Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 041516 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1016 AM EST THU FEB 4 2016 .SYNOPSIS... 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. && .NEAR TERM /THROUGH TONIGHT/... A COLD FRONT HAS MOVED THROUGH THE REGION AND IS NOW LOCATED ALONG THE EAST COAST THIS MORNING. THE PRESSURE PATTERN WILL NOT CHANGE MUCH TODAY AS THE FRONT REMAINS STATIONARY. COLD AIR ADVECTION WILL MOVE INTO THE REGION FROM WEST TO EAST TODAY AND TONIGHT. HIGH TEMPS WILL RANGE FROM THE U30S/L40S ACROSS THE HIGHLANDS TO THE L50S ACROSS THE PIEDMONT AND SOUTHERN MD. A DEEP TROUGH WILL APPROACH THE OHIO VALLEY TODAY AND A WAVE OF LOW PRESSURE WILL MOVE NORTHWARD FROM THE CAROLINAS TODAY. RAIN IS EXPECTED TO MOVE NORTHWARD ACROSS EASTERN VA AND INTO SOUTHERN MARYLAND BY THIS AFTERNOON. LOW PRESSURE WILL CONTINUE TO INTENSIFY OFF OBX TONIGHT. COLD AIR ADVECTION WILL CONTINUE TO MOVE INTO THE REGION FROM THE WEST AND 850 TEMPS WILL DROP BELOW FREEZING BY 12Z FRIDAY. SFC TEMPS WILL ALSO DROP INTO THE 30S OVERNIGHT. RAIN IS EXPECTED TO CHANGE OVER TO SNOW LATE TONIGHT INTO EARLY FRIDAY. AT THIS TIME...FORECAST MODELS ARE IN AGREEMENT THAT 0.1-0.25 INCHES OF LIQUID IS FORECAST ACROSS THE TIDEWATER REGION...SOUTHERN MD TO SOUTHERN BALTIMORE WITH LESSER AMOUNTS REACHING I-95. HOWEVER...LIGHTER AMTS MAY STILL LEAD TO LITTLE ACCUMULATION NEAR I-95. AT THIS TIME...MAINTAINING THE CURRENT SNOWFALL FORECAST AS 12Z MODEL GUIDANCE COMES INTO THE OFFICE. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... 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. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... 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. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... VFR CONDITIONS EXPECTED TODAY. NW WINDS EXPECTED TODAY WITH GUSTS UP TO 18 KTS POSSIBLE. 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. && .MARINE... FRONT CROSSING THE POTOMAC AND CHESAPEAKE NOW WITH NORTHWEST WINDS PICKING UP BEHIND IT. 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. && .HYDROLOGY... 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...SENECA CREEK AT DAWSONVILLE...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. && .TIDES/COASTAL FLOODING... AN OFFSHORE FLOW WILL DEVELOP EARLY THIS MORNING AND THIS WILL CAUSE TIDAL ANOMALIES TO DECREASE FOR MOST AREAS. WILL HAVE TO WATCH FOR FRESHWATER INUNDATION ALONG THE UPPER TIDAL POTOMAC RIVER...PARTICULARLY NEAR GEORGETOWN. WATER LEVELS MAY APPROACH MODERATE FLOODING THRESHOLDS. A COASTAL FLOOD WATCH IS IN EFFECT. THE BEST CHANCE FOR MODERATE FLOODING TO OCCUR WILL BE AROUND HIGH TIDE LATE TONIGHT...AND AGAIN AROUND HIGH TIDE LATER FRIDAY AFTERNOON INTO FRIDAY EVENING. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...COASTAL FLOOD WATCH FROM 3 PM EST THIS AFTERNOON THROUGH FRIDAY EVENING FOR DCZ001. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 1 PM EST THIS AFTERNOON FOR ANZ530>533-535-536-538>542. SMALL CRAFT ADVISORY FROM 7 PM THIS EVENING TO 7 PM EST FRIDAY FOR ANZ530>533-535-536-538>542. SMALL CRAFT ADVISORY UNTIL 7 PM EST FRIDAY FOR ANZ534-537-543. && $$ SYNOPSIS...BJL/MM NEAR TERM...MM/HAS SHORT TERM...MM LONG TERM...BJL AVIATION...BJL/MM MARINE...BJL/MM HYDROLOGY...LWX TIDES/COASTAL FLOODING...LWX

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