Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 100102 AAA AFDLWX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 902 PM EDT WED JUL 9 2014 .SYNOPSIS... A COLD FRONT WILL SLOWLY MOVE INTO THE AREA TONIGHT. THE BOUNDARY WILL STALL OUT AND DISSIPATE OVER THE REGION FOR THURSDAY AND FRIDAY. HIGH PRESSURE OVER THE ATLANTIC WILL BRING HOT AND HUMID CONDITIONS FOR THE WEEKEND INTO EARLY NEXT WEEK. && .NEAR TERM /TONIGHT/... A SECOND-STRAIGHT ACTIVE DAY ACROSS MUCH OF THE AREA...THOUGH A SHORTER-DURATION EVENT AND MORE CONFINED TO AREAS E OF THE BLUE RIDGE. WE ARE STILL UNDER THE ZONE OF HIGHER MOISTURE AND HEATING POTENTIAL W/ THE LARGE-SCALE UPPER TROUGH AXIS STILL BACK TO OUR WEST. UNTIL THIS FEATURE CLEARS THE EAST COAST...THE POTENTIAL WILL CONTINUE TO DIURNAL SHOWERS/TSTMS ACROSS THE AREA. ISOLATED SHOWERS WILL BE POSSIBLE INTO THE LATE NIGHT HRS TONIGHT...BUT A ONLY A FEW LOCALES AND ATTM - IN THE MID-PART OF THE NRN VA BLUE RIDGE S OF FRONT ROYAL. LOSS OF THE SUN WILL LIKELY DISSIPATE THIS ACTIVITY SHORTLY. EVIDENCE THAT WE`RE STILL UNDER THE SAME AIRMASS...DEWPOINTS E OF I-81 ARE STILL IN THE U60-L70S AND SOME LOCALES HAVE SEEN AN INCREASE SINCE EARLIER THIS EVE. THE SFC WINDS HAVE DROPPED OFF FROM A STEADY S-SW BREEZE TO NEARLY CALM. THE COMBINATION OF THESE ELEMENTS HAVE A WARM OVERNIGHT PERIOD IN STORE FOR THE AREA...THOUGH THE APLCNS HAVE SEEN A DECENT DROP IN DEWPOINTS SO THEY WILL SEE SOME LOWS IN THE U50S-L60S. && .SHORT TERM /THURSDAY/... AN UPPER-LEVEL TROUGH WILL BUILD OVERHEAD THURSDAY THROUGH TMRW NIGHT. THE COLD FRONT OVER THE REGION WILL GRADUALLY DISSIPATE...AND A LIGHT RETURN FLOW WILL DEVELOP DURING THIS TIME. THIS MEANS THAT LITTLE DRY AIR WILL MAKE IT INTO THE AREA. WITH HIGHER DEWPOINTS AND THE UPPER-LEVEL TROUGH BUILDING OVERHEAD...MORE SHOWERS AND THUNDERSTORMS ARE POSSIBLE MAINLY IN THE AFTERNOON AND EVENING. STILL FEEL CONVECTION COVERAGE WILL BE SCATTERED SINCE THE SHEAR WILL BE WEAK AND ANY LIFTING MECHANISM FROM THE BOUNDARY OR TERRAIN CIRCULATION WILL ALSO BE WEAK. HE COLD FRONT WILL STALL OUT OVER THE REGION AND DISSIPATE. MAX TEMPS WILL RANGE FROM THE 70S IN THE MOUNTAINS TO THE MIDDLE AND UPPER 80S ACROSS MOST OTHER LOCATIONS. CONVECTION COVERAGE SHOULD DISSIPATE OVERNIGHT THURSDAY...BUT WITH THE UPPER-LEVEL TROUGH OVERHEAD AN ISOLATED SHOWER OR THUNDERSTORM CANNOT BE RULED OUT...ESPECIALLY ACROSS THE SOUTHEASTERN CWA WHERE MOISTURE WILL BE DEEPEST. