Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 250253 AAB AFDLWX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 953 PM EST MON NOV 24 2014 .SYNOPSIS... LOW PRESSURE INTENSIFYING OVER THE GREAT LAKES WILL BRING AN ASSOCIATED COLD FRONT THROUGH THE MID-ATLANTIC LATE THIS AFTERNOON AND EARLY THIS EVENING. LOW PRESSURE IS EXPECTED TO TRACK NORTH ALONG THE COAST WEDNESDAY. HIGH PRESSURE WILL RETURN FOR THURSDAY AND FRIDAY. && .NEAR TERM /THROUGH TUESDAY/...
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WHILE THE SRN TIP OF A DISSIPATING COLD FRONT SKIMS THE NRN EDGE OF THE AREA THIS EVE...AN EXPRESS LANE OF MOISTURE SETS UP ALONG THE SRN ATLC STATES. THE NRN PERIPHERY OF THIS FEATURE JUST GLANCING SRN MD AND THE LOWER MD BAY. ONLY A ISOLATED SHOWER OR TWO OVER THE NEXT FEW HRS. THOUGH THE AREA HAS CLEARED OUT DATING BACK INTO THE EARLY AFTN HRS TODAY...CIRRUS DEBRIS FROM THIS SRN ACTIVITY IS BEGINNING TO SPREAD NWD AS WELL. THIS WILL ESSENTIALLY KEEP TEMPS MODERATED A DEGREE OR TWO HEADING INTO THE LATE NIGHT HRS. AFTER NEAR-RECORD WARMTH TODAY...AND HIGH DEWPOINTS TO MATCH... THE TAIL OF THE COLD FRONT WILL USHER-IN SOME DRIER AIR FROM WEST TO EAST OVERNIGHT. THE MORE HUMID AIR ACROSS THE REGION WILL BE GRADUALLY REPLACED W/ COOLER-DRIER AIR INTO THE PREDAWN HRS TMRW. THE TIMING DIFFERENCE BETWEEN WHEN THE COOL/DRY AIR ARRIVES AND OUR TYPICAL LOW TEMPS OCCUR WILL ACTUALLY CREATE QUITE A DIFFERENCE IN LOWS OVER THE REGION. THE HIGHER TERRAIN WILL SEE TEMPS DROP WELL INTO THE 30S...AS WILL NEARBY VALLEYS - WHILE AREAS ALONG AND E OF THE BLUE RIDGE WILL STAY MORE MODERATED IN THE M-U40S AND EVEN M50S CLOSER TO THE BAY. PREV DISC... TUESDAY...DRY WITH HIGH PRESSURE NOSING IN FROM THE LOWER MISSISSIPPI VALLEY. INCREASING MID AND HIGH LEVEL CLOUDS THROUGH THE DAY AS THE FRONT REMAINS JUST OFFSHORE AND THE LOW PRESSURE SYSTEM BEGINS TO TAKE SHAPE OVER NORTHERN FL. DESPITE BEING MUCH COOLER THAN TODAY... THE COLDEST AIR STAYS POISED OVER THE GREAT LAKES AND HIGHS WILL BE NEAR CLIMO IN THE 50S. SHADED SOUTHEAST CWA A LITTLE COOLER DUE TO THE INCREASING CLOUDS.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... A POTENT JETMAX/SHORTWAVE WILL TRACK THROUGH THE GULF COAST STATES TUESDAY NIGHT AND THIS WILL CAUSE COASTAL LOW PRESSURE TO DEVELOP OFF THE SOUTHEAST COAST. AT THE SAME TIME...HIGH PRESSURE WILL BUILD TO OUR NORTH ALLOWING FOR COLDER AND DRIER AIR TO FILTER INTO THE REGION. HIGH AND MID-LEVEL CLOUDS WILL INCREASE AHEAD OF THIS SYSTEM TUESDAY NIGHT...BUT MUCH OF THE TIME WILL TURN OUT DRY WITH THE SYSTEM REMAINING TO OUR SOUTH AND WEST. HOWEVER...PRECIPITATION IS EXPECTED TO OVERSPREAD THE AREA QUICKLY EARLY WEDNESDAY MORNING AS THE COASTAL LOW TRACKS NORTHEAST TOWARD CAPE HATTERAS. THE LOW WILL INTENSIFY AS IT TRACKS NORTHEAST...AND THIS WILL ALLOW FOR MOISTURE FROM THE ATLANTIC AND GULF OF MEXICO TO GET WRAPPED INTO THE STORM. THEREFORE...PRECIPITATION WILL BE MODERATE TO LOCALLY HEAVY AT TIMES DURING THE DAY WEDNESDAY. THE MAIN QUESTION IS HOW MUCH COLD AIR WILL WORK ITS WAY INTO THE REGION...CAUSING THE THREAT FOR SNOW. AS OF NOW...IT APPEARS THAT THERE WILL BE ENOUGH COOLING FROM THE WET-BULB EFFECT AND DYNAMICAL COOLING FOR ANY RAIN OR MIXED PRECIPITATION TO QUICKLY CHANGE TO SNOW FOR LOCATIONS NEAR THE MASON-DIXON LINE AND ALSO NEAR AND WEST OF THE BLUE RIDGE MOUNTAINS. THE HEAVIEST SNOW ACCUMULATION IS MOST LIKELY TO FALL IN THE MOUNTAINS...BUT THERE IS A POTENTIAL FOR SEVERAL INCHES OF SNOW ACROSS MOST OF THESE AREAS SO A WATCH HAS BEEN ISSUED. FOR LOCATIONS CLOSER TO INTERSTATE 95...THERE MAY BE ENOUGH WARM AIR FOR PRECIPITATION TO START OUT AS RAIN...BUT EVEN ACROSS THESE AREAS PRECIPITATION WILL LIKELY CHANGE TO SNOW DUE TO THE COOLING AFFECTS PREVIOUSLY MENTIONED. HOWEVER...SURFACE TEMPS WILL HOVER CLOSE TO OR PERHAPS EVEN A COUPLE DEGREES ABOVE FREEZING AND THIS MAY MAKE IT DIFFICULT FOR SNOW TO STICK. THE HIGHEST DEGREE OF UNCERTAINTY IS IN THESE AREAS SO PLEASE STAY TUNED TO THE LATEST FORECASTS FOR UPDATES. FOR LOCATIONS SOUTH AND EAST OF I-95...MOSTLY RAIN IS EXPECTED...BUT THERE IS A POTENTIAL FOR SNOW TO MIX IN WEDNESDAY AFTERNOON. PRECIPITATION WILL END FROM SOUTHWEST TO NORTHEAST LATER WEDNESDAY AFTERNOON INTO WEDNESDAY EVENING. EXACT TIMING IS STILL UNCERTAIN BUT THE FORECAST LEANS A BIT TOWARD THE MORE PROGRESSIVE GUIDANCE SINCE THIS SHOULD BE A FAST MOVING SYSTEM AND IT IS NOT EXPECTED TO PHASE WITH THE NORTHERN BRANCH UNTIL AFTER IT IS OFF TO OUR NORTH. TEMPS WILL DIP BELOW FREEZING WEDNESDAY NIGHT AS CONDITIONS DRY OUT. THEREFORE...ANY WET OR SLUSHY ROADS MAY FREEZE UP. && .LONG TERM /THURSDAY THROUGH MONDAY/... LOW PRESSURE DEPARTS INTO THE CANADIAN MARITIMES THURSDAY. MEANWHILE...500 MB NORTHERN STREAM TROUGH MOVES ACROSS THE AREA. SNOW SHOWERS POSSIBLE OVER THE WESTERN RIDGES BUT TRAJECTORIES NOT FAVORABLE FOR PROLONGED UPSLOPE. CANNOT RULE OUT A FEW FLURRIES EAST OF THE RIDGES AS THE TROUGH AXIS PASSES BUT MOSTLY JUST EXPECTING PASSING CLOUDS IN A BREEZY WEST FLOW. HIGHS SHOULD MAKE IT TO AROUND 40 DEGREES THURSDAY AFTERNOON. COLDER TEMPS AT 850 MB ACCOMPANY THE NORTHERN STREAM WAVE...SO BELOW NORMAL TEMPS ARE EXPECTED LATER THIS WEEK. SURFACE HIGH PRESSURE MOVES ACROSS FRIDAY INTO FRIDAY NIGHT...THEN MOVES OFFSHORE FOR THE WEEKEND ACCOMPANIED BY A GRADUAL WARMUP TO NEAR NORMAL TEMPERATURES. A FRONT MAY APPROACH THE AREA BY THE BEGINNING OF NEXT WEEK. && .AVIATION /01Z TUESDAY THROUGH SATURDAY/...
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VFR CONDITIONS ARE EXPECTED THROUGH THE TAF PERIOD. WINDS HAVE DIMINISHED A TIER - DOWN INTO THE SUSTAINED 10-15KT RANGE OR SLIGHTLY LOWER. A COLD FRONTAL WILL EVENTUALLY CHANGE SFC WIND DIRECTIONS TO MORE WLY/NWLY INTO THE PREDAWN HRS TMRW AND REMAIN AROUND 10KT OR LESS THROUGH TUESDAY. VFR CONDITIONS ARE EXPECTED TUESDAY NIGHT. A RAIN AND SNOW MIX WILL OVERSPREAD THE TERMINALS EARLY WEDNESDAY MORNING. PRECIPITATION WILL CHANGE TO ALL SNOW WEDNESDAY AND IFR CONDITIONS ARE EXPECTED. THE LOW WILL MOVE AWAY FROM THE AREA WEDNESDAY NIGHT AND CONDITIONS WILL IMPROVE TO VFR LEVELS. GUSTY NORTH-NORTHWEST WINDS ARE POSSIBLE WEDNESDAY INTO EARLY WEDNESDAY EVENING. MAINLY VFR EXPECTED THU-THU NIGHT W/ W WIND 10-15 KTS. VFR INTO NEXT WEEKEND...WINDS BECOME LIGHT/VARIABLE AS HIGH PRESSURE MOVES OVERHEAD FRI-FRI NIGHT...THEN S AROUND 10 KTS SAT.
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&& .MARINE...
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GUSTY SLY WINDS HANGING ON OVER THE MUCH OF THE MID-LOWER BAY AND LOWER TP RVR. A COLD FRONT PASSAGE THEN GRADUALLY DIMINISH WHILE BECOMING WESTERLY. NOT A STRONG SURGE OF COLD AIR...SO GUSTS SHOULD TAPER OFF DESPITE THE FRONTAL PASSAGE...W/ SCA CONDS ENDING INTO THE OVERNIGHT HRS. WESTERLY WINDS THROUGH THE DAY TUESDAY AT LESS THAN 15KT. LOW PRESSURE WILL DEVELOP OFF THE SOUTHEAST COAST TUESDAY NIGHT. A SMALL CRAFT ADVISORY IS IN EFFECT LATE TUESDAY NIGHT FOR THE MARYLAND CHESAPEAKE BAY FROM SANDY POINT TO SMITH POINT AND FOR THE LOWER TIDAL POTOMAC RIVER FROM COBB ISLAND TO SMITH POINT. THE LOW WILL MOVE UP THE MID-ATLANTIC COAST WEDNESDAY AND IT WILL INTENSIFY AS IT MOVES OFF TO OUR NORTHEAST WEDNESDAY NIGHT. A SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED FOR THE WATERS WEDNESDAY INTO WEDNESDAY EVENING. A GALE WARNING MAY BE NEEDED FOR PORTIONS OF THE WATERS WEDNESDAY. GUSTY WEST WINDS BETWEEN DEPARTING/DEEPENING LOW PRESSURE AND APPROACHING HIGH PRESSURE WILL LIKELY BREACH SMALL CRAFT ADVISORY CRITERIA THURSDAY NIGHT INTO FRIDAY. WINDS WILL LIGHTEN AS HIGH PRESSURE MOVES OVERHEAD FRIDAY AFTERNOON AND NIGHT...THEN SOUTHERLY CHANNELING LOOKS TO BRING A RETURN TO HIGHER GUSTS SATURDAY AFTERNOON.
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&& .TIDES/COASTAL FLOODING...
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CONTINUED SOUTHERLY FLOW HAS KEPT HIGHER TIDAL ANOMALIES IN PLACE BUT W/ A RELATIVELY LIGHTER FLOW IN RECENT HRS...THE DEPARTURES ARE BEGINNING TO DECREASE A BIT. ASTRONOMICAL NORMS ARE RELATIVELY LOW...THEREFORE MINOR COASTAL FLOODING IS NOT EXPECTED WITH THE HIGH TIDE CYCLE THIS EVENING. ANOMALIES WILL DECREASE BEHIND A COLD FRONT LATER TONIGHT.
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&& .CLIMATE...
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HIGH TEMPERATURES TODAY FOR DCA/IAD/BWI WERE NEAR RECORDS LEVELS. HERE ARE THE RECORD HIGHS AND THE YEAR THEY OCCURRED... DCA...74 IN 1958. ..OFFICIALLY TIED.. IAD...74 IN 1979. ..REACHED 70.. BWI...73 IN 1979. ..REACHED 72..
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...WINTER STORM WATCH FROM WEDNESDAY MORNING THROUGH WEDNESDAY AFTERNOON FOR MDZ003>007-501-502. VA...WINTER STORM WATCH FROM WEDNESDAY MORNING THROUGH WEDNESDAY AFTERNOON FOR VAZ025>031-036>040-042-501-503-504. WV...WINTER STORM WATCH FROM WEDNESDAY MORNING THROUGH WEDNESDAY AFTERNOON FOR WVZ050>053-055-501>506. MARINE...SMALL CRAFT ADVISORY UNTIL 1 AM EST TUESDAY FOR ANZ532>534-537- 540>543. SMALL CRAFT ADVISORY FROM 1 AM TO 6 AM EST WEDNESDAY FOR ANZ532>534-537-540>543. && $$ UPDATE...GMS PREV DISCUSSION...ADS/BJL/DFH

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