Area Forecast Discussion
Issued by NWS Sterling, VA

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KLWX 180759 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 359 AM EDT MON AUG 18 2014 .SYNOPSIS... A BOUNDARY WILL REMAIN STALLED OVER THE REGION THROUGH TONIGHT. LOW PRESSURE OVER THE OHIO VALLEY THIS MORNING WILL PASS THROUGH THE AREA LATER THIS AFTERNOON THROUGH TONIGHT. THE LOW WILL MOVE AWAY FROM THE AREA TUESDAY...BUT THE BOUNDARY WILL REMAIN NEARBY THROUGH THE END OF THE WEEK. && .NEAR TERM /THROUGH TONIGHT/... A BOUNDARY WILL REMAIN STALLED OUT NEAR NORTHERN MARYLAND TODAY THROUGH TONIGHT. A POTENT SHORTWAVE AND ITS ASSOCIATED SURFACE LOW ARE MOVING THROUGH KENTUCKY THIS MORNING. THIS SYSTEM WILL PASS THROUGH CENTRAL VIRGINIA THIS AFTERNOON AND EVENING BEFORE MOVING OFF TO OUR EAST OVERNIGHT. SHOWERS AND PERHAPS A FEW THUNDERSTORMS WILL INCREASE IN COVERAGE ACROSS CENTRAL VIRGINIA INTO THE POTOMAC HIGHLANDS LATER THIS MORNING AND AFTERNOON. A FEW SHOWERS ARE POSSIBLE ACROSS THE WASHINGTON METROPOLITAN AREA...NORTHERN VIRGINIA...EASTERN WEST VIRGINIA AND WESTERN MARYLAND THIS AFTERNOON AS SUBTROPICAL MOISTURE AHEAD OF THE BOUNDARY COMBINES WITH DAYTIME HEATING TO BRING SOME INSTABILITY. HOWEVER...COVERAGE ACROSS THESE AREAS WILL BE SCATTERED. WILL CONTINUE WITH A DRY FORECAST TODAY ACROSS NORTHEASTERN MARYLAND WHERE DEWPOINTS WILL BE A BIT LOWER AND FORCING FROM SHORTWAVE/SURFACE LOW WILL REMAIN TO THE SOUTH. MAX TEMPS WILL RANGE FROM THE 60S AND 70S ACROSS THE POTOMAC HIGHLANDS AND CENTRAL SHENANDOAH VALLEY WHERE CLOUD COVER AND PRECIPITATION WILL BE MOST WIDESPREAD TO THE LOWER AND MIDDLE 80S ACROSS NORTHERN MARYLAND. MORE SHOWERS ARE EXPECTED TONIGHT...ESPECIALLY ACROSS CENTRAL VIRGINIA AND SOUTHERN MARYLAND. COVERAGE MAY DIMINISH LATE TONIGHT AS THE FORCING SLIDES OFF TO OUR EAST WITH THE SHORTWAVE. WITH SUBTROPICAL MOISTURE CAUSING PWATS TO BE AROUND 2 INCHES...THERE IS A THREAT FOR HEAVY RAINFALL THIS AFTERNOON AND TONIGHT. THE BEST CHANCE FOR HEAVY RAIN WILL BE ACROSS CENTRAL VIRGINIA AND SOUTHERN MARYLAND...CLOSER TO THE FORCING FROM THE SHORTWAVE AND SURFACE LOW. HOWEVER...EVEN ACROSS THESE AREAS ANY FLASH FLOOD THREAT FROM HEAVY RAIN SHOULD BE LOCALIZED SINCE INSTABILITY WILL BE LIMITED FROM CLOUD COVER AND 1 HOUR FFG GUIDANCE IS NEAR 3 INCHES. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... THE SURFACE LOW AND SHORTWAVE WILL CONTINUE TO MOVE TO OUR EAST TUESDAY...BUT THE BOUNDARY WILL REMAIN NEARBY ACROSS NORTHERN MARYLAND. SUBTROPICAL MOISTURE AHEAD OF THE BOUNDARY WILL CAUSE A FEW SHOWERS AND THUNDERSTORMS TO DEVELOP. COVERAGE WILL BE MORE SCATTERED SINCE FORCING ALONG THE BOUNDARY WILL BE WEAK. MAX TEMPS WILL RANGE FROM THE 70S IN THE MOUNTAINS TO THE MIDDLE 80S ACROSS MOST OTHER LOCATIONS AND IT WILL FEEL HUMID. WARM AND HUMID CONDITIONS WILL PERSIST TUESDAY NIGHT. A FEW SHOWERS AND THUNDERSTORMS CANNOT BE RULED OUT...ESPECIALLY DURING THE AFTERNOON AND EVENING. MIN TEMPS WILL RANGE FROM THE LOWER 60S IN THE ALLEGHENY HIGHLANDS TO THE UPPER 60S/NEAR 70 IN WASHINGTON AND BALTIMORE. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... AFTER ONE SHORTWAVE SLIPS SOUTH OF THE SRN PERIPHERY OF THE CWA LATE TUE...ANOTHER WILL BE RIGHT ON ITS HEELS BACK ACROSS THE GREAT LAKES REGION. THIS FEATURE IS PROGGED BY LONG RANGE GUIDANCE...INCLUDING THE GFS/EURO AS SLOWLY SLIDING ACROSS OUR REGION THROUGH THE SECOND HALF OF THE WORK WEEK. THIS WAVE IS EXPECTED TO BE LOCKED IN BETWEEN TWO UPPER RIDGES - ONE TO THE NE AND ONE TO THE SW. THE SWRN UPPER RIDGE WILL STRENGTHEN AS IT RETROGRADES BACK FROM THE CARIBBEAN AREAS TO THE GULF COAST REGION AND UP INTO THE LOWER MS VLY. THE BUILDING OF THIS HIGH PRESSURE ZONE BACK TO THE WEST WILL SQUEEZE THE GREAT LAKES UPPER TROUGH DOWN TOWARD THE MID-ATLC. THE OPPOSING HIGH BACK ACROSS SERN CANADA WILL BE WEAKER BUT STILL ACT AS A BLOCKING FORCE FOR THE UPPER TROUGH AS WELL. NOT AN OVERLY IMPRESSIVE MOISTURE FEED INTO THIS INCOMING LOW PRES DISTURBANCE...MAINLY BECAUSE IT WOULD HAVE TO BE FROM ON ONSHORE FLOW FROM THE MID-ATLC ZONE BACK TOWARD THE APLCNS AND INTO THE UPPER MIDWEST. THIS IS NOT A VERY EFFICIENT METHOD OF INFUSING MOISTURE INTO THE SYSTEM UNTIL THE FEATURE WOULD REACH THE NEAR-COASTAL REGION. A GULF FETCH WOULD BE BETTER BUT THE STRONG UPPER RIDGE WILL LIKELY PREVENT SUCH A FEED. INSTEAD...THE INCOMING PRECIP FROM WED INTO FRI IS EXPECTED TO BE A HYBRID SUB-TROPICAL AND CONTINENTAL AIRMASS W/ LOW-TOPPED AND BRIEF CONVECTION /WEAK/ AND ONLY INTERMITTENT PERIODS AND WAVES OF SHOWER ACTIVITY. THERE WILL ALSO BE PERIODS OF TIME WHERE A STEADY AND STABLE ONSHORE FLOW WILL STRATIFORM-OUT WRN INCOMING CONVECTION AND BASICALLY WEDGE-IN PART OF THE AREA W/ DENSE LOW CLOUDS AND SOME SCATTERED/LIGHT SHOWERS. AS THE MOST RECENT RUN OF THE EURO SUGGESTS...THERE MAY BE A REINVIGORATING OF THE TROUGH IS IT ARRIVES OVER THE AREA TOWARD THE END OF THE WEEK. THE EURO AND GFS DIFFER OF THEIR DEPICTIONS HEADING INTO THE WEEKEND...BUT BEFORE THEN - THE EURO DEVELOPS SOME MORE LOCALLY INTENSE BATCHES OF PRECIP ACROSS THE ERN HALF OF THE AREA THU INTO FRI. STILL TOO EARLY TO PRECISELY NