Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 030115 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 915 PM EDT WED SEP 2 2015 .SYNOPSIS... WEAK HIGH PRESSURE WILL BE LOCATED OVER THE CENTRAL APPALACHIANS TONIGHT. AN UPPER LEVEL DISTURBANCE WILL CROSS THE AREA THURSDAY INTO THURSDAY NIGHT. A BACKDOOR COLD FRONT MOVES INTO THE AREA FRIDAY. HIGH PRESSURE THEN RETURNS FOR THE WEEKEND INTO EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... SHORTWAVE TROUGH IS NOW EXITING THE AREA TO THE SOUTHEAST AND THE FORECAST AREA IS DRY. WILL CARRY A DRY FORECAST OVERNIGHT FOR NOW...BUT THERE IS ANOTHER MID LEVEL FEATURE (BETTER SEEN IN SATELLITE DATA THAN MODEL DATA) ENTERING NORTHERN PA. GOOD NEWS IS THAT CONVECTION ASSOCIATED WITH IT IS DISSIPATING. BUT WORTH NOTING SOME BLIPS OF PRECIPITATION DO SHOW UP IN SOME OF THE MODEL DATA AFTER MIDNIGHT. SKIES HAVE CLEARED BEHIND THE SHORTWAVE...HASTENING RADIATIONAL COOLING OF ALREADY RAIN-LOWERED TEMPS. ALREADY SEEING SOME VSBY DROPS IN THE SHENANDOAH VALLEY AND CENTRAL MD. ODDS ARE WE WILL HAVE AT LEAST SOME DENSE FOG OVERNIGHT. QUESTION IS HOW WIDESPREAD WILL IT BE (ESPECIALLY SINCE RAIN WAS NOT UNIFORM)...HOW LOW VSBYS WILL DROP...AND IF UPSTREAM CLOUDS WILL PLAY A ROLE. WILL HAVE TO WATCH THE TRENDS FOR NOW. LOW TEMPERATURES NEAR THE DEW POINTS IN MID TO UPPER 60S SEEM REASONABLE...WITH LOWER 70S IN URBAN/COASTAL LOCATIONS. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... H5 RDG AXIS WL RESIDE ACRS THE MS VLY THU...WHICH PLACES CWFA IN THE NW FLOW. HWVR...THE AMS WL BE JUST AS WARM...HUMID...AND UNSTBL AS TDA. WUD XPCT DIURNALLY DRIVEN TSRA TO DVLP ALNG THE MTNS DURING THE AFTN. THERES CONSISTENT MDL EVIDENCE THAT THESE STORMS WL EMERGE FM THE MTNS AND TRACK INTO THE CSTL PLAIN BY EVNG. TIMING SPECIFIC VORTS PROBLEMATIC AT THIS POINT...BUT WUD THINK THAT ALL OF THIS ACTIVITY WL CLEAR CWFA BEFORE DAWN. HVNT MADE ANY BIG ADJUSTMENTS TO TEMPS...AS PERSISTENCE SHUD PROVE TO BE A GOOD FCSTG MODEL. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... MAIN WEATHER FEATURE DURING THE LONG TERM WILL BE A BACKDOOR COLD FRONT THAT MOVES THROUGH FRIDAY AFTERNOON AND EVENING...PROVIDING RAIN CHANCES FOR THE ENTIRE AREA. ATTM...KEPT POPS AT CHANCE EVERYWHERE...AS NOT ALL GUIDANCE SUGGESTS WIDESPREAD COVERAGE. WHILE CAPE WILL BE LOW/MODERATE...GENERALLY AOA 1000 J/KG...EBS NEARLY NONEXISTENT...SO EXPECT PULSE-TYPE ACTIVITY AND HEAVY RAINERS AS INDIVIDUAL CELLS MOVE VERY SLOWLY. CLOUD COVER...ONSHORE FLOW...AND FRONTAL PASSAGE SHOULD WORK IN CONCERT TO KEEP TEMPERATURES A FEW DEGREES LESS THAN PREVIOUS DAYS. HOWEVER...STILL EXPECT TEMPERATURES A FEW DEGREES AOA NORMAL. PRECIP CHANCES SHOULD DWINDLE QUICKLY AFTER DUSK FRIDAY NIGHT WITH LOSS OF INSTABILITY. VERY LITTLE DAY-TO-DAY VARIABILITY IN SENSIBLE WEATHER THROUGH THE REMAINDER OF THE EXTENDED...AS HIGH PRESSURE BUILDS IN SATURDAY AND REMAINS THROUGH THE MIDDLE OF NEXT WEEK. WITH WARM MID-LEVEL TEMPERATURES...LAPSE RATES WILL BE VERY POOR...CONSEQUENTLY CHANCES FOR PRECIP DURING THIS PERIOD APPEAR VERY LOW AND GENERALLY WOULD ONLY BE CONFINED TO THE HIGHER TERRAIN IN THE WEST. ELSEWHERE...EXPECT HIGH TEMPERATURES NEAR NORMAL THROUGH THE WEEKEND...WITH DEWPOINTS FALLING INTO THE U50S BY SUNDAY. BY MONDAY...TEMPERATURES START CREEPING BACK ABOVE NORMAL AND BY TUESDAY SOME AREAS COULD BE BACK INTO L90S. && .AVIATION /01Z THURSDAY THROUGH MONDAY/... DRY CONDITIONS EXPECTED FOR THE REMAINDER OF THE NIGHT. MOST OF THE TAF SITES MISSED RAINFALL TODAY...PUTTING THE EXTENT OF FOG DEVELOPMENT IN QUESTION. ENOUGH OF A GUIDANCE SIGNAL AT CHO TO INTRODUCE IFR THERE. EXPECT ADJUSTMENTS TO TAFS AS TRENDS ARE MONITORED OVERNIGHT. A SIMILAR FORECAST FOR THURSDAY...WITH VFR AND LIGHT WINDS UNTIL THUNDERSTORMS DEVELOP IN THE AFTERNOON/EVENING. ALL ACTIVITY SHOULD BE SEVERAL HOURS LATER THAN TODAY...AND COVERAGE PERHAPS LESS EXTENSIVE. BRIEF/LOCALIZED FLIGHT IMPACTS POSSIBLE. SUB-VFR POSSIBLE FRIDAY AFTERNOON AS BACKDOOR COLD FRONT MOVES THROUGH THE REGION. VFR CONDITIONS RETURN SATURDAY THROUGH THE EXTENDED UNDER HIGH PRESSURE. && .MARINE... DRY CONDITIONS THROUGH TONIGHT WITH NW WINDS LESS THAN 10 KT. NW FLOW THRU THU WILL STAY BELOW SCA CRITERIA. ANOTHER ROUND OF SCT TSRA PSBL LATE DAY INTO THE EVNG...MOSTLY STAYING W OF THE MARINE AREA BUT THE PTMC RIVER WL BE ON THE EDGE OF THE HIEST POTL RGN. WINDS EXPECTED NEAR SCA FRIDAY AFTERNOON THROUGH SATURDAY EVENING...AS BACKDOOR COLD FRONT MOVES THROUGH THE REGION. COLD FRONT WILL ALSO BRING CHANCE FOR SHOWERS AND THUNDERSTORMS OVER THE WATERS FRIDAY AFTERNOON AND EVENING. WINDS SHOULD SUBSIDE BELOW SCA LATE SATURDAY INTO SUNDAY MORNING AND THROUGH THE EXTENDED. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...ADS/MSE NEAR TERM...ADS SHORT TERM...HTS LONG TERM...MSE AVIATION...ADS/MSE MARINE...ADS/MSE/HTS

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