Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 280229 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 929 PM EST TUE JAN 27 2015 .SYNOPSIS... STRONG LOW PRESSURE WILL CONTINUE TO TRACK NORTHEAST OFF THE NEW ENGLAND COAST INTO WEDNESDAY. HIGH PRESSURE WILL BUILD INTO THE MID ATLANTIC STATES THROUGH WEDNESDAY NIGHT. A COLD FRONT WILL APPROACH FROM THE OHIO VALLEY THURSDAY...THEN PASS ACROSS THE REGION THURSDAY NIGHT. HIGH PRESSURE RETURNS FRIDAY AND REMAINS THROUGH SATURDAY NIGHT...BEFORE LOW PRESSURE APPROACHES REGION LATE SUNDAY. && .NEAR TERM /THROUGH WEDNESDAY/...
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THE DEEP LOW PRESSURE SYSTEM IS SLOWLY PULLING NE FROM CAPE COD THIS EVENING WHILE HIGH PRESSURE BUILDS INTO THE WESTERN GREAT LAKES. ALTHOUGH THE ATMOSPHERE IS DRYING...THE MID ATLANTIC REMAINS UNDER THE INFLUENCE OF THE PRESSURE GRADIENT FROM THE LOW AS WELL AS STRANDS OF VORTICITY ROTATING AROUND THE UPPER LEVEL SYSTEM. CLOUDS HAVE SHOWN A SLOW EROSION TREND...ALTHOUGH IT LOOKS LIKE THEY COULD HANG ON A LITTLE LONGER THAN EXPECTED. THIS SHOULD HAVE MINIMAL EFFECT ON TEMPERATURES AS FALLS WILL BE DRIVEN BY CAA IN THE GUSTY NW WINDS. WITH LOWS EXPECTED IN THE TEENS TO NEAR 20...ANY LINGERING MOISTURE ON UNTREATED ROADS WILL REFREEZE. HAVE ISSUED AN SPS HIGHLIGHTING THIS ISSUE. WIND CHILLS WILL DROP TO THE SINGLE DIGITS IN THE NORTH AND TEENS IN THE SOUTH...WITH PERHAPS SOME OF THE MOUNTAIN TOPS SLIGHTLY BELOW ZERO. VSBY ARE IMPROVING IN THE UPSLOPE AREAS...SO THE SNOW INTENSITY IS LIKELY DECREASING. THIS TREND IS EXPECTED TO CONTINUE AS THE ATMOSPHERE DRIES OUT FURTHER TONIGHT. HOWEVER...RECENT HIGHWAY CAMERAS HAVE SHOWN SNOW COVERED ROADS IN THE HIGH TERRAIN...SO WILL ALLOW THE WINTER WX ADVISORY TO CONTINUE UNTIL 1 AM. THE START OF WEDNESDAY WILL BE MET W/ CLEAR SKIES AND STILL BLUSTERY CONDITIONS. WIND CHILL VALUES AROUND DAWN WILL STILL BE IN THE SINGLE DIGITS AND TEENS. ALTHOUGH STILL QUITE COLD...TEMPS WILL QUICKLY JUMP BACK INTO THE 20S AND L30S BY LATE MRNG. NOT ENOUGH TIME IN THE DAY HOWEVER TO GET MUCH ABOVE FREEZING...ESPEC W/ NW WINDS CONTINUING TO GUST IN THE 15-25MPH RANGE.
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&& .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... RIDGING WILL MOVE OVER THE MID-ATLANTIC WEDNESDAY NIGHT AND SFC HIGH PRESSURE WILL BECOME CENTERED OVER THE REGION. TEMPS WILL DROP INTO THE TEENS AS THE REGION RADIATES OVERNIGHT UNDER CALM AND CLEAR CONDITIONS. A QUICK TRANSITION WILL OCCUR THURSDAY MORNING AS THE SFC HIGH MOVES OFF THE COAST AND SOUTHERLY FLOW MOVES INTO THE REGION AHEAD OF A COLD FRONT. WARM AIR ADVECTION WILL MOVE INTO THE REGION ALOFT WITH 850 TEMPS GOING POSITIVE THURSDAY. THE COLD FRONT ASSOCIATED WITH A GREAT LAKES CLIPPER WILL MOVE ACROSS THE OHIO VALLEY THURSDAY MORNING. THIS WILL ALLOW TEMPS ACROSS MOST OF THE MID-ATLANTIC TO RISE ABOVE FREEZING UNDER SOUTHERLY FLOW. DUE TO SNOWCOVER ACROSS THE NORTHERN PORTIONS OF THE OUTLOOK AREA...TEMPS NEAR THE MASON DIXON LINE SHOULD STAY COLDER AND BARELY REACH FREEZING THURSDAY AFTERNOON. TEMPS FURTHER SOUTH WILL REACH THE MID TO UPPER 30S. DISTURBANCES AHEAD OF THE COLD FRONT WILL LEAD TO PRECIPITATION TO MOVE ACROSS THE ALLEGHENY FRONT AND POTOMAC HIGHLANDS THURSDAY AFTERNOON. FCST SOUNDINGS DEPICT A GOOD AMT OF LOW LEVEL DRY AIR AS THE PRECIP MOVES INTO THE REGION. THIS SHOULD LEAD TO LIGHT PRECIPITATION TO START AS THE COLUMN WETBULBS. SNOW IS EXPECTED TO BEGIN ACROSS THE WESTERN SLOPES AND THE POTOMAC HIGHLANDS THURSDAY AFTERNOON. AS THE COLD FRONT MOVES INTO THE APPALACHIAN REGION...LIGHT PRECIP WILL MOVE EASTWARD AND SPREAD ACROSS MOST OF THE MID-ATLANTIC STAYING SNOW NEAR THE MASON DIXON LINE AND RAIN/SNOW FURTHER SOUTH WHERE TEMPS WILL BE WARMER. ALL RAIN IS EXPECTED SOUTH OF DC INCLUDING THE PIEDMONT...CENTRAL FOOTHILLS AND SOUTHERN MD BEFORE CHANGING TO RAIN/SNOW AS THE WAVE OF PRECIP MOVES EASTWARD. NOTE FOR AREAS NEAR FREEZING ACROSS THE MASON DIXON LINE...SATURATION SHOULD LEAD TO A BELOW FREEZING COLUMN BUT WAA ALOFT MAY LEAD TO SLEET MIXING IN. ACCUMULATIONS WILL BE LIGHT RANGING FROM 2-3 INCHES ACROSS THE WESTERN SLOPES TO 1-2 INCHES POSSIBLE ACROSS WESTERN MARYLAND. LESS THAN AN INCH IS EXPECTED FURTHER SOUTH. HIGHER AMOUNTS ACROSS THE WESTERN SLOPES ARE POSSIBLE AND AN ADVISORY MAY BE IN THE FUTURE FOR THIS AREA. ENERGY FROM AN AMPLIFYING UPPER LEVEL TROUGH BEHIND THE COLD FRONT MAY LEAD TO FLURRIES ACROSS THE REGION INTO FRIDAY. && .LONG TERM /FRIDAY THROUGH TUESDAY/... BOTH THE 12Z GFS AND 12Z ECMWF HAS A NEG TILT H5 TROUGH MOVING ACROSS SOUTHERN NEW ENGLAND FRIDAY NIGHT. THIS TAPS VERY COLD H85 TEMPS AOB -14 ACROSS THE ENTIRE CWA FRIDAY NIGHT...BRINGING SINGLE DIGITS WEST OF THE BLUE RIDGE AND THE TEENS TO THE METRO AREAS FOR FRIDAY NIGHT LOWS. WINDS WILL CONTINUE STRONG ON FRIDAY NIGHT ALONG WITH LOW MIN TEMPS LIKELY PRODUCING ADVISORY LEVEL WIND CHILLS AT LEAST WEST OF THE BLUE RIDGE ALONG WITH UPSLOPE SNOW SHOWERS. SAT AND SAT NIGHT SEE H5 HGHT RISES AND A BIT OF MODERATING TEMPS...AS SUNDAY HAS A DEEPENING LOW APPROACHING THE CWA FROM THE TN VALLEY. THE 12Z ECMWF IS A BIT SLOWER