Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 121905 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 305 PM EDT SAT JUL 12 2014 .SYNOPSIS... HIGH PRESSURE CENTERED OVER NEW YORK STATE WILL SHIFT OFFSHORE TONIGHT AND SET UP A RETURN FLOW INTO NEXT WEEK. A COLD FRONT WILL CROSS THE AREA EARLY NEXT WEEK. AN UPPER LEVEL LOW WILL THEN PERSIST OVER THE EASTERN STATES INTO LATE NEXT WEEK. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... AS OF 18Z...1024MB MSLP AT BUOY 44009 IS 1MB HIGHER THAN THE MID-ATLANTIC COAST...WHICH HAS BROUGHT AN ONSHORE FLOW TO THAT COAST AND SLY FLOW TO THE LWX CWA. MODIFIED 12Z KIAD RAOB HAS 2500 J/JG WITH AN 87F/70F INITIAL SFC TEMP/DP (AT 18Z IT WAS 85F/68F). THIS SLIGHT DROP IN DEWPOINTS AND THE CONSIDERABLE CAP AROUND 700 MB HAS GENERALLY KEPT THUNDERSTORMS LIMITED THUS FAR. THE EXCEPTION IS TERRAIN INDUCED CIRCULATIONS THAT ALLOWED THUNDERSTORMS TO CROSS BETWEEN MARTINSBURG WV AND WINCHESTER VA. OTHER BREAKS IN THE CAP ARE EXPECTED...BUT ONLY ISO/SCT COVERAGE THROUGH THE LATE AFTERNOON DUE TO 20 KT OR LESS BULK SHEAR. HEAVY RAIN AND GUSTY WINDS EXPECTED WITH ANY ACTIVITY. TONIGHT..MAINLY DIURNAL DOWNTREND IN COVERAGE THIS EVENING...THOUGH INCREASING SWLY FLOW OVER THE ALLEGHENIES COULD ALLOW LATE EVENING/MIDNIGHT THUNDERSTORM (RE)DEVELOPMENT. MID LEVEL CLOUDS PERSIST...WHICH ALONG WITH RETURN FLOW MAKE FOR A WARM NIGHT...MIN TEMPS MID TO UPR 60S INLAND...LOW 70S URBAN NEAR SHORE. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY/... SUNDAY...HOTTER AND MORE HUMID THAN SATURDAY. EXPECTED GREATER COVERAGE AND STRONGER THUNDERSTORMS. MAX TEMPS AROUND 90F NORTH/WEST/SOUTHWEST OF THE DC METRO...WITH LOW 90S NRN VA AND CENTRAL/SRN MD INCLUDING BALT/WASH METRO. STILL LITTLE SHEAR TO MAINTAIN STORMS...BUT ONCE THE CAP IS BROKEN...EXPECT MULTICELL DEVELOPMENT TO BE MAINTAINED. WEAK COLD FRONT APPROACHES SUNDAY NIGHT WITH SHEAR INCREASING OVERNIGHT AND ALLOWING A NOCTURNAL THUNDERSTORM THREAT. CHC/LIKELY POPS SPREAD IN FROM THE WEST AFTER MIDNIGHT. THE COLD FRONT STALLS OVER THE AREA MONDAY WITH LIKELY POPS FOR THUNDERSTORMS DUE TO STRONG MOISTURE INFLUX FROM BERMUDA HIGH AND FRONTAL BOUNDARY DRIFTING/STALLED OVER THE AREA. SLIGHT RISK FOR AREA IS JUSTIFIED WITH LIFTED INDEX -4 TO -6C. BULK SHEAR IS STILL WEAK...WITH THE THE UPR JET NOT APPROACHING UNTIL EVENING. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... A STALLED FRONT ACROSS EASTERN MARYLAND AND CENTRAL VIRGINIA WILL BECOME THE FOCAL BOUNDARY FOR ANOTHER ROUND OF FREQUENT SHOWERS AND STRONG THUNDERSTORMS EVERYWHERE TUESDAY AND IN THE EASTERN AREAS INTO TUESDAY EVENING. WITH THE MAIN UPPER LEVEL ENERGY PUSH EXPECTED LATER TUESDAY AFTERNOON AND TUESDAY NIGHT...THE INSTABILITY AHEAD OF THE FRONT AND THE UPPER LEVEL WIND ENERGY WILL QUICKLY ALLOW SHOWERS AND THUNDERSTORMS TO DEVELOP ACROSS THE REGION. PRECIPITABLE WATER ESTIMATES OF 1.50 TO 2 INCHES WILL RELATE TO VERY HEAVY RAINFALL WITH ANY ACTIVITY. RELATIVELY STEEP LAPSE RATES COULD TRANSLATE TO DAMAGING WINDS WITH THE STRONGEST THUNDERSTORMS. WIND GUSTS OVER 50 MPH WOULD BE POSSIBLE. TEMPERATURES WILL TOP OUT IN THE UPPER 80S TO NEAR 90 BEFORE THE SHOWERS AND THUNDERSTORMS BECOME FREQUENT. MUCH OF THE SHOWER AND THUNDERSTORM ACTIVITY WILL PUSH TO THE I-95 CORRIDOR...SOUTHERN MARYLAND AND ADJACENT CHESAPEAKE BAY TUESDAY EVENING. MORE STABLE AIR WILL BE USHERED INTO THE REGION FROM THE NORTHWEST AS A RIDGE OF HIGH PRESSURE BUILDS SOUTHEASTWARD. THERE IS A CHANCE OF A SHOWER OR GUSTY