Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 240255 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 955 PM EST FRI JAN 23 2015 .SYNOPSIS...
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LOW PRESSURE OVER GEORGIA WILL DEVELOP AND TRACK NORTHEAST ACROSS THE CAROLINAS TONIGHT AND JUST OFF THE DELMARVA COAST SATURDAY MORNING...REACHING THE GULF OF MAINE SATURDAY EVENING. THE NEXT LOW PRESSURE SYSTEM WILL CROSS THE AREA FROM THE WEST SUNDAY NIGHT THROUGH MONDAY. HIGH PRESSURE IS THEN EXPECTED THROUGH THE MIDWEEK.
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&& .NEAR TERM /THROUGH SATURDAY/...
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AS OF 02Z...1008MB SFC LOW OVER AL/GA BORDER. SURGE OF WARM AIR ALOFT HAS TURNED MOST SNOW OVER TO RAIN...MODERATE AT TIMES. POCKETS OF FREEZING RAIN WITH SUB 32F MESONET REPORTS NORTH AND WEST OF DC. SNOW STILL REPORTED AT CUMBERLAND WHICH LOOKS TO BE THE BEST BET FOR SNOWFALL APPROACHING WARNING TOTALS. FREEZING RAIN IN THE SOUTHERN POTOMAC HIGHLANDS WARRANTED RAISING A WARNING FOR PENDLETON AND HIGHLAND COUNTIES. COLD AIR FINALLY COMES IN LATE TONIGHT FROM THE NW AS THE LOW LEVEL LOW SHIFTS EAST OF THE AREA/OFF THE MOUTH OF THE DELMARVA. HOWEVER...PRECIP CUTS OFF PRETTY QUICKLY. WILL MAINTAIN HEADLINES AS OF NOW DUE TO FREEZING RAIN THREAT. WRAP AROUND PRECIP HAS THE BEST SHOT AT ACCUMULATING AROUND MIDDAY AS THE UPR TROUGH SWINGS THROUGH THE AREA. SINCE IT IS DURING DAYLIGHT HOURS...EXPECT LESS THAN AN INCH OF SNOW. PERHAPS IT WILL BE SIMILAR TO SNOW AT THE ONSET AND AMOUNT TO A COUPLE TENTHS (0.2IN AT LWX). DOWNSLOPING NWLY FLOW AFTER THE UPR TROUGH PASSES WITH GUSTS 20 TO 25 MPH AND MOST PLACES GETTING SUNSHINE BEFORE SUNSET.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... PCPN TAPERING OFF BY SAT EVENING AS SFC LOW PUSHES OFF TO THE NORTHEAST AND THE MAIN FORCING WITH THE UPPER LVL SHORTWAVE SHIFTS EAST. WILL MAINTAIN UPSLOPE SNOW SHOWERS OVER THE ALLEGHENY FRONT REGION WITH A WNW FLOW ON THE BACKSIDE OF THE LOW. THE SHOWERS ARE EXPECTED TO TAPER OFF AS THE WINDS BACK TO THE SW NEAR DAYBREAK SUN MORNING...BUT THE LACK OF PCPN WILL BE SHORT LIVED AS AN ALBERTA CLIPPER QUICKLY APPROACHES THE REGION. TEMPS SAT NIGHT NEAR NORMAL...WITH EVERYWHERE IN THE UPPER 20S TO RIGHT AROUND 30. WITH THE PASSING OF THE COASTAL LOW TONIGHT-TOMORROW...ATTENTION WILL THEN TURN TO THE APPROACHING CLIPPER FOR SUN NIGHT-MON WHICH IS EXPECTED TO BRING ACCUMULATING SNOW TO MOST OF THE MID ATLANTIC MAINLY LATE SUN EVENING THRU MON MORNING. STILL SOME UNCERTAINTY ON TOTALS BUT ADVISORY LEVEL SNOW IS VERY POSSIBLE. MODELS HAVE BEEN CONSISTENT WITH THIS SYSTEM PASSING THROUGH THE REGION SUN NIGHT...PUSHING OFFSHORE BY MON MORNING. BECAUSE OF THE CONSISTENCY HAVE GONE AHEAD AND INCREASED POPS TO CATEGORICAL ALONG THE MASON DIXON SOUTH INTO NORTHERN VA FOR THE SECOND HALF OF SUN NIGHT. CONFIDENCE ALSO EXISTS IN THE MAJORITY OF THE PCPN FALLING AS SNOW...WITH ONLY A PSBL RAIN/SNOW MIX AT THE ONSET. 850MB TEMPS INITIALLY AROUND -1 DEGREES...BUT DIPS DOWN TO AROUND -7 DEGREES CELSIUS OVERNIGHT SUNDAY...AND KEEPS DECREASING HEADING INTO MONDAY. WHILE THE CONFIDENCE EXISTS PCPN WILL OCCUR...THE QUESTION REMAINS HOW MUCH QPF/WHERE WILL THE AXIS OF HEAVIEST PCPN SETS UP. THE 12Z NAM IS THE OVERZEALOUS SOLUTION...BRINGING IN HIGHER AMTS FOR LONGER PERIOD OF TIME...WHILE THE 12Z GFS AND ECMWF HOLD BACK AND PLACE THE HIGHEST AMTS OVER NORTHERN VA BETWEEN 06-12Z. LOOKING ALOFT...THE DIGGING SHORTWAVE EXTENDS THE BETTER FORCING/ENERGY FURTHER SOUTH ON THE GFS/ECMWF WHILE THE NAM IS SHALLOWER AND BRINGS THE BEST FORCING ACROSS OUR AREA. OF NOTE...BOTH THE NAM AND ECMWF INDICATE THE BETTER FRONTOGENETIC FORCING INITIALLY EXTENDING PARALLEL TO THE OUR WESTERN HIGHER ELEVATIONS...THEN PIVOTING AND ALIGNING MORE FROM A CENTRAL MD SE TO SOUTHERN MD. AS SUCH...HAVE HIGHEST SNOW TOTALS 00-06Z OUR WESTERN AREA...THEN PIVOTED THE AREA OF HIGHEST SNOW FOR 06-12Z BRINGING IT DOWN THROUGH CENTRAL MD AND INTO THE DC/BALTIMORE METRO AREAS. WHILE THE EXPECTATION IS THAT EVERYONE WILL SEE SNOW WITH THIS SYSTEM...THINKING THERE WILL ACTUALLY BE PORTIONS OF THE PIEDMONT WHO SEE LESS SNOW THAN AREAS TO THE EAST AND WEST. FOR TOTALS...HAVE SIDED WITH THE LOWER/MORE CONSERVATIVE GFS/ECMWF QPF AMTS AND WITH MUCH COLDER TEMPS MOVING IN USED A 12:1 SNOW RATIO. THE HEAVIEST PCPN TAPERS OFF BY LATE MON MORNING AS THE CLIPPER QUICKLY PUSHES EAST AND THEN NORTH. ENDING TIME COULD BE OFF...NAM WANTS TO SEND IN DRIER AIR QUICKER ALOFT AND AS A RESULT...ENDING THE EVENT WITH BRIEF PERIOD OF FZDZ. THE GFS STAYS SATURATED LONGER AND WOULD SUGGEST ENDING WITH LIGHT RAIN FOR MOST OF THE AREA. THINKING THERE WILL ACTUALLY BE A BREAK MONDAY AFTN THEN THE NEXT ROUND OF PCPN ON THE BACKSIDE OF THE LOW WITH A STRONG SHORTWAVE ROUNDING THE BASE OF THE PERSISTING UPPER LEVEL TROUGH. AS PREVIOUSLY MENTIONED...COLD 850MB TEMPS BEING MOVING IN SUNDAY...WITH SUN NIGHT LOWS UPPER 20S TO NEAR FREEZING EVERYWHERE. TEMPS WILL WARM BRIEFLY AND ONLY A COUPLE OF DEGREES MON MORNING...THEN DECREASE THROUGH THE AFTN. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... ANOTHER PIECE OF UPPER LEVEL ENERGY WILL DROP IN BEHIND THE DEPARTING ALBERTA CLIPPER LOW MONDAY NIGHT TO LEAVE A CHANCE FOR ADDITIONAL LIGHT SNOW OR SNOW SHOWERS MONDAY NIGHT INTO TUESDAY. ONCE THE MAIN TROUGH AXIS PIVOTS TO THE EAST...SOME UPSLOPE SNOW SHOWERS MAY STILL LINGER IN THE POTOMAC HIGHLANDS WHILE ELSEWHERE DRIES OUT. BUILDING HIGH PRESSURE WILL ENSURE DRY CONDITIONS TUESDAY NIGHT THROUGH WEDNESDAY NIGHT EXCEPT FOR SOME UPSLOPE SNOW SHOWERS IN THE POTOMAC HIGHLANDS. IT WILL BE COLDER AS WELL. HIGH PRESSURE WILL MOVE EAST THURSDAY TO ALLOW FOR A GREAT LAKES LOW PRESSURE SYSTEM TO DRAG A COLD FRONT ACROSS THE REGION LATE THURSDAY AND THURSDAY NIGHT. THERE IS A SLIGHT CHANCE OF SNOW SHOWERS LATE THURSDAY AND THURSDAY NIGHT. A CHANCE OF UPSLOPE SNOW SHOWERS IN THE POTOMAC HIGHLANDS FRIDAY AS HIGH PRESSURE BUILDS EAST BEHIND THE COLD FRONT. ELSEWHERE SHOULD BE CHILLY AND DRY. && .AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