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... ILL-DEFINED SURFACE BOUNDARY WILL RETREAT NORTHWARD AS WARM FRONT FOR FRIDAY. SUBSIDENCE ALOFT SHOULD HINDER CONVECTIVE DEVELOPMENT FOR FRIDAY ALONG THIS FRONT ACROSS THE MAJORITY OF THE AREA...ALTHOUGH STRONGER MOISTURE GRADIENT AND VORT MAX ALOFT MAY TRIGGER DEVELOPMENT TOWARD SOUTHERN MARYLAND...ALONG WITH TERRAIN CIRCULATION CONVECTIVE DEVELOPMENT ACROSS THE POTOMAC HIGHLANDS. MOISTURE ADVECTS ACROSS THE REGION FOR SATURDAY AS HIGH PRESSURE PUSHES OFF THE NORTHEAST COAST. WHILE INSTABILITY INCREASES WITH THIS MOISTURE RETURN...SHORT WAVE RIDGING ALOFT SHOULD LIMIT CONVECTIVE DEVELOPMENT. HOWEVER...CANNOT RULE OUT TERRAIN AND SURFACE HEATING INDUCED AFTERNOON CONVECTION AT THIS TIME AND HAVE LEFT POPS IN THE FORECAST. AS CLOSED CANADIAN LOW DIVES SOUTH OVER THE GREAT LAKES...WESTERLY FLOW ALOFT INCREASES SUNDAY AND MONDAY. SHORT WAVES IN THIS FLOW WILL BRING BETTER CHANCES FOR ORGANIZED CONVECTION TO PUSH THROUGH SUNDAY AND MONDAY AHEAD OF SYNOPTIC COLD FRONT. A MORE COMFORTABLE AIRMASS LOOKS TO ADVECT INTO THE REGION FOR MID WEEK. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... A COLD FRONT WILL MOVE INTO THE AREA TONIGHT AND IT WILL STALL OUT AND WEAKEN THURSDAY THROUGH THURSDAY NIGHT. A LIGHT NORTHERLY FLOW IS EXPECTED BEHIND THE FRONT LATE TONIGHT INTO THURSDAY MORNING...BUT WINDS WILL TURN TOWARD THE SOUTHEAST LATER THURSDAY AND SPEEDS WILL REMAIN LIGHT. SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED THURSDAY AFTERNOON AND EVENING. PATCHY FOG IS POSSIBLE LATE TONIGHT INTO EARLY THURSDAY. MVFR VSBYS ARE EXPECTED DURING THIS TIME...BUT IFR CONDITIONS CANNOT BE RULED OUT ESPECIALLY ACROSS KMRB AND KCHO. MORE FOG IS POSSIBLE THURSDAY NIGHT INTO FRIDAY MORNING. A STALLED FRONT AND SURFACE TROUGH WILL BRING CHANCES OF AFTERNOON STORMS TO THE REGION FRIDAY AND SATURDAY. AN APPROACHING COLD FRONT WILL BRING A BETTER CHANCE OF MORE WIDESPREAD STORMS SUNDAY AND MONDAY. && .MARINE... WINDS WILL SHIFT TO THE NORTH LATE TONIGHT INTO THURSDAY BEFORE GRADUALLY TURNING TOWARD THE SOUTHEAST THURSDAY AFTERNOON. SPEEDS SHOULD REMAIN BELOW SCA CRITERIA. SHOWERS AND THUNDERSTORMS ARE POSSIBLE...ESPECIALLY THIS AFTERNOON AND EVENING...AND AGAIN THURSDAY AFTERNOON AND EVENING. THUNDERSTORMS MAY CONTAIN GUSTY WINDS AND HAIL. A STALLED FRONT AND SURFACE TROUGH WILL BRING CHANCES OF AFTERNOON STORMS TO THE REGION FRIDAY AND SATURDAY. AN APPROACHING COLD FRONT WILL BRING A BETTER CHANCE OF MORE WIDESPREAD STORMS SUNDAY AND MONDAY. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ UPDATE...GMS PREV DISCUSSION...BJL/AEB

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