Area Forecast Discussion
Issued by NWS Sterling, VA

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621 FXUS61 KLWX 040817 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 317 AM EST THU FEB 4 2016 .SYNOPSIS...
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A COLD FRONT WILL STALL OFF THE MID-ATLANTIC COAST TODAY. A WAVE OF LOW PRESSURE WILL RIDE ALONG THE BOUNDARY...PASSING BY WELL TO OUR SOUTH AND EAST THURSDAY NIGHT INTO FRIDAY. HIGH PRESSURE WILL RETURN FOR SATURDAY. COASTAL LOW PRESSURE WILL PASS BY WELL TO OUR SOUTH AND EAST SUNDAY. ANOTHER LOW PRESSURE SYSTEM MAY IMPACT THE AREA EARLY NEXT WEEK.
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&& .NEAR TERM /THROUGH TODAY/...
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AS OF 315 AM THURSDAY...COLD FRONT CURRENTLY CROSSING OVER THE APPALACHIAN MOUNTAINS EARLY THIS MORNING AND WILL DELIVER GRADUALLY DRYING AND COOLING CONDITIONS. OUT AHEAD OF IT...STILL SEEING VERY MOIST LOW LEVELS WITH AREAS OF FOG...DRIZZLE...AND LOW CLOUDS. SHOULD SEE DISSIPATION OF THIS TOWARDS SUNRISE AS DRYING WORKS ITS WAY IN. OTHERWISE FRONT SETTLES SOUTH AND EAST OF THE REGION TODAY...LEAVING US WITH A MOSTLY DRY DAY ONCE THE FOG LIFTS...AT LEAST INTO THE FIRST HALF OF THE AFTERNOON...ALBEIT WITH A GOOD DEAL OF CLOUD COVER. AS NORTHWEST FLOW DEVELOPS...MAY SEE SOME LIGHT UPSLOPE SNOW SHOWERS ALONG THE ALLEGHENY FRONT...BUT NO ACCUMULATIONS EXPECTED. IN THE MID TO LATE AFTERNOON HOURS...AS WAVE OF LOW PRESSURE RIDES UP THE LINGERING FRONTAL BOUNDARY TO OUR SOUTH...WILL SEE RAIN SPREAD BACK NORTHWARD AND INTO PORTIONS OF OUR SOUTHEASTERN ZONES...ESPECIALLY SOUTHERN MARYLAND. HIGH TEMPERATURES WILL RANGE FROM THE MID/UPPER 30S WELL NORTH AND WEST TO LOW 50S SOUTH AND EAST.
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&& .SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/...
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WAVE LOW WILL MOVE FROM OFF THE COAST OF THE CAROLINAS THIS EVENING AND OUT TO SEA ON FRIDAY. EXPECTING STEADY RAIN TO BE FALLING FOR THE FIRST HALF OF TONIGHT...BUT AS TEMPERATURES COOL...ESPECIALLY IN ANY HEAVIER PRECIPITATION...WILL LIKELY SEE PRECIP MIX WITH AND CHANGE TO A PERIOD OF SNOW BEFORE ENDING FRIDAY MORNING. IS A MARGINAL SITUATION WITH BOUNDARY LAYER TEMPERATURES IN THE 33 TO 36 DEGREE RANGE...BUT COULD SEE A WET ACCUMULATION OF SNOW OF 0.5-1.5" ACROSS SOUTHERN MARYLAND...ESPECIALLY ST. MARYS AND CALVERT COUNTIES...MAINLY GRASSY SURFACES. COULD SEE SOME FLAKES AS FAR WEST AS I-95...BUT NOT CURRENTLY EXPECTING ANY ACCUMULATION. HIGH PRESSURE BUILDS IN ON FRIDAY...AND PERSISTS THROUGH SATURDAY. BOTH NORTHERN STREAM AND SOUTHERN STREAM SYSTEMS MOVE TOWARDS THE EAST COAST SATURDAY NIGHT...BUT WILL REMAIN UNPHASED WITH CLIPPER STAYING TO OUR NORTH AND LOW PRESSURE REMAINING WELL TO OUR SOUTH AND OFFSHORE. HIGHS UPPER 30S TO MID 40S FRIDAY AND MID 40S TO NEAR 50F SATURDAY. LOWS IN THE 20S TO LOW 30S...COLDEST FRIDAY NIGHT.
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&& .LONG TERM /SUNDAY THROUGH WEDNESDAY/...
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COASTAL LOW PRESSURE WILL MOVE OUT TO SEA WELL OFF TO OUR SOUTH AND EAST SUNDAY. SURFACE HIGH PRESSURE WILL REMAIN OVERHEAD...BRINGING SEASONABLY CHILLY AND DRY CONDITIONS. CONFIDENCE REMAINS HIGH FOR A HIGH AMPLITUDE PATTERN WITH A POTENT UPPER-LEVEL TROUGH OVERHEAD MONDAY THROUGH WEDNESDAY...BUT THE DETAILS AND TIMING OF THE SHORTWAVE ENERGY ARE HIGHLY UNCERTAIN WHICH LEADS TO A LOW CONFIDENCE FORECAST. LATEST GUIDANCE CONTINUES TO SUGGEST THAT COASTAL LOW PRESSURE MAY DEVELOP MONDAY INTO TUESDAY...BUT THE LATEST TREND IS TO INDICATE THAT IT MAY NOT INTENSIFY RAPIDLY ENOUGH TO AFFECT OUR AREA WITH A SIGNIFICANT WINTER STORM. HOWEVER...GIVEN THE HIGH AMPLITUDE PATTERN THIS IS STILL POSSIBLE AND IT WILL HAVE TO BE MONITORED OVER THE NEXT SEVERAL DAYS. THE LOW SHOULD PULL AWAY FROM THE AREA WEDNESDAY...BUT THE UPPER- LEVEL TROUGH WILL REMAIN OVERHEAD. COLD CONDITIONS ARE EXPECTED AND A FEW SNOW SHOWERS ARE POSSIBLE DUE TO THE UPPER-LEVEL TROUGH.
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&& .AVIATION /08Z THURSDAY THROUGH MONDAY/...
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WIDESPREAD IFR/LIFR CONDITIONS IN FOG...DRIZZLE...AND LOW CLOUDS EARLY THIS MORNING WILL GRADUALLY IMPROVE AS THE MORNING WEARS ON WITH VFR DEVELOPING AREA WIDE AS FRONTAL BOUNDARY CLEARS THE REGION. WILL ALSO SEE WINDS PICK UP OUT OF THE NORTHWEST LATER THIS MORNING AND INTO THE AFTERNOON WITH GUSTS 15-17 KNOTS DEVELOPING. VFR CONDITIONS ARE THEN EXPECTED TO CONTINUE TONIGHT THROUGH SATURDAY. THERE MAY BE A BRIEF PERIOD OF LIGHT SNOW/FLURRIES AT DCA/BWI/MTN LATE TONIGHT...BUT NO SIGNIFICANT IMPACTS/REDUCTIONS ARE CURRENTLY EXPECTED. WINDS BRIEFLY SLACKEN THIS EVENING BEFORE RESTRENGTHENING OUT OF THE NORTHWEST AFTER MIDNIGHT TONIGHT AND ON FRIDAY WITH GUSTS 15-20 KNOTS. VFR CONDITIONS ARE LIKELY FOR SUNDAY. LOW PRESSURE MAY IMPACT THE TERMINALS MONDAY INTO TUESDAY. DETAILS ARE UNCERTAIN AT THIS TIME.
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&& .MARINE...
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LIGHT SOUTH WINDS ARE BEING OBSERVED EARLY THIS MORNING...BUT WINDS WILL TURN TO THE NORTHWEST AND STRENGTHEN AFTER FRONTAL PASSAGE. THUS SMALL CRAFT ADVISORY IS IN EFFECT FOR ALL WATERS INTO THE AFTERNOON HOURS. WINDS SLACKEN BRIEFLY LATE THIS AFTERNOON AND EVENING...SO SCA ONLY FOR LOWER CHESAPEAKE BAY AND LOWER POTOMAC. HOWEVER WINDS WILL INCREASE AGAIN LATER TONIGHT AND ON FRIDAY...WITH SMALL CRAFT ADVISORY IN EFFECT FOR ALL WATERS AGAIN. WIND GUSTS MAY APPROACH GALE FORCE FIRST HALF OF FRIDAY. WINDS WILL THEN WEAKEN AND FALL BELOW SCA CRITERIA FRIDAY NIGHT AND SATURDAY. COASTAL LOW PRESSURE WILL PASS BY WELL TO THE SOUTH AND EAST OF THE WATERS SUNDAY INTO SUNDAY NIGHT. THE GRADIENT MAY BE STRONG ENOUGH FOR WINDS TO APPROACH SCA CRITERIA OVER PORTIONS OF THE WATERS. LOW PRESSURE MAY IMPACT THE WATERS MONDAY INTO TUESDAY. GUSTY WINDS ARE POSSIBLE DURING THIS TIME...BUT DETAILS REMAIN HIGHLY UNCERTAIN. THE LOW WILL MOVE AWAY FROM THE AREA WEDNESDAY AS IT INTENSIFIES. GUSTY NORTHWEST WINDS ARE POSSIBLE.
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&& .HYDROLOGY...
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RAIN HAS ENDED ACROSS THE REGION. RAINFALL AMOUNTS RANGED FROM A HALF INCH TO INCH ACROSS THE POTOMAC...SHENANDOAH AND RAPPAHANNOCK BASINS WITH ISOLATED AMOUNTS UP TO AN INCH AND A QUARTER. THIS COUPLED WITH TEMPERATURES AND DEWPOINTS IN THE 40S/50S ALLOWED MUCH OF THE REMAINING SNOW TO MELT AND FURTHER SATURATE THE SOIL. SMALL STREAMS AND CREEKS ARE MOSTLY ON THE DECLINE EARLY THIS MORNING...ALTHOUGH LARGER RIVERS CONTINUE TO RISE. RIVER FLOOD WARNINGS ARE CURRENTLY IN EFFECT FOR CACAPON...OPEQUON...MONACACY...GOOSE CREEK...POTOMAC FROM POINT OF ROCKS TO EDWARDS FERRY...AND SHENANDOAH AT MILLVILLE FOR FLOODING TODAY. A RIVER FLOOD WATCH CONTINUES FOR POTOMAC RIVER INCLUDING HARPERS FERRY AND LITTLE FALLS. PLEASE SEE FLOOD WATCH AND FLOOD WARNING PRODUCTS FOR MORE INFORMATION.
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&& .TIDES/COASTAL FLOODING...
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TIDAL ANOMALIES AROUND 1 TO 2 FEET CONTINUE EARLY THIS MORNING DUE TO THE SOUTHERLY FLOW. HOWEVER...ASTRONOMICAL NORMS ARE RELATIVELY LOW AND THIS IS THE LOWER OF THE TWO HIGH TIDES. THEREFORE...MINOR COASTAL FLOODING IS NOT EXPECTED AT THIS TIME. AN OFFSHORE FLOW WILL DEVELOP BY 7 AM THIS MORNING ACROSS ALL OF THE WATERS AND THE TIDAL ANOMALIES SHOULD SHARPLY DECREASE. WILL HAVE TO WATCH FOR FRESHWATER INUNDATION ALONG THE UPPER TIDAL POTOMAC RIVER. WATER LEVELS MAY APPROACH MINOR FLOODING THRESHOLDS FOR GEORGETOWN IN WASHINGTON DC LATE FRIDAY NIGHT.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...DENSE FOG ADVISORY UNTIL 7 AM EST THIS MORNING FOR DCZ001. MD...DENSE FOG ADVISORY UNTIL 7 AM EST THIS MORNING FOR MDZ003>006- 011-013-014-502>508. VA...DENSE FOG ADVISORY UNTIL 7 AM EST THIS MORNING FOR VAZ037>040- 050>055-501-502-505-506. WV...DENSE FOG ADVISORY UNTIL 7 AM EST THIS MORNING FOR WVZ050>053- 504. MARINE...SMALL CRAFT ADVISORY UNTIL 1 PM EST THIS AFTERNOON FOR ANZ532- 533. SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 7 PM EST FRIDAY FOR ANZ530>533-535-536-538>542. SMALL CRAFT ADVISORY UNTIL 1 PM EST THIS AFTERNOON FOR ANZ530- 531-535-536-538>542. SMALL CRAFT ADVISORY UNTIL 7 PM EST FRIDAY FOR ANZ534-537-543.
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&& $$ SYNOPSIS...BJL/MJM NEAR TERM...MJM SHORT TERM...MJM LONG TERM...BJL AVIATION...BJL/MJM MARINE...BJL/MJM HYDROLOGY...JE/BJL/MJM TIDES/COASTAL FLOODING...BJL

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