Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 171427 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1027 AM EDT SUN AUG 17 2014 .SYNOPSIS... A WEAK COLD FRONT WILL MOVE INTO THE AREA THIS AFTERNOON BEFORE STALLING OUT OVERHEAD TONIGHT INTO MONDAY. LOW PRESSURE OVER THE OHIO VALLEY WILL TRACK ALONG THE BOUNDARY...PASSING THROUGH OUR AREA MONDAY NIGHT INTO TUESDAY. THE BOUNDARY WILL REMAIN STALLED OVER THE AREA DURING THE MIDDLE AND LATTER PORTIONS OF THE WEEK. && .NEAR TERM /THROUGH TONIGHT/... AT 14Z...VISIBLE SATL IMGRY SHOWING MOSTLY-PARTLY SUNNY SKIES IN AN AREA ACROSS CENTRAL MD SOUTHWEST INTO NORTHERN VIRGINIA. TEMPS IN THIS PATCH AT 14Z HAVE REACHED 81F IN DOWNTOWN BALTIMORE/METRO AND THE UPPER 70S ELSEWHERE. THIS CLEAR SLOT WILL GENERATE RELATIVELY MORE SFC HEATING AND REACH THE MID-UPPER 80S THIS AFTERNOON. USING BOTH NSHARP AND AWIPS INTERACTIVE SKEW-T...APPROX 2000 J/KG2 OF CAPE IS AVAILABLE WITH A T/TD MODIFICATION TO 86/66...AND WITH THE COLD FRONT WITHIN THE CWA...ISOLATED TSTMS CAN`T BE RULED OUT IN AREAS WITHIN THESE RELATIVELY LARGER CAPE VALUES. THOSE AREAS UNDER MOSTLY CLOUDY SKIES WILL ONLY REACH THE LOWER 80S...AND THIS WILL LIMIT THE CAPE TO A0B 1000 J/KG2. SO HAVE TAKEN THUNDER OUT OF GRIDS IN THOSE AREAS THAT ARE CURRENLTY MOSTLY CLOUDY OR CLOUDY...BUT HAVE KEPT IN SCT SHRA ACTIVITY AS THERE IS ENOUGH ENERGY AND A BOUNDARY IN THE VCNTY FOR SHRA TO BE REALIZED AS IS EVIDENCED CURRENTLY WITH THE RADAR DETECTING SHRA ACTICITY IN THE CULPEPPER/FREDERICKSBURG AREA. THESE DIURNALLY-DRIVEN SHOWERS/TSTMS ARE EXPECTED TO DISSIPATE THIS EVE...W/ SKIES REMAINING MOSTLY CLOUDY OVER THE WRN HALF OF THE AREA AND NERN MD SEEING MORE CLEARING. ANOTHER RELATIVELY WARM OVERNIGHT PERIOD AS DEWPOINTS REMAIN ELEVATED IN THE 60S AND MID CLOUD DECKS INSULATE THE AREA. BY THE PREDAWN HRS...SHOWERS ALONG THE LEADING EDGE OF ANOTHER LOW PRESSURE SYSTEM WILL BE APPROACHING THE WINDWARD SIDE OF THE APLCNS IN ERN WV. && .SHORT TERM /MONDAY THROUGH TUESDAY/... THIS NEXT LOW PRESSURE SYSTEM HAS BEEN DEPICTED OVER THE PAST FEW DAYS BY MOST GUIDANCE MEMBERS AS A POTENT AND COMPACT UPPER SHORTWAVE TAPPING INTO A THIN CORRIDOR OF SUBTROPICAL AIR BY THE TIME IT REACHES THE MID-ATLC. THOUGH SOME UNCERTAINTY STILL REMAINS IN TERMS OF THE PLACEMENT AND TIMING OF POTENT PRECIP AND CONVECTIVE ELEMENTS AS THE FEATURES PASSES BY...TRENDS ARE LOOKING LESS AGGRESSIVE FOR OUR AREA. THOUGH LOCALIZED HEAVY RAIN WILL BE POSSIBLE AS THE LOW CROSSES OVER THE AREA LATE MON/EARLY TUE...THE INITIAL STAGES OF THE LOW`S ARRIVAL LOOKS LIKE A HIGH-POP/LOW QPF TYPE OF SCENARIO MON AFTN/EVE. THE MOST FAVORED AREAS WILL BE THE APLCNS AND INTO THE LOWER PIEDMONT REGION. DRIER CONDITIONS OVER NERN MD...THE BALT METRO DOWN INTO PARTS OF THE DC AREA THOUGH A FEW ISOLATED SHOWERS NOT OUT OF THE QUESTION. A POTENT SHORTWAVE AND ITS ASSOCIATED SURFACE LOW WILL TRACK ALONG A STATIONARY BOUNDARY...PASSING THROUGH OUR AREA MONDAY NIGHT INTO TUESDAY MORNING. MOISTURE WILL BE DEEP AHEAD OF THIS SYSTEM...WITH PWATS AROUND 2 INCHES. THE FORCING FROM THE SHORTWAVE AND THE SURFACE LOW WILL TRIGGER SHOWERS AND PERHAPS A FEW THUNDERSTORMS ACROSS MUCH OF THE AREA DURING THIS TIME. CONFIDENCE FOR FLASH FLOODING STILL REMAINS LOW...BUT MODELS HAVE CONVERGED ON A SOLUTION THAT KEEPS THE STRONGEST FORCING FROM THIS SYSTEM TO OUR SOUTH. THIS