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RAIN CONTINUES FOR TAF SITES INTO THE OVERNIGHT...SNOW MOVES BACK IN LATE FROM THE WEST. IFR CONDS CONTINUE WELL INTO SATURDAY. THE BULK OF THE PRECIPITATION MOVES OUT SATURDAY MORNING...CIGS WILL GRADUALLY IMPROVE THROUGH AFTERNOON WITH NWLY FLOW GUSTING 20 TO 25 KT. VFR CONDITIONS SAT NIGHT THROUGH AT LEAST SUN AFTN. SUB-VFR CONDITIONS LIKELY BY SUN EVENING WITH PCPN MOVING IN FROM THE WEST WITH PSBL IFR IN THE EVENING...AND MORE LIKELY AFTR 06Z. BRIEF PERIOD OF RAIN/SNOW SUN EVENING BCMG ALL SNOW 03-06Z AND REMAINING ALL SNOW REMAINDER OF THE NIGHT. DIMINISHED CONDITIONS THRU MON MORNING...SLOWLY IMPROVING MON AFTN. GUSTS UP TO 20 KT PSBL MONDAY. MVFR OR IFR CONDITIONS MAY LINGER MONDAY NIGHT INTO EARLY TUESDAY WITH LINGERING PERIODS OF LIGHT SNOW. VFR CONDITIONS MIDDAY TUESDAY AND TUESDAY AFTERNOON. WINDS WILL BE NORTH 10 TO 15 KNOTS GUSTING OVER 20 KNOTS MONDAY EVENING...THEN DIMINISHING MONDAY OVERNIGHT THROUGH TUESDAY.
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&& .MARINE...
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ELY FLOW AROUND 10 KT INTO THE OVERNIGHT. AS LOW PRESSURE APPROACHES THE COAST TONIGHT...WINDS ARE EXPECTED TO SHIFT TO THE NORTH THEN TO THE NORTHWEST SATURDAY. SCA WILL BE IN EFFECT AFTER MIDNIGHT FOR SRN PORTIONS OF THE WATERS AND THEN ALL WATERS ON SATURDAY WITH 20 TO 25 KT GUSTS EXPECTED. LINGERING SCA GUSTS UP TO 20 KT SAT EVENING...THEN DECREASING OVERNIGHT. WINDS REMAIN MAINLY BELOW SCA CRITERIA SUNDAY...WITH LOW CHC OF OCNL GUSTS TO 18 KT PSBL SUN AFTN. HIGHER CONFIDENCE OF GUSTS INTO THE 20S ON MONDAY WITH NORTHERLY FLOW SO SCA WILL MOST LIKELY BE NEEDED AFTER 12Z MON. SMALL CRAFT ADVISORY MAY BE NEEDED MONDAY EVENING AS NORTHERLY WINDS GUST OVER 20 KNOTS. NO MARINE HAZARDS MONDAY OVERNIGHT THROUGH TUESDAY.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...WINTER STORM WARNING UNTIL NOON EST SATURDAY FOR MDZ003-501- 502. WINTER WEATHER ADVISORY UNTIL NOON EST SATURDAY FOR MDZ004>006- 011-503>508. VA...WINTER STORM WARNING UNTIL NOON EST SATURDAY FOR VAZ028-503- 504. WINTER WEATHER ADVISORY UNTIL 10 AM EST SATURDAY FOR VAZ025- 026-036-037-508. WINTER WEATHER ADVISORY UNTIL NOON EST SATURDAY FOR VAZ027- 029>031-038>040-050>053-501-502-505>507. WV...WINTER STORM WARNING UNTIL NOON EST SATURDAY FOR WVZ050>052- 055-501>506. WINTER WEATHER ADVISORY UNTIL NOON EST SATURDAY FOR WVZ053. MARINE...SMALL CRAFT ADVISORY FROM 1 AM TO 6 PM EST SATURDAY FOR ANZ532>534-537-540>543. SMALL CRAFT ADVISORY FROM NOON TO 6 PM EST SATURDAY FOR ANZ530- 531-535-536-538-539.
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&& $$ SYNOPSIS...BAJ/BPP NEAR TERM...BAJ/BPP SHORT TERM...SEARS LONG TERM...KLW AVIATION...BAJ/SEARS/BPP/KLW MARINE...BAJ/SEARS/BPP/KLW

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