HALF OF NEXT WEEK.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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HIGH PRESSURE UNDER A BUILDING RIDGE WILL BRING DRY AND INITIALLY WINDY CONDITIONS TO THE MID ATLANTIC. TWO THINGS FOR THIS MORNING...WIND CHILLS AND GUSTY WINDS. WIND CHILL ADVISORY FOR THE WESTERN SLOPES OF THE POTOMAC HIGHLANDS REMAINS IN EFFECT UNTIL 9 AM TO ACCOUNT FOR WIND CHILLS BETWEEN -10 AND -15 DEGREES. AS TEMPS WARM THIS MORNING...AND WINDS DIMINISH...EXPECTING WIND CHILL VALUES TO IMPROVE TO ABV ZERO BY MID MORNING. WHILE THE REMAINDER OF THE AREA IS NOT UNDER A WIND CHILL ADVISORY...AREAS ALONG THE MASON DIXON AND WEST OF THE BLUE RIDGE COULD SEE A BRIEF PERIOD OF WIND CHILL VALUES BELOW ZERO THRU 8 AM. AS FOR THE WINDS...EXPECTING GUSTS INTO THE 20S THROUGH DAYBREAK OVER EASTERN AREAS WITH THE POSITIONING OF THE LLJ AND THE TIGHTER PRESSURE GRADIENT...TEENS OR EVEN NO GUSTS TO THE WEST WHERE THE PRESSURE GRADIENT HAS SLACKEN. WINDS WILL GRADUALLY THEN DIMINISH THROUGHOUT THE DAY AS THE CENTER OF THE HIGH PASSES JUST TO THE SOUTH. AS THE WINDS BACK TO THE SOUTH...TEMPS WILL BEGIN A WARMING TREND...WITH MANY AREAS REACHING NEAR 30 TODAY...AND EVEN INTO THE MID 30S OVER CENTRAL VA.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
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SFC HIGH NUDGES EAST AS AN AREA OF LOW PRESSURE OVER THE SOUTHWESTERN US BECOMES ORGANIZED AND APPROACHES THE AREA FROM THE WEST. 00Z MODEL SUITE IN DECENT AGREEMENT WITH THE PLACEMENT OF THE LOW OVER KY BY 00Z MONDAY. DRY WX IN PLACE TONIGHT AS THE RIDGE BECOMES MORE ZONAL IN NATURE. PLENTY OF SUBSIDENCE ALOFT WILL KEEP SKIES MOSTLY CLEAR FOR THE FIRST HALF OF THE NIGHT...WITH INCREASING CLOUD COVER FOR THE SECOND HALF AHEAD OF THE LOW. THUS GENERALLY EXPECTING A QUICK DROP IN TEMPS THIS EVENING...WITH A MORE GRADUAL TREND FOR THE LATTER HALF OF THE NIGHT. INTRODUCED POPS INTO THE FAR NW AREAS BY DAYBREAK SUNDAY TO ACCOUNT FOR LIGHT PCPN DEVELOPMENT ALONG THE ISENTROPIC LIFT. AS THE LIFT PUSHES NORTH...ALONG WITH A SHORTWAVE ALOFT LIFTING ACROSS THE AREA INTO PA...SPREAD THE POPS TO THE EAST...MAINLY ALONG THE MASON-DIXON LINE. TEMPS BELOW FREEZING DURING THE MORNING SHOULD KEEP ANY PCPN IN THE FORM OF SNOW...WITH UP TO A COUPLE TENTHS OF AN INCH ACCUM PSBL. FOR THE AFTN...PCPN SPREADS EAST AND SOUTH...WITH ONLY SOUTHERN MD POSSIBLY STAYING DRY TILL SUN EVENING. P-TYPE FOR THE AFTN REMAINS TRICKY AS THE TRACK OF THE 850MB LOW NOW BRINGS 850MB TEMPS TO AROUND -2 DEGREES CELSIUS BY 18Z SUN...AND RIGHT NEAR FREEZING BY 00Z. BOTH THE NAM AND GFS BUFKIT SOUNDINGS INDICATING PCPN UP TO 18Z AS SNOW...BUT WITH THE WARMER LAYER ALOFT SNEAKING IN...COULD SEE A PERIOD OF SLEET MIXING IN...MAINLY OVER VA...AND EVEN POSSIBLY TRANSITIONING TO ALL RAIN OVER CENTRAL VA. THE ONE THING OF NOTE IS THAT WITH SFC TEMPS PUSHING ABV FREEZING AS WAA SETS UP WITH SOUTHERLY FLOW...THE FREEZING RAIN THREAT DURING THE DAY LOOKS TO BE MINIMAL. AREAS JUST NORTH OF BALTIMORE METRO COULD SEE HIGH TEMPS JUST HIT FREEZING...BUT WITH COLDER 850MB TEMPS THERE...GENERALLY SHOULD EXPECT SNOW AND NOT FZRA THRU 00Z MONDAY. FOR AREAS THAT REMAIN ALL SNOW OR MOSTLY SNOW FOR SUN AFTN...COULD SEE UP TO ONE INCH ACCUMULATION.
