Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 201856 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 256 PM EDT WED AUG 20 2014 .SYNOPSIS... A STATIONARY BOUNDARY WILL REMAIN OVER THE REGION THROUGH THURSDAY. THE BOUNDARY WILL SLOWLY DROP SOUTH AND WEST AS A COLD FRONT FRIDAY AND HIGH PRESSURE OVER NEW ENGLAND WILL EXTEND INTO OUR AREA FOR THE WEEKEND. HOWEVER...UNSETTLED CONDITIONS MAY PERSIST DURING THIS TIME DUE TO PLENTY OF MOISTURE FROM THE ATLANTIC. && .NEAR TERM /THROUGH THURSDAY/... AN UPPER LEVEL TROUGH IS LOCATED ACROSS THE GREAT LAKES WHILE MULTIPLE DISTURBANCES MOVE ACROSS THE MID WEST IN NORTHWEST FLOW ALOFT. A JET STREAK IS ROUNDING THE BASE OF THE TROUGH ACROSS THE GREAT LAKES AND OHIO VALLEY. A WEAKENING SHORTWAVE TROUGH WILL CONTINUE TO MOVE ACROSS THE ALLEGHENY FRONT THIS AFTERNOON WHILE SHOWERS AND THUNDERSTORMS MOVE EASTWARD ACROSS THE POTOMAC HIGHLANDS...SHENANDOAH VALLEY AND NORTHERN VA. MESOSCALE ANALYSIS SHOWS 500-1000 J/KG WEST OF I-95 AND 25-30KTS OF SHEAR. PWATS HAVE RISEN TO 1.6-1.8 INCHES ACROSS THIS REGION. AN ISOLATED SEVERE THREAT WILL CONTINUE THIS AFTERNOON WITH DMG WINDS AS THE MAIN THREAT. BOWING SEGMENTS AND RIJ SIGNITURES HAVE BEEN OBSERVED ON RADAR. AT THIS TIME...HAVE NOT CONFIRMED GROUND TRUTH REPORTS FOR DMG WINDS. HEAVY RAINFALL HAS ALSO BEEN OBSERVED. HRRR INCREASES COVERAGE OF SHOWERS AND THUNDERSTORMS AND ACTIVITY SHOULD REACH THE I-95 LATE THIS AFTERNOON AND EARLY EVENING. SHOWERS AND THUNDERSTORMS WILL DECREASE IN COVERAGE THIS EVENING. SOUTHERLY FLOW AT THE SFC WILL KEEP MOIST CONDITIONS ACROSS THE MID ATLANTIC. PATCHY FOG IS POSSIBLE ACROSS THE REGION MAINLY IN VALLEY LOCATIONS AND LOCATIONS THAT RECEIVED RAIN TODAY. THE UPPER LEVEL TROUGH WILL MOVE ACROSS ONTARIO BY THURSDAY MORNING AS A RIDGE BUILDS INTO THE CENTRAL PLAINS. MULTIPLE DISTURBANCES ARE EXPECTED TO MOVE ACROSS THE MID WEST BUT TIMING IS DIFFICULT. A SFC TROUGH IS EXPECTED ACROSS THE REGION THURSDAY. THIS WILL PRODUCE WESTERLY WINDS BEHIND THE TROUGH AND SOUTHERLY FLOW AHEAD OF THE TROUGH. AT THIS TIME...A DISTURBANCE IS EXPECTED TO APPROACH THE REGION THURS AFTERNOON FROM THE NORTHWEST. SHOWERS AND THUNDERSTORMS WILL MOVE INTO THE REGION AT THIS TIME AND MOVE EAST-SOUTHEAST. THE SFC TROUGH WILL ALSO LEAD TO ISOLATED DEVELOPMENT IN THE AFTERNOON. AT THIS TIME...INSTABILITY WILL BE MARGINAL AND SHEAR SEEMS WEAK. ACTIVITY SHOULD BE SUB-SEVERE. PWATS ARE EXPECTED TO RISE NEAR 1.9 INCHES THURSDAY PRODUCING HUMID CONDITIONS. SHOWERS AND THUNDERSTORMS WILL BE CAPABLE OF PRODUCING HEAVY RAIN. && .SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY/... THE CHANCE OF SHOWERS AND THUNDERSTORMS WILL CONTINUE THURSDAY NIGHT AND INTO FRIDAY AS A 250MB JET SITS NEAR THE REGION AND DISTURBANCES APPROACH FROM THE GREAT LAKES. SUBSIDENCE BEHIND THE DEPARTING DISTURBANCES MAY LEAD TO CLEARING FRIDAY AND THEREFORE INSTABILITY WILL LIKELY INCREASE. AT THIS TIME...CONFIDENCE IS LOW ON THE TIMING OF SHOWERS AND THUNDERSTORMS. FCST MAX TEMPS WILL REACH THE LOW 80S ON FRIDAY. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... A WEAK WAVE OF LOW PRESSURE FOCUSED IN THE MID AND UPPER LEVELS WILL CROSS THE AREA OVERNIGHT FRIDAY...PROVIDING ONE FINAL PERIOD OF ENHANCED RAINFALL AS A BACKDOOR COLD FRONT MOVES THROUGH AT THE SURFACE. A SUBTROPICAL RIDGE WILL BUILD OVER THE EASTERN US FOR WEEKEND AS SURFACE HIGH PRESSURE CENTERED OVER THE NORTHEASTERN US RIDGES DOWN THE EASTERN SEABOARD. THIS RIDGING COMBINED WITH EASTERLY FLOW AROUND THE NORTH SIDE OF A COASTAL LOW OFF OF CAPE HATTERAS WILL BRING ONSHORE FLOW FOR THE MID-ATLANTIC MIDDAY SATURDAY THROUGH THE BEGINNING OF NEXT WORKWEEK. THE MARINE LAYER THAT WILL FILL IN WILL BRING SEASONABLY COOL AND MOIST AIR...LEADING TO A LOW CLOUD DECK THAT WILL HANG AROUND THROUGH THE WEEKEND AND LIKELY INTO MONDAY EVENING...PARTICULARLY EAST OF THE BLUE RIDGE. CHANCE POPS WILL REMAIN IN THE FORECAST ALONG AND WEST OF THE BLUE RIDGE WHERE THERE WILL BE AN UPSLOPE COMPONENT TO THE MOIST EASTERLY FLOW. THE SURFACE HIGH WILL MIGRATE OFF OF THE MID-ATLANTIC COAST MONDAY NIGHT AND SOUTHERLY FLOW WILL BEGIN TO FILL IN LOCALLY. THIS WILL SIGNAL AN INCREASE IN TEMPERATURES AS HIGHS WILL GO FROM THE MID TO UPPER 70S SATURDAY THROUGH MONDAY TO NEAR 80 TUESDAY AND MID 80S WEDNESDAY. NO SIGNIFICANT PRECIPITATION FEATURES ARE EXPECTED THROUGH THE FIRST HALF OF NEXT WEEK. && .AVIATION /19Z WEDNESDAY THROUGH MONDAY/... SHRA AND TSRA IS EXPECTED THIS AFTERNOON AS A LINE OF TSRA MOVES EASTWARD. GUSTY WINDS AND IFR VSBYS POSSIBLE IN TSRA. THIS WILL CONTINUE THIS AFTERNOON. SOUTHERLY FLOW WILL KEEP MOISTURE IN THE REGION OVERNIGHT AND PATCHY IFR VSBYS ARE POSSIBLE AT MRB AND CHO. MVFR VSBYS ARE POSSIBLE AT IAD. MVFR/IFR CIGS ARE POSSIBLE NEAR BWI-MTN BUT CONFIDENCE IS LOW AT THIS TIME. SHRA AND TSRA POSSIBLE THURSDAY AFTERNOON AND INTO FRIDAY AND MAY CAUSE MVFR/IFR RESTRICTIONS. PERIODS OF LOW CEILINGS ARE POSSIBLE AS A MID AND UPPER LEVEL DISTURBANCE CROSSES THE AREA FRIDAY NIGHT AND THEN AGAIN OVER THE WEEKEND AND INTO EARLY NEXT WEEK AS A MARINE AIRMASS SETTLES INTO THE AREA. && .MARINE... SOUTHERLY FLOW WILL CONTINUE ON THE WATERS THROUGH FRIDAY. WINDS SHOULD STAY BELOW SCA CRITERIA. SHOWERS AND THUNDERSTORMS ARE EXPECTED THIS EVENING AND AGAIN THURSDAY AFTERNOON AND NIGHT. SOME THUNDERSTORMS MAY PRODUCE GUSTY WINDS. A SMALL CRAFT ADVISORY MAY BE NECESSARY SATURDAY NIGHT THROUGH SUNDAY NIGHT IN BREEZY EASTERLY FLOW AROUND THE NORTH SIDE OF A COASTAL LOW OFF OF THE NORTH CAROLINA FLOW. && .TIDES/COASTAL FLOODING... AN ONSHORE FLOW WILL CONTINUE THROUGH TONIGHT...BUT IT WILL REMAIN WEAK. THE FLOW MAY TURN MORE TOWARD THE SOUTHEAST WHICH WOULD CAUSE WATER LEVELS TO BE SLIGHTLY HIGHER THAN THEY HAVE BEEN RECENTLY. THIS WILL CAUSE WATER LEVELS TO BE CLOSE TO MINOR FLOODING THRESHOLDS DURING THE HIGH TIDE CYCLE LATE TONIGHT INTO EARLY THURSDAY MORNING. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...HAS NEAR TERM...HAS SHORT TERM...HAS LONG TERM...CEB AVIATION...HAS/CEB MARINE...HAS/CEB TIDES/COASTAL FLOODING...LWX

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