THUNDERSTORM WEDNESDAY MORNING IN SOUTHERN MARYLAND OR ACROSS THE CHESAPEAKE BAY AS A COLD FRONT WILL BE SLOW TO MOVE OFFSHORE. ALTHOUGH THERE SHOULDN`T BE AS MANY SHOWERS AND THUNDERSTORMS EARLY WEDNESDAY...ANY OF THEM COULD BRING A BRIEF DOWNPOUR OR A DAMAGING WIND GUST. TEMPERATURES WILL BE 7 TO 10 DEGREES COOLER WEDNESDAY. A PLEASANT NIGHT IS IN STORE WEDNESDAY NIGHT WITH TEMPERATURES NEAR OR SLIGHTLY BELOW NORMAL WITH DRY AIR SETTLING IN FROM THE NORTHWEST. THERE IS A SLIGHT CHANCE OF A FEW RAIN SHOWERS IN THE POTOMAC HIGHLANDS AND SHENANDOAH VALLEY THURSDAY AFTERNOON AND THURSDAY NIGHT AS WE WILL SEE SOME WEAK UPPER LEVEL ENERGY MOVE ACROSS FROM THE WEST AND A SLIGHT ONSHORE AND UPSLOPE FLOW DEVELOP WITH A SURFACE HIGH SITTING JUST OFFSHORE. TEMPERATURES DURING THE DAY AND AT NIGHT WILL BE SLIGHTLY BELOW NORMAL WITH HIGHS IN THE LOWER 80S AND LOWS IN THE UPPER 50S. WE INCREASE THE CHANCE OF SHOWERS AND THUNDERSTORMS FRIDAY AND SATURDAY AS THE HIGH OFFSHORE USHERS IN MORE HUMID AND WARM AIR FROM THE ATLANTIC AND SOUTHEAST AND A CONTINUOUS STREAM OF UPPER LEVEL ENERGY PUSHES IN FROM THE WEST AND SOUTHWEST. TEMPERATURES FRIDAY SHOULD BE SLIGHTLY BELOW NORMAL OR NEAR NORMAL...BUT BY SATURDAY...TEMPERATURES MAY WORK THEIR WAY ABOVE NORMAL. && .AVIATION /19Z SATURDAY THROUGH THURSDAY/... VFR PREVAILS THROUGH THIS EVENING ASIDE FROM POSSIBLE IFR IN ISO/SCT TSRA. FOG LESS LIKELY TONIGHT DUE TO MID-LEVEL CLOUDS AND SLY FLOW. GREATER THUNDERSTORM COVERAGE SUNDAY AND CONTINUES SUNDAY NIGHT. HEAVY SHOWERS AND STRONG THUNDERSTORMS COULD BRING IFR CONDITIONS...PERHAPS LIFR CONDITIONS...TO ANY TERMINAL TUESDAY WITH A CONTINUATION OF THESE CONDITIONS AT MTN...BWI AND DCA TUESDAY NIGHT. ASIDE FROM STRONG WIND GUSTS IN SHOWERS AND THUNDERSTORMS...SOUTHWEST TO WESTERLY WINDS WILL AVERAGE LESS THAN 10 KNOTS WITH GUSTS TO 15 KNOTS TUESDAY BUT SHOULD VEER AROUND TO THE NORTHWEST AND NORTH-NORTHWEST TUESDAY NIGHT WITH FRONTAL PASSAGE. MVFR OR IFR CONDITIONS ARE POSSIBLE FOR MTN AND BWI WEDNESDAY WITH SOME SHOWER AND THUNDERSTORM ACTIVITY IN THE AREA. WINDS WILL BE NORTHWEST WEDNESDAY VEERING AROUND TO THE NORTHEAST LATER WEDNESDAY LESS THAN 10 KNOTS. WINDS MAY BE STRONGER IN SHOWERS AND THUNDERSTORMS EARLY WEDNESDAY AT THE MTN AND BWI TERMINALS. && .MARINE... SLY FLOW 10-15 KT INCREASES TO 20 KT OVER THE MAIN CHANNEL LATE THIS AFTERNOON/THROUGH TONIGHT WITH GUSTS UP TO 22 KT. SCA UP FROM 4PM SATURDAY TO 6AM SUNDAY. ANOTHER SCA LATE SUNDAY AFTERNOON THROUGH SUNDAY EVENING. A COLD FRONT APPROACHES LATE SUNDAY NIGHT THROUGH MONDAY...WITH LIKELY STRONG THUNDERSTORMS BY LATE MONDAY. SECONDARY COLD FRONT TUESDAY WITH MORE STRONG THUNDERSTORM THREATS. NO HAZARD MARINE CONDITIONS EXPECTED TUESDAY THROUGH WEDNESDAY. && .TIDES/COASTAL FLOODING... WATER LEVELS ARE STILL ONLY A COUPLE TENTHS FOOT ABOVE THE ASTRONOMICAL PREDICTION THIS AFTERNOON. THIS ANOMALY WILL INCREASE TO AROUND THREE QUARTERS FOOT AS SOUTHERLY FLOW STRENGTHENS INTO TONIGHT. THIS MODEST INCREASE AND A FULL MOON SOON WILL ALLOW WATER LEVELS TO APPROACH MINOR FLOODING THRESHOLDS AT SENSITIVE SITES LIKE ANNAPOLIS DURING THE PREFERRED SUNDAY MORNING HIGH TIDE. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 6 AM EDT SUNDAY FOR ANZ531-539>541. SMALL CRAFT ADVISORY UNTIL 6 AM EDT SUNDAY FOR ANZ532>534-537- 543. && $$ SYNOPSIS...BAJ NEAR TERM...BAJ SHORT TERM...BAJ LONG TERM...KLW AVIATION...BAJ/KLW MARINE...BAJ/KLW TIDES/COASTAL FLOODING...BAJ

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