Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 232032 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 332 PM EST FRI JAN 23 2015 .SYNOPSIS... LOW PRESSURE OVER THE SOUTHEASTERN STATES WILL TRACK NORTHEAST TO A POSITION EAST OF THE DELMARVA SATURDAY MORNING AND MOVE INTO THE GULF OF MAINE SATURDAY NIGHT. HIGH PRESSURE WILL BRIEFLY RETURN TO THE AREA BEFORE A FAST MOVING LOW PRESSURE SYSTEM WILL CROSS THE AREA FROM THE WEST SUNDAY NIGHT THROUGH MONDAY. HIGH PRESSURE IS THEN EXPECTED THROUGH THE MIDWEEK. && .NEAR TERM /THROUGH SATURDAY/... HIGH PRESSURE WAS LOCATED ALONG THE MID-ATLANTIC COAST THIS AFTERNOON...WHILE LOW PRESSURE HAS FORMED ALONG THE NORTHEAST GULF COAST. OVERRUNNING HAS ALREADY WORKED NORTHWARD INTO THE SOUTHWEST PORTION OF THE CWA EARLY THIS AFTERNOON. SNOW HAS BEEN REPORTED IN THE CENTRAL SHENANDOAH VALLEY...WITH RAIN IN THE FOOTHILLS. PRECIPITATION WILL CONTINUE TO SPREAD TO THE NORTH THROUGH THIS EVENING...WITH WIDESPREAD PRECIPITATION OVERNIGHT. THERMAL PROFILES/TEMPERATURES ARE CHALLENGING WITH THIS EVENT...AND WILL ULTIMATELY DETERMINE HOW MUCH SNOW/ICE OCCURS. HAVE LEANED TOWARD A COLDER SOLUTION FOR THIS EVENT PARTICULARLY IN THE NORTHWEST CORNER OF THE CWA...SIDING MORE WITH 09Z SREFS/12Z NAM. WILL RUN THE GAMUT OF P-TYPES ACROSS THE CWA WITH NORTHWEST CORNER MAINLY AS SNOW POSSIBLY MIXING WITH A LITTLE SLEET/FREEZING RAIN. SOUTHEAST OF HERE A TIGHT GRADIENT OF SNOW WILL BE ENCOUNTERED AND THERE IS SOME UNCERTAINTY WHERE THIS SETS UP. ADVISORY LEVEL SNOWS ARE LIKELY FROM NORTHEAST MARYLAND SOUTHWESTWARD INTO THE SHENANDOAH VALLEY. SNOW AMOUNTS LIKELY DROP OFF QUITE A BIT SOUTHEAST OF THIS LINE...WITH THE REASONING BEHIND THE ADVISORY IN THIS AREA FROM A BRIEF PERIOD OF FREEZING RAIN OVERNIGHT. AT THIS TIME...SOUTHERN MARYLAND APPEARS TO BE PRIMARILY RAIN FOR THE EVENT. MAIN THRUST OF PRECIPITATION LIKELY MOVES OUT EARLY SATURDAY MORNING AS THE COASTAL STORM MOVES NORTH OF OUR LATITUDE BUT THERE MAY BE A LAST BAND OF PRECIPITATION AS THE VORT MOVES THROUGH THEREAFTER AND AT THAT TIME 850 MB TEMPERATURES WILL LOWER FROM WEST TO EAST. SO PLACES WITH A MIX OR RAIN MAY WIND UP ENDING AS SNOW SATURDAY. && .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 UPSLOPING 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 FRONTOGENETICAL 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 /20Z FRIDAY THROUGH WEDNESDAY/... CHALLENGING AVIATION FORECAST TODAY DUE TO DIFFERENT P-TYPES WITH THE UPCOMING EVENT TONIGHT/SATURDAY. AT THE HUBS...ONSET MAY BE MAINLY RAIN BUT LIKELY WOULD TRANSITION TO A PERIOD OF FREEZING RAIN/SNOW OVERNIGHT. CONFIDENCE OF WINTRY PRECIP IS LOWEST AT DCA...AS MAINLY RAIN COULD OCCUR DURING THE BULK OF THE EVENT. DESPITE P-TYPE...IFR IS LIKELY TO DEVELOP AT ALL TERMINALS PER SREFS POSSIBLY LIFR IAD/MRB. THE BULK OF THE PRECIPITATION MOVES OUT SATURDAY MORNING...CIGS WILL GRADUALLY IMPROVE THROUGH AFTERNOON. 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 KTS 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. && .MARINE... SOUTHEAST WINDS ARE IN PLACE OVER THE WATERS NOW...BUT 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 A PORTION OF THE WATERS AND THEN ALL WATERS ON SATURDAY WITH 20 KT GUSTS LIKELY. LINGERING SCA GUSTS UP TO 20 KTS SAT EVENING...THEN DECREASING OVERNIGHT. WINDS REMAIN MAINLY BELOW SCA CRITERIA SUNDAY...WITH LOW CHC OF OCNL GUSTS TO 18 KTS 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. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...WINTER WEATHER ADVISORY UNTIL NOON EST SATURDAY FOR DCZ001. MD...WINTER STORM WARNING UNTIL NOON EST SATURDAY FOR MDZ003. WINTER WEATHER ADVISORY UNTIL NOON EST SATURDAY FOR MDZ004>006- 011-013-014-503>508. WINTER STORM WARNING UNTIL NOON EST SATURDAY FOR MDZ501-502. VA...WINTER WEATHER ADVISORY UNTIL 10 AM EST SATURDAY FOR VAZ025- 026-036-037-503-504-508. WINTER WEATHER ADVISORY UNTIL NOON EST SATURDAY FOR VAZ027- 029>031-038>040-050-051-501-502-507. WINTER WEATHER ADVISORY UNTIL NOON EST SATURDAY FOR VAZ052>054- 505-506. WINTER STORM WARNING UNTIL NOON EST SATURDAY FOR VAZ028. WV...WINTER WEATHER ADVISORY UNTIL 10 AM EST SATURDAY FOR WVZ505- 506. WINTER STORM WARNING UNTIL NOON EST SATURDAY FOR WVZ051-052. WINTER WEATHER ADVISORY UNTIL NOON EST SATURDAY FOR WVZ053. WINTER STORM WARNING UNTIL NOON EST SATURDAY FOR WVZ050-055- 501>504. 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. && $$ SYNOPSIS...BPP NEAR TERM...BPP SHORT TERM...SEARS LONG TERM...KLW AVIATION...BPP/SEARS/KLW MARINE...BPP/SEARS/KLW

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