Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 291413 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1013 AM EDT WED APR 29 2015 .SYNOPSIS... HIGH PRESSURE WILL BUILD INTO THE AREA THROUGH WEDNESDAY. LOW PRESSURE WILL IMPACT THE REGION THURSDAY AND FRIDAY. HIGH PRESSURE WILL RETURN FOR THE WEEKEND BEFORE MOVING OFFSHORE EARLY NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... HIGH PRESSURE OVER THE MID-ATLANTIC LATE THIS MORNING. SUBSIDENCE HAS FOSTERED CLEAR SKIES AND QUICKLY RISING TEMPS UNDER FULL SUN. 09Z SREF AND 06Z NAM/GFS INDICATE LOW PRESSURE DEVELOPS IN THE VICINITY OF NYC THIS AFTERNOON...WITH A WEAK BOUNDARY TRAILING BACK TO THE APPALACHIANS. IN SPITE OF DAYTIME HEATING...DEW POINTS INITIALIZING IN THE UPPER 30S AND LOWER 40S WILL LIMIT INSTABILITY. MODELS ARE SUPPORTING POTENTIAL SHOWER AND MAYBE ISOLATED TSTM DEVELOPMENT OVER THE MOUNTAINS...LIKELY DUE TO LOW LEVEL CONVERGENCE GENERATED BY THE BOUNDARY AND TERRAIN CIRCULATIONS. SPC HAS PLACED THE AREA IN THE GENERAL THUNDERSTORM OUTLOOK. OTHERWISE DRY WX EXPECTED WITH CLOUDS INCREASING FROM SW TO NE. HIGH TEMPS HAVE BEEN INCREASED...GOING SLIGHTLY ABOVE AFTERNOON LAMP TEMP GUIDANCE. HIGHS EXPECTED TO BE IN THE MID 70S FROM DC METRO TO FREDERICKSBURG AND LOWER 70S MOST OTHER AREAS. PORTIONS OF THE HIGHLANDS AND THE CENTRAL SHENANDOAH VALLEY...WHERE CLOUD COVER WILL HAVE MORE INFLUENCE...MAY MAX IN THE UPPER 60S. HEADING INTO THE NIGHTTIME HRS...AN UPPER VORT WILL SHOOT DOWN ACROSS THE GREAT LAKES AND QUICKLY INTO THE UPPER MIDWEST - DEEPENING ALL ALONG THE WAY. THE SRN STREAM PIECE OF THIS WAVE WILL BUMP THE SHORTWAVE AND ASSOCIATED RAIN ACTIVITY OFF THE SRN ATLC COAST INSTEAD OF AFFECTING OUR AREA. AREAS OF CONCENTRATED LIFT AND TERRAIN INTERACTIONS W/ THE APLCNS/BLUE RIDGE WILL BEGIN TO OCCUR OVERNIGHT...DEVELOPING SOME SPOTTY SHOWERS THAT WILL INCREASE IN COVERAGE INTO EARLY THU. OVERNIGHT LOWS WILL BE MORE MODERATED W/ THE INCREASE IN CLOUD COVER ACROSS THE AREA...ONLY U40S/L50S FOR MUCH OF THE AREA. && .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/... A POTENT UPPER-LEVEL LOW ASSOCIATED WITH THE NORTHERN BRANCH OF THE JET WILL DROP SOUTH THROUGH THE OHIO VALLEY THURSDAY AND INTO NORTH CAROLINA THURSDAY NIGHT. COASTAL LOW PRESSURE IN THE SOUTHERN BRANCH OF THE JET WILL TRACK NORTHEAST JUST OFF THE NORTH CAROLINA COAST THURSDAY BEFORE MOVING OUT TO SEA THURSDAY THURSDAY NIGHT. THESE TWO SYSTEMS ARE NOT EXPECTED TO PHASE IN TIME...BUT UPPER- LEVEL LOW IN THE NORTHERN BRANCH WILL BE STRONG ENOUGH TO BRING UNSETTLED CONDITIONS TO OUR AREA. AS THE UPPER-LEVEL DROPS THROUGH THE OHIO VALLEY THURSDAY...HEIGHT FALLS AND A LIGHT SOUTHEAST FLOW THROUGH THE MID-LEVELS WILL BE ENOUGH FOR SHOWERS TO DEVELOP. THERE MAY EVEN BE A FEW RUMBLES OF THUNDER FROM LOW TOPPED CONVECTION...ESPECIALLY ACROSS THE CENTRAL AND WESTERN PORTIONS OF THE CWA CLOSER TO THE UPPER-LEVEL LOW. PRECIPITATION WILL BE MOST WIDESPREAD IN THE AFTERNOON WHEN INSTABILITY IS MORE PRONOUNCED AND FORCING WILL BE ENHANCED ALONG A SURFACE TROUGH. THE UPPER-LEVEL LOW WILL PASS BY TO THE WEST THURSDAY EVENING BEFORE DROPPING TO OUR SOUTH OVERNIGHT. MORE SHOWERS ARE LIKELY DURING THIS TIME. THERE MAY BE AN AREA WHERE LOCALLY HEAVIER RAIN SETS UP ACROSS THE EASTERN WEST VIRGINIA PANHANDLE