Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 201827 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 227 PM EDT MON OCT 20 2014 .SYNOPSIS... HIGH PRESSURE WILL MOVE OFFSHORE THIS AFTERNOON. A COLD FRONT WILL APPROACH FROM THE WEST TONIGHT AND MOVE THROUGH THE REGION TUESDAY. LOW PRESSURE WILL PERSIST NEAR THE MID-ATLANTIC COAST INTO THURSDAY. HIGH PRESSURE WILL RETURN FOR THE END OF THE WORKWEEK AND INTO THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... HIGH PRESSURE RESIDES OVER EASTERN VA/NC THIS AFTERNOON. SURFACE AND UPPER LOW PRESSURE HAS MOVED INTO THE UPPER GREAT LAKES...WITH A TRAILING SURFACE COLD FRONT OVER THE WESTERN OHIO VALLEY. BOTH AN UPPER TROUGH AND SURFACE COLD FRONT WILL APPROACH FROM THE WEST THROUGH TONIGHT. SOME LIGHT RETURNS HAVE MOVED INTO THE POTOMAC HIGHLANDS...AND ISOLATED RAIN HAS BEEN NOTED ON SURFACE OBS OVER ERN WV. WITH RELATIVELY DRY AIR AT LOW LEVELS AND DEW POINT DEPRESSIONS AROUND 10-15 DEGREES...RAIN WILL HAVE DIFFICULTY MAKING IT TO THE GROUND. FCST CALLS FOR ISOLATED SHOWERS OVER THE POTOMAC HIGHLANDS INITIALLY...SPREADING EWD INTO THE SHENANDOAH VALLEY BY LATE AFTERNOON AND INTO THE I-95 CORRIDOR BY THIS EVENING. ANY RAIN SHOULD BE ISOLATED TO SCATTERED WITH LIKELY JUST A FEW HUNDREDTHS OF AN INCH ACCUMULATION FOR THOSE AREAS THAT DO SEE RAIN. IN TERMS OF TEMPS AND WINDS...HIGHS LATE THIS AFTERNOON GENERALLY IN THE 60S UNDER SOUTHERLY FLOW WITH SOME GUSTS TO 2O MPH. WINDS BECOME LIGHT TONIGHT. LOW TEMPS WILL BE AROUND 50 ALONG AND EAST OF I-95...AND IN THE 40S ELSEWHERE. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... SURFACE COLD FRONT MOVES THROUGH TUESDAY. AN UPPER LOW WILL DROP FROM THE GREAT LAKES INTO PA AND NORTHERN PORTIONS OF WV/MD/VA BY TUESDAY AFTERNOON...AND THEN OVER THE MID-ATLANTIC TUESDAY NIGHT. WITH SOME INSTABILITY AND PERIODS OF VORTICITY ADVECTION...POTENTIAL FOR SCATTERED RAIN/SHOWERS WILL CONTINUE. TEMPS AROUND 10 DEGREES BELOW NORMAL TUESDAY...WITH HIGHS PRIMARILY IN THE 50S. LOWS TUESDAY NIGHT IN THE 40S AGAIN...AND AROUND 50 IN URBAN AREAS AND BY CHESAPEAKE BAY. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... UPPER LEVEL LOW PRESSURE WILL REMAIN OCCLUDED AND STRENGTHEN NEAR THE MID-ATLANTIC THROUGH THE DAY WEDNESDAY AND WEDNESDAY NIGHT. THE ASSOCIATED SURFACE LOW WILL DEEPEN DUE TO BAROCLINIC ENHANCEMENT AS IT MOVES OVER RELATIVELY WARM OCEAN WATERS OFF OF THE MID-ATLANTIC COAST DURING THIS TIME. POPS WILL REMAIN FOCUSED OVER THE NORTHEASTERN HALF OF THE CWA AS STORMS PRECIP SHIELDS SLOWLY STAGGERS NORTHEASTWARD WITH THE LOW. WE SHOULD SEE A RESPECTABLE QPF GRADIENT WITH THE AREAS ALONG AND JUST WEST OF THE BAY RECEIVING ONLY A COUPLE OF TENTHS OF AN INCH OF RAINFALL WHILE LOCATIONS ON THE THE DELMARVA PENINSULA WILL SEE SIGNIFICANTLY MORE DUE TO THEIR PROXIMITY OT THE LOW. THE MAJOR FORECAST CHALLENGE ON THE BACKSIDE OF THE LOW IS THE UPSLOPE PRECIP THREAT. THE HIGHEST ELEVATIONS ALONG THE POTOMAC HIGHLANDS WILL SEE LOW TEMPS THAT MAY DIP INTO THE MID 30S WEDNESDAY NIGHT...AND GIVEN THE FETCH OF THE NORTHERLY WINDS OVER THE GREAT LAKES UPSTREAM OF THE ALLEGHENY FRONT THE OPTION TO INCLUDE SNOW AS A PRECIP TYPE WAS TEMPTING. BUT IT LOOKS LIKE THE LAYER OF ABOVE-FREEZING AIR NEAR THE SURFACE WILL BE A BIT TOO THICK FOR ANY SNOWFALL. THIS MAY CHANGE IN UPCOMING FORECASTS AS CONFIDENCE IN LOW TEMPS INCREASES...BUT EVEN IF A FEW FLAKES DO FALL NO ACCUMULATION WILL OCCUR. HIGH PRESSURE CENTERED OVER THE SOUTHEASTERN UNITED STATES WILL NOSE INTO THE AREA FRIDAY AND CONTINUE TO STRENGTHEN THROUGH THE WEEKEND. OVERALL...SATURDAY AND SUNDAY SHOULD BE BEAUTIFUL FALL DAYS WITH DRY CONDITIONS AND HIGHS IN THE MID-60S. HIGH PRESSURE WILL BEGIN TO SHIFT OFF OF THE MID-ATLANTIC COAST EARLY NEXT WORKWEEK AND OUR NEXT THREAT FOR ADVERSE WEATHER SHOULD NOT PRESENT ITSELF UNTIL THE MIDDLE OF NEXT WEEK. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... VFR CONTINUES THROUGH TODAY AS THE HIGH SHIFTS OFFSHORE WITH RETURN SLY/SWLY FLOW GUSTING UP TO 18 KT THIS AFTERNOON. A COLD FRONT WILL APPROACH FROM THE WEST TONIGHT AND MOVE THROUGH THE REGION TUESDAY. PERIODIC SHOWERS AND SUB-VFR POSSIBLE...BUT CONFIDENCE TOO LOW TO INCLUDE AT THE END OF THE TAF PERIOD AT THIS TIME. LIGHT W WINDS TUESDAY. CONFIDENCE IS LOW IN THE OCCURRENCE OF AVIATION HAZARDS THROUGH THE LONG TERM PERIOD. && .MARINE... SCA IN EFFECT FOR GUSTY SOUTHERLY WINDS. GUSTS OVER MOST ZONES WILL DECREASE LATE THIS AFTERNOON AND EARLY EVENING. SCA EXPIRES AT 8 PM FOR MOST ZONES...EXCEPT FOR THE MD CHES BAY SOUTH OF POOLES ISLAND AND THE LOWER TIDAL POTOMAC WHERE SOUTHERLY CHANNELING IS EXPECTED TO CONTINUE UNTIL 2 AM. WLY FLOW TUESDAY AS LOW PRESSURE APPROACHES FROM THE NORTHWEST. LIGHT S WINDS EXPECTED LATE TONIGHT...TRENDING TOWARDS THE WEST AND EVENTUALLY NW DURING THE DAY TUESDAY. A SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED WEDNESDAY AND WEDNESDAY NIGHT AS LOW PRESSURE DEEPENS JUST OFF OF THE MID-ATLANTIC COAST. A SMALL CRAFT ADVISORY MAY ALSO BE NEEDED THURSDAY THROUGH FRIDAY NIGHT AS BREEZY NORTHERLY WINDS FILL IN BEHIND LOW PRESSURE DEPARTING OFF TO THE NORTHEAST. && .TIDES/COASTAL FLOODING... ANOMALIES BACK ON THE RISE...APPROACHING 1 FT LATE THIS AFTERNOON UNDER SOUTHERLY WINDS. FORECASTS FOR WASHINGTON CHANNEL...BALTIMORE AND ANNAPOLIS SHOW LIKELIHOOD TO REACH ACTION STAGES IN THE NEXT TWO HIGH TIDE CYCLES LATE TODAY AND OVERNIGHT...BUT AT THIS TIME FALL SHORT OF MINOR INUNDATION. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR ANZ530>533-535-536-538>542. SMALL CRAFT ADVISORY UNTIL 2 AM EDT TUESDAY FOR ANZ534-537-543. && $$ SYNOPSIS...KCS NEAR TERM...KCS SHORT TERM...KCS LONG TERM...CEB AVIATION...KCS/CEB MARINE...KCS/CEB TIDES/COASTAL FLOODING...KCS

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