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&& .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
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THE SFC LOW PROGGED TO TRACK FM THE MID OHVLY TO THE NRN SXNS OF THE CWFA SUN NGT. THIS SOLN ON THE SAME PAGE AS THE PAST DAY OR SO OF FCST RUNS...AND REPRESENTS THE MORE NRN TRACK. THE H8 LOW ALSO A LTL FURTHER N...INTO CENTRL PA. GIVEN THIS SOLN...THERE WL BE NOTHING TO IMPEDE WARM AIR ALOFT FM OVERSPREADING CWFA. THEREFORE...XPCT MELTING OF SOME IF NOT ALL HYDROMETEORS. THE KEY WL BE SFC TEMPS. THATS PROVING A BIT TRICKIER...NOT IN THE OVERALL TREND /WHICH WL BE NON-DIURNAL WARMING/ BUT IN PEGGING SPECIFICS WRT SFC FRZG. AM NOT CONVINCED WE/LL BE ABLE TO SCOUR OUT ALL COLD AIR IN THE VLYS. AREA OF CONCERN STRETCHES ACRS NRN MD AND IN THE PTMC HIGHLANDS...AND INCLUDES THE BALT NRN BURBS/FREDERICK/I-81 N OF OKV. HV HELD ONTO PTYPE OF ZR/S IN THESE AREAS...W/ A CHGOVER TO RA S OF THERE. AM A BIT UNCERTAIN ABT LCL TEMPS FOR AN ADDTL SLIVER INCL HOWARD/MONTGOMERY/LOUDOUN CNTYS...BUT DONT HV ENOUGH HARD EVIDENCE TO PREVENT A FCSTD WARM-UP OVNGT. POPS WL BE AT THEIR HIEST OVNGT WHEN THE LOW TRACKS NEARBY...FLLWD BY A RELATIVELY PRONOUNCED CFP DURING THE MRNG COMMUTE. TEMPS SHUD BE STDY/FALLING MOST OF THE DAY...TEMPERED A PINCH BY COMPRESSIONAL WARMING IN NWLY FLOW. DUE TO THAT OFFSET...SHUD BE ABLE TO GET PCPN AWAY FM DC BEFORE THERMAL CONDS SUPPORT SNOW. ELSW...WL BE SWITCHING BACK TO A RA/SNW MODE AS CAA ALOFT WL BRING TEMPS BELOW FRZG ABV THE SFC. WL ALSO HV THE RETURN OF UPSLP SHSN...BUT AT THIS POINT AM KEEPING ONLY MINIMAL ADDTL ACCUMS. SPEAKING OF WHICH...DO NOT SEE SGFNT SNOW AMTS W/IN CWFA BASED ON CURRENT STORM TRACK. HELD NRN MD/PTMC HIGHLANDS HIER THAN LTST RAW GDNC WUD SUGGEST. CURRENT THINKING IS THAT FINAL TALLIES WUD BE BELOW WATCH/WRNG VALUES. SINCE FCST ERRING ON THE HIGH SIDE AND THAT DOESNT MEET WATCH CRITERIA...WL BE CONTG HWO MENTION ONLY. CWFA WL HV A CPL DAYS UNDER HIPRES. MON NGT-TUE WL BE ABNORMALLY COLD THO...AS H8 TEMPS BTTM OUT ARND -12C IN THE WAKE OF THE DEEPING CSTL LOW. LTST MOS GDNC A TOUCH WARMER FOR MON NGT MIN-T. THIS STILL SUGGESTS A LARGE SWATH OF CWFA /NRN MD AND W OF BLURDG/ WL START TUE IN THE SINGLE DIGITS...AND ALL BUT CENTRL VA WL BE STUGGLING TO RISE ABV FRZG TUE. RETURN FLOW WL REACH AREA TUE NGT THO...FOR A CONSIDERABLY WARMER WED. THERE MAY BE A WEAK...MOISTURE-STARVED SYSTEM DROPPING SWD FM THE NRN STREAM WED...WHICH CUD BE THE FOCUS FOR RIPPLES FM EWD THRU THE END OF THE WK. HV KEPT SOME CLDCVR TO ACCOMPANY FNT...BUT REMOVED PCPN. SIMILARLY...PRIND SUGGEST THE FNT WUD THEN SET UP FAR ENUF AWAY FM /IE...SE OF/ CWFA THU-FRI. THREAT OF PCPN LOOKS MINIMAL.
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&& .AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
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HIGH CONFIDENCE VFR CONDITIONS THROUGH SUN MORNING. NW FLOW WITH GUSTS 20-25 KTS WILL GRADUALLY DIMINISH TODAY...WITH GUSTS DROPPING INTO THE TEENS MID-LATE MORNING...THEN BCMG MORE OCNL IN NATURE FOR THE AFTN. WINDS SHOULD DROP BELOW 10 KTS 21-23Z...AND BCMG LIGHT/VRB TONIGHT. EXCEPTION...GUSTS ALREADY ENDED KCHO AND WILL BE OCNL IN NATURE THIS MORNING AT KMRB. S FLOW GENERALLY 10 KTS OR LESS SUN. PCPN COULD IMPACT KMRB AS EARLY AS 15Z...AS -SN...WITH PCPN BCMG MORE LIKELY FOR THE AFTN AT ALL TERMINALS. -RA/PL FOR KCHO...-SN/PL ELSEWHERE. ANY SNOW ACCUMS PRIOR TO 00Z MON WILL BE LESS THAN ONE INCH. IFR CONDS LKLY SUN NGT AS LOPRES TRACKS ACRS AREA. ITS LOOKING MORE LIKE A COLD RAIN FOR CHO/DCA. PTYPE AT BWI/IAD A LTL MORE UNCERTAIN...BUT RA SHUD DOMINATE. MRB STANDS BEST CHC AT RECEIVING WINTRY PCPN. CFP DURING MRNG PUSH. WL BE EXPERIENCING STRONG NWLY FLOW MOST OF THE DAY. VFR XPCTD MON NGT-WED.
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&& .MARINE...
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WINDS GRADUALLY DIMINISHING EARLY THIS MORNING. WILL BE CONVERTING GALE WARNING TO SCA TO ACCOUNT FOR OBS HAVING REPORTED FOR MULTIPLE HOURS OF GUSTS LESS THAN 34 KTS. SCA IN EFFECT FOR ALL WATERS THRU 19Z...THEN JUST ON THE CHESAPEAKE BAY AND SOUTHERN PORTION OF THE TIDAL POTOMAC TIL 23Z. SUB-SCA CONDITIONS THEN TONIGHT THRU SUNDAY. OF NOTE FOR THIS MORNING...WITH SUSTAINED WINDS ABV 20 KTS...SEAS AROUND 3 FT...AND AIR TEMPS IN THE 20S...PSBL LIGHT FREEZING SPRAY RESULTING IN MINIMAL ICE ACCUMS ON THE OPEN WATERS OF CHESAPEAKE BAY. LOPRES WL TRACK JUST BARELY N OF THE WATERS LT SUN NGT...FLLWD BY CFP MON MRNG. WINDS WL PICK UP ON MON. MIXED LYR WL EASILY SUPPORT SCA...AND MAY EVEN SUPPORT THE RETURN OF GLW. WL ADD THAT POTL TO SYN AND HWO. XPCT A GRDL DECREASE OF WINDS MON NGT. TUE AND WED SHUD BE QUIETER AS HIPRES SETTLES OVRHD.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...WIND CHILL ADVISORY UNTIL 9 AM EST THIS MORNING FOR MDZ501. VA...WIND CHILL ADVISORY UNTIL 9 AM EST THIS MORNING FOR VAZ503-504. WV...WIND CHILL ADVISORY UNTIL 9 AM EST THIS MORNING FOR WVZ501-503- 505-506. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EST THIS EVENING FOR ANZ530>534-537>543. SMALL CRAFT ADVISORY UNTIL 2 PM EST THIS AFTERNOON FOR ANZ535- 536.
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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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