WOULD PREVENT A SIGNIFICANT THREAT FOR FLASH FLOODING...BUT WITH DEEP MOISTURE AROUND LOCALLY HEAVY RAIN AND LOCALIZED FLASH FLOODING IS STILL POSSIBLE. THE SHORTWAVE AND SURFACE LOW WILL MOVE OFF TO THE EAST TUESDAY AFTERNOON...BUT THE BOUNDARY WILL REMAIN OVERHEAD. A FEW SHOWERS AND THUNDERSTORMS CANNOT BE RULED OUT...BUT COVERAGE WILL BE SCATTERED AND MUCH OF THE TIME MAY ACTUALLY TURN OUT DRY. HUMID AND SEASONABLY WARM CONDITIONS ARE EXPECTED WITH MAX TEMPS IN THE LOWER TO MIDDLE 80S ACROSS MOST LOCATIONS. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... A SUBTROPICAL RIDGE WILL BUILD OVER THE SOUTHEAST CONUS DURING THE MIDDLE PORTION OF THE WEEK BEFORE EXTENDING NORTH INTO THE CENTRAL CONUS BY FRIDAY. THIS WILL CAUSE A NORTHWEST FLOW ALOFT TO DEVELOP OVER OUR AREA. A STATIONARY BOUNDARY WILL REMAIN NEARBY WITH MOST OF OUR AREA REMAINING IN A WARM AND HUMID AIRMASS. SHOWERS AND THUNDERSTORMS ARE POSSIBLE EACH DAY...ESPECIALLY DURING THE AFTERNOON AND EVENING HOURS. MAX TEMPS EACH DAY WILL BE IN THE 80S ACROSS MOST LOCATIONS. UPPER-LEVEL LOW PRESSURE MAY DEVELOP OFF THE EAST COAST NEXT WEEKEND WHILE HIGH PRESSURE BUILDS INTO NEW ENGLAND. THIS WOULD CAUSE A BACKDOOR COLD FRONT TO MOVE THROUGH OUR AREA...ALLOWING FOR COOLER MARINE AIR TO MOVE IN. && .AVIATION /14Z SUNDAY THROUGH THURSDAY/... NEARLY ALL OBS FOR THE AREA WERE CALM AND CLEAR STARTING OUT THE NIGHT...BUT NOW A FAIRLY DENSE MID/UPPER COLLECTION OF CLOUD DECKS HAVE MADE THEIR WAY OVER THE AREA. LIGHT SW FLOW HAS ALSO PICKED-UP A BIT...W/ THIS STORY CONTINUING TO PLAY-OUT FOR THE NEXT SEVERAL HRS. ONLY ISOLATED SHOWERS POSSIBLE FOR THE FIRST HALF OF THE TAF PERIOD...W/ MORE SCATTERED ACTIVITY - AND POSSIBLY A QUICK TSTM LATER THIS AFTN. OTHERWISE...VFR CONDS THRU THE CURRENT PERIOD AND DISSIPATION IN THIS ACTIVITY AGAIN LATE TONIGHT. LOW PRESSURE WILL PASS THROUGH THE TERMINALS MONDAY NIGHT INTO TUESDAY...LIKELY TRIGGERING SHOWERS AND FEW THUNDERSTORMS. SUBVFR CONDITIONS ARE POSSIBLE IN CONVECTION. AN UNSETTLED PATTERN IS EXPECTED THROUGH THE MIDDLE PORTION OF NEXT WEEK...WITH SHOWERS AND THUNDERSTORMS POSSIBLE EACH DAY...MAINLY DURING THE AFTERNOON AND EVENING HOURS. A WARM AND HUMID AIRMASS MAY LEAD TO LOW CLOUD AND AREAS OF FOG DURING THE OVERNIGHT AND MORNING HOURS EACH DAY. && .MARINE... A LIGHT BUT STEADY SW WIND CONTINUES TO MOVE ACROSS THE WATERS OVERNIGHT...CONTINUING THROUGHOUT THE DAY. PERIODS OF SLIGHTLY HIGHER GUSTS NEAR 15KT POSSIBLE AT TIMES...BUT THAT WILL BE THE EXCEPTION. A SOLID 10KT BREEZE THIS AFTN WILL DROP OFF AGAIN LATE TONIGHT...AS WINDS SWITCH AROUND BRIEFLY TO NLY. THE TAIL END OF A COLD FRONT IS EXPECTED TO SLIDE DOWN THE BAY W/ SOME LIGHT NLY CHANNELING...THEN A WEAK ONSHORE FLOW DURING THE DAYTIME HRS ON MON. LOW PRESSURE WILL PASS THROUGH THE WATERS LATE MONDAY NIGHT INTO TUESDAY. WINDS MAY APPROACH SCA CRITERIA...BUT THE GRADIENT APPEARS TO BE WEAK SO GUSTS HAVE BEEN CAPPED AT 15 KNOTS. A STATIONARY BOUNDARY WILL REMAIN NEAR THE WATERS FOR THE MIDDLE AND LATTER PORTIONS OF THE WEEK. THIS MAY TRIGGER A FEW SHOWERS AND THUNDERSTORMS...MAINLY DURING THE AFTERNOON AND EVENING HOURS EACH DAY. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...BJL NEAR TERM...LEE/GMS SHORT TERM...BJL/GMS LONG TERM...BJL AVIATION...BJL/GMS MARINE...BJL/GMS

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