BY 6 HOURS...BUT BOTH MODELS HAVE THE SAME IDEA. WITH COLD TEMPS IN PLACE...THIS WILL BRING RAIN OR SNOW LIKELY SUNDAY AFTERNOON AND NIGHT. MONDAY WILL SEE A REINFORCING SHOT OF COLDER AIR WITH 12Z ECMWF TEMPS ONCE AGAIN REACHING AOB -14C BY TUESDAY MORNING...ALONG WITH ANOTHER GOOD CHC OF UPSLOPE SNOW SHOWERS. PER THE EXTENDED MEX GUIDANCE THROUGH THE LONG TERM...TEMPS WILL BE GENERALLY BELOW NORMAL...WITH SATURDAY AND TUESDAY APPEARING TO BE THE COLDEST WITH BOTH MAX AND MIN TEMPS ABOUT 10 DEG BELOW NORMAL. SATURDAY HAS THE LEAST CHANCE OF PCPN...AND MON NIGHT/TUE HAVING THE GREATEST CHC OF PCPN. && .AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
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A BAND OF CLOUDS WHICH EXTENDS ACROSS CENTRAL VA AND CENTRAL MD IS GRADUALLY THINNING OUT THIS EVENING. SOME MID AND HIGH CLOUDS MAY LINGER TONIGHT...BUT OTHERWISE VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD AND INTO WEDNESDAY NIGHT. NW WIND GUSTS AOA 20 KT WILL REMAIN POSSIBLE THROUGH WEDNESDAY WITH THE EXCEPTION OF CHO...ALTHOUGH SOME LULLS IN THE GUSTS MAY OCCUR AT TIMES TONIGHT. THESE WINDS WILL DIMINISH WEDNESDAY EVENING. MVFR/IFR CONDITIONS ARE POSSIBLE THURSDAY AFTERNOON AND EVENING AS A COLD FRONT CROSSES THE TERMINALS. RA/SN IS EXPECTED WHICH MAY REDUCE VSBYS INTO THURSDAY EVENING. STRONG NORTHWEST WIND GUSTS CONTINUES ON FRIDAY NIGHT WITH VFR. MVFR CONDITIONS RETURN TO THE TERMINALS LATE SUNDAY FOLLOWED BY ANOTHER BLAST OF NORTHWEST WINDS MONDAY AND MONDAY NIGHT.
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&& .MARINE...
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SOLID SCA CONDITIONS IN NW FLOW CONTINUE ACROSS THE WATERS THIS EVENING AND WILL REMAIN THROUGH TONIGHT. THE PERIOD OF BREEZY CONDITIONS IS EXPECTED TO EXTEND THROUGH WEDNESDAY AS WELL. WINDS WILL BEGIN TO DIMINISH WEDNESDAY EVENING AS HIGH PRESSURE BUILDS IN...BUT HAVE EXTENDED THE SCA WITH THE EXCEPTION OF THE UPPER TIDAL POTOMAC...AS IT WILL LIKELY TAKE TIME FOR THE GUSTS TO COMPLETELY SUBSIDE. SOUTHERLY FLOW WILL INCREASE ACROSS THE WATERS THURSDAY AND THURSDAY EVENING AND SCA WILL BE POSSIBLE. A COLD FRONT WILL CROSS THE WATERS BY FRIDAY MORNING AND NW WINDS WILL INCREASE TO S 20-30 KTS WITH GUSTS UP TO 45 KTS ON THE WATERS. GALES WILL BE LIKELY FRIDAY. IN THE LONG TERM...GALES WILL LIKELY CONTINUE FRIDAY NIGHT...THEN RETURN AGAIN ON MONDAY AND MONDAY NIGHT.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...WINTER WEATHER ADVISORY UNTIL 1 AM EST WEDNESDAY FOR MDZ501. VA...NONE. WV...WINTER WEATHER ADVISORY UNTIL 1 AM EST WEDNESDAY FOR WVZ501- 503-505. MARINE...SMALL CRAFT ADVISORY UNTIL MIDNIGHT EST WEDNESDAY NIGHT FOR ANZ530>534-537>543. SMALL CRAFT ADVISORY UNTIL 6 PM EST WEDNESDAY FOR ANZ535-536.
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&& $$ SYNOPSIS...LEE/GMS NEAR TERM...ADS/GMS SHORT TERM...HAS LONG TERM...LEE AVIATION...ADS/LEE/HAS MARINE...ADS/LEE/HAS

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