SOUTH INTO CENTRAL VIRGINIA. THIS IS WHERE FORCING WILL BE ENHANCED DUE TO A SURFACE TROUGH THAT WILL EXTEND FROM THE DEPARTING COASTAL LOW TOWARD WEAK SURFACE LOW PRESSURE NEAR THE MASON-DIXON LINE THAT WILL BE ASSOCIATED WITH THE UPPER-LEVEL LOW. THE BEST CHANCE FOR THE HEAVIER RAIN WILL BE DURING THE EVENING HOURS SINCE FORCING ALONG THIS TROUGH WILL WEAKEN AS THE UPPER-LEVEL LOW PUSHES OFF TO OUR SOUTH OVERNIGHT. THREAT FOR FLOODING RAIN IS LOW AT THIS TIME SINCE PWATS WILL BE CLOSER TO CLIMO AND 12-HR FFG GUIDANCE REMAINS OVER 2 INCHES ACROSS MOST AREAS WITH A FEW LOCATIONS IN THE POTOMAC HIGHLANDS/BLUE RIDGE MOUNTAINS BETWEEN 1 AND 2 INCHES. WITH PWATS AND INSTABILITY LIMITED...THIS SHOULD PREVENT EXTREMELY HIGH RAINFALL RATES. && .LONG TERM /FRIDAY THROUGH TUESDAY/... THE UPPER-LEVEL LOW WILL PASS BY WELL TO OUR SOUTH FRIDAY...BUT AN UPPER-LEVEL TROUGH WILL REMAIN OVERHEAD. LIMITED INSTABILITY MAY LEAD TO SOME SHOWERS WHILE NORTHERLY WINDS AND MOSTLY CLOUDY SKIES LEAD TO UNSEASONABLY COOL CONDITIONS. SURFACE HIGH PRESSURE WILL BUILD TOWARD THE REGION FRIDAY NIGHT THROUGH SATURDAY FROM THE MIDWEST. THE UPPER-LEVEL TROUGH WILL SLOWLY DEPART DURING THIS TIME. A NORTHWEST FLOW WILL CONTINUE TO CAUSE BELOW NORMAL TEMPS...BUT SATURDAY WILL BE WARMER THAN FRIDAY DUE TO MORE SUNSHINE. LIMITED INSTABILITY MAY BE ENOUGH TO TRIGGER A COUPLE SHOWERS DURING THIS TIME...BUT THE FORECAST HAS BEEN LEFT DRY FOR NOW DUE TO THE INCREASED SUBSIDENCE EXPECTED BEHIND THE DEPARTING TROUGH AND AHEAD OF THE BUILDING HIGH. THE HIGH WILL BUILD OVERHEAD SATURDAY NIGHT BEFORE BUILDING TO OUR SOUTH SUNDAY THROUGH EARLY NEXT WEEK. A RETURN FLOW AROUND THE HIGH WILL ALLOW FOR NOTICEABLY WARMER AND MORE HUMID CONDITIONS DURING THIS TIME. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/... SOLID VFR CONDS TODAY/TONIGHT. HIGH PRES MOVING OVERHEAD W/ INCREASING MID-DECK CLOUD COVER LATE TONIGHT AND SOME SHOWERS OVER THE APLCNS. AN UPPER-LEVEL LOW WILL IMPACT THE TERMINALS THURSDAY THROUGH THURSDAY NIGHT. SHOWERS ARE LIKELY...ESPECIALLY THURSDAY AFTERNOON AND THURSDAY NIGHT. AN ISOLATED THUNDERSTORM CANNOT BE RULED OUT THURSDAY AFTERNOON AND EVENING. SUBVFR CIGS/VSBYS ARE EXPECTED DURING THIS TIME. A FEW SHOWERS MAY HANG AROUND FRIDAY...BUT PRECIPITATION WILL BE AS WIDESPREAD WITH THE UPPER-LEVEL LOW MOVING AWAY FROM THE AREA. MVFR CONDITIONS ARE POSSIBLE DURING THIS TIME. VFR CONDITIONS EXPECTED FRIDAY NIGHT THROUGH SUNDAY AS HIGH PRESSURE BUILDS TOWARD THE AREA. A STRAY SHOWER CANNOT BE RULED OUT...BUT MOST OF THE TIME WILL BE DRY. && .MARINE... LIGHT WINDS EVEN W/ WEAK NLY CHANNELING THIS MRNG AND SLY CHANNELING TONIGHT. HIGH PRES WILL KEEP CONDS QUIET INTO THU. LOW PRESSURE JUST OFF THE NORTH CAROLINA COAST THURSDAY WILL MOVE OUT TO SEA THURSDAY NIGHT. HOWEVER...THIS SYSTEM WILL STRENGTHEN AS IT DOES SO...AND NORTHEAST WINDS AROUND IT WILL INCREASE. A SMALL CRAFT ADVISORY MAY BE NEEDED FOR PORTIONS OF THE WATERS. AN SCA MAY BE NEEDED FOR PORTIONS OF THE WATERS FRIDAY AS WELL. HIGH PRESSURE WILL BUILD TOWARD THE WATERS FRIDAY NIGHT INTO THE WEEKEND. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...BJL NEAR TERM...GMS/KCS SHORT TERM...BJL LONG TERM...BJL AVIATION...BJL/GMS MARINE...BJL/GMS

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