Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 211345 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 945 AM EDT MON JUL 21 2014 .SYNOPSIS... HIGH PRESSURE WILL REMAIN ALONG THE EASTERN SEABOARD EARLY THIS WEEK. TEMPERATURES WILL SLOWLY RISE THROUGH WEDNESDAY AHEAD OF A COLD FRONT EXPECTED TO MOVE INTO THE AREA THURSDAY. HIGH PRESSURE IS EXPECTED TO RETURN TO THE MID ATLANTIC STATES TO END THE WORKWEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... HIGH PRESSURE CONTINUES TO BE LOCATED FROM THE NEW ENGLAND COAST DOWN THROUGH THE MID-ATLANTIC...KEEPING AN EAST-SOUTHEAST LOW LEVEL FLOW ACROSS THE CWA. HAVE A FEW LIGHT SHOWERS/SPRINKLES OCCURRING ALONG THE LEE OF THE BLUE RIDGE...OTHERWISE CWA IS DRY AT 13Z BUT WITH PLENTY OF CLOUDS. EXPECTATION IS FOR AN INCREASE IN SHOWER COVERAGE FOR THE AFTERNOON...PRIMARILY NEAR AND WEST OF THE BLUE RIDGE AS INDICATED BY THE SREFS. MOISTURE AND INSTABILITY ARE FORECAST TO BE A LITTLE BETTER THAN YESTERDAY...SO THERE COULD BE ISOLATED THUNDERSTORMS AS WELL ALTHOUGH GIVEN EASTERLY FLOW ANY THUNDERSTORMS MAY BE RELEGATED MORE TOWARD THE FOOTHILLS/SHENANDOAH VALLEY AREA. STUCK WITH A BLEND OF BIAS CORRECTED SREFS AND ADJMAV FOR MAXIMA TODAY...STAYING BELOW NORMAL FOR THIS TIME OF THE YEAR. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... ANY CNVCTN THAT DOES FORM THIS AFTN SHOULD WANE DURG THE EVE HRS. SKIES CONTINUING TO BE M CLDY. OVRNGT TEMPS WL DROP INTO THE 60S ACROSS THE MAJORITY OF THE AREA...LM70S IN THE CITIES AND ALONG THE BAY. && .LONG TERM /TUESDAY THROUGH SUNDAY/... TUESDAY THROUGH WEDNESDAY NIGHT/ FAST ZONAL UPPER FLOW WILL CARRY THE NEXT WX-MAKER ACROSS THE US/CANADA BORDER TODAY AND INTO TMRW. THE SYSTEM WILL EFFECTIVELY SPLIT W/ THE MORE DYNAMIC NRN SECTION SPEEDING OFF TO THE EAST ACROSS ERN QUEBEC...WHILE THE REST OF THE WAVE DIGS DOWN ACROSS THE GREAT LAKES. AS THIS ACTION IS TAKING PLACE WELL OFF TO OUR NORTH AND WEST...THE MID-ATLC WILL AGAIN BE SITTING UNDER AN UNCHANGED AIRMASS FOR THE FIRST HALF OF THE WEEK. ANOTHER LARGE BERMUDA HIGH WILL SET UP OFF THE ATLC COAST AND REINFORCE MORE SUMMER-LIKE CONDITIONS UNTIL THE FRONTAL PASSAGE LATER IN THE WEEK. RELATIVE TO OTHER FAIRLY SIMILAR SET-UPS THIS SUMMER...NOT AN INTENSE LOW LEVEL MOISTURE SURGE OR ANOMALOUSLY HOT PERIOD BUT STILL UNCOMFORTABLY HUMID W/ DAILY HIGHS IN THE U80S/L90S AND DEWPOINTS HOVERING AROUND THE 70 DEG MARK - WHICH IS PLENTY MOIST TO ADD AT LEAST A COUPLE/FEW DEG FOR THE HEAT INDICES EACH AFTN. TUE AND WED WILL BE THE BUILD-UP DAYS FOR THE EVENTUAL FRONTAL PASSAGE EXPECTED BY THU NIGHT. AS THE COLD FRONT SLOWLY MOVES TOWARD THE AREA FROM THE UPPER MIDWEST...THE APLCNS WILL BE THE FOCUS FOR DAILY INITIATION OF SHOWER/TSTM ACTIVITY UNDER WEAK/LIGHT BOUNDARY LAYER AND UPPER FLOW. DAILY PRECIP WILL BE A FUNCTION OF TERRAIN CIRCULATION INTERACTIONS...SFC BOUNDARIES...LEFTOVER CONVECTIVE BOUNDARIES...ETC. WEAK AND SUBTLE CONVERGENCE ZONES WILL LIKELY DEVELOP AND CARRY PRECIP ACTIVITY EACH DAY AND NIGHT UNTIL THE ARRIVAL OF THE FRONT. THURSDAY THROUGH SUNDAY/ A SECONDARY UPPER LEVEL VORT WILL SURGE BEHIND THE INITIAL ONE RESPONSIBLE FOR THE SFC COLD FRONT EARLY THU. THIS WILL HELP PUSH THE BOUNDARY ALONG ITS WAY AND FURTHER TO THE SOUTH AND EAST DURING THE DAY. CONVECTIVE ACTIVITY FROM LATE WED NIGHT WILL LARGELY DISSIPATE OVERNIGHT BUT A FEW RESIDUAL POCKETS OF SHOWER AND WEAK CONVECTION WILL CONTINUE INTO THE MRNG HRS THU. AFTER A BRIEF BREAK THU MRNG...THE COLD FRONT WILL BE ON THE DOORSTEP OF THE APLCNS BY MIDDAY. LATEST GFS SOUNDINGS SHOW ONLY MODEST INSTABILITY VALUES FOR THE AREA AHEAD OF THE FRONT...WHICH WILL TAKE A BETTER PART OF THE DAY TO CLEAR THE AREA - ALLOWING FOR A LONG DAY OF ISOLATED TO SCATTERED SHOWERS/TSTMS. NOT EXPECTING LONG-LIVED OR WIDESPREAD ACTIVITY BUT THE ANTECEDENT CONDITIONS OF RELATIVELY HIGH BOUNDARY MOISTURE...HEATING AND SLIGHTLY HIGHER SHEAR WILL ALLOW FOR PERIODS OF PRECIP THROUGHOUT THE DAY. THE FRONT WILL LIKELY CLEAR THE AREA LATE THU...BUT THEN STILL BE JUST TO OUR SOUTH TO BEGIN FRI. SOME LINGERING SHOWER ACTIVITY WILL HANG AROUND THE SRN PERIPHERY OF THE CWA EARLY FRI AND THE CNTRL APLCNS BUT THEN CONTINUE ON TOWARD THE SE THROUGHOUT THE DAY. A LARGE UPPER RIDGE WILL BEGIN BUILDING OVER THE CNTRL ROCKY MTN REGION...CAUSING THE GREAT LAKES UPPER TROF TO SURGE DOWN THE REMAINDER OF THE EAST COAST. THIS WILL NOT ONLY CLEAR OUT THE AREA OF PRECIP CHANCES HEADING INTO THE WEEKEND...BUT SEND TEMPS AND DEWPOINTS BACK DOWN INTO THE RELATIVELY LOWER CONDITIONS WE`VE SEEN SEVERAL TIMES THIS SUMMER SEASON. && .AVIATION /13Z MONDAY THROUGH FRIDAY/... HAVE AN AREA OF MVFR CLOUDS WEST OF INTERSTATE 95 BACK TOWARD THE SHENANDOAH VALLEY EARLY THIS MORNING...AFFECTING IAD-CHO-MRB. THESE ARE LIKELY TO LINGER THROUGH MUCH OF THE MORNING BEFORE EXPECTED IMPROVEMENT TO VFR. VFR PREVAILS THROUGH THE REST OF THE AFTERNOON/EVENING WITH SCATTERED SHOWERS AROUND. THERE IS THE POTENTIAL FOR STRATUS /MVFR/IFR/ AGAIN OVERNIGHT INTO TUESDAY MORNING. HIGH PRESSURE OFF THE ATLC COAST WILL SET-UP A DAILY SFC FLOW OF MOISTURE AND GRADUALLY INCREASING HEAT TUE. SCATTERED SHOWERS AND TSTMS WILL BE POSSIBLE...ESPEC ACROSS THE MTNS AND NEARBY ZONES BUT LOWER CHANCES TOWARD THE COAST TUE AND INTO WED. BETTER CHANCES FOR MORE WIDESPREAD ACTIVITY ON THU...AS A COLD FRONT SLOWLY MOVES TOWARD AND EVENTUALLY THRU THE AREA LATER IN THE DAY. DRY AND COOLER AIR WILL THEN SWEEP THIS ACTIVITY OFF THE COAST INTO THE WEEKEND. && .MARINE... HIGH PRESSURE ALONG THE COAST KEEPS A SOUTHEAST FLOW IN PLACE TODAY...ALTHOUGH WEAK GRADIENT SHOULD KEEP SPEEDS 10 KT OR LESS. WINDS TURN MORE TO THE SOUTH TONIGHT INTO TUESDAY...CHANNELLING LIKELY TO PROMOTE WINDS INCREASING CLOSER TO 15 KT UP THE MAIN CHANNEL OF THE BAY. LIGHT S-SW FLOW WED AND MAXIMIZES JUST BEFORE THE PASSAGE OF A COLD FRONT ON THU. EVEN AFTER THE FRONTAL PASSAGE...ONLY A STEADY 10KT NW WINDS EXPECTED...WHICH WILL REMAIN LIGHT INTO THE WEEKEND. && .TIDES/COASTAL FLOODING... ANOMALIES HAVE INCREASED TO AROUND 1 FT ABOVE NORMAL THIS MORNING. WILL HAVE TO KEEP AN EYE ON ANNAPOLIS FOR THIS AFTERNOON/S CYCLE...BUT CURRENTLY /AS FORECAST BY CBOFS/ EXPECT WATER LEVELS TO REMAIN BELOW MINOR THRESHOLDS FOR THE EARLY AFTERNOON HIGH TIDE CYCLE. TONIGHT/S ON THE OTHER HAND WILL BE THE HIGHER OF THE NEXT TWO...AND WITH ANOMALIES CONTINUING TO INCREASE IT IS BECOMING MORE LIKELY THAT SENSITIVE AREAS ON THE WESTERN SHORE OF THE CHESAPEAKE BAY WILL EXPERIENCE MINOR TIDAL FLOODING. THIS HAS BEEN ADDED TO THE HWO. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...BPP NEAR TERM...BPP SHORT TERM...BAJ LONG TERM...ABW AVIATION...BPP/BAJ/ABW MARINE...BPP/BAJ/ABW TIDES/COASTAL FLOODING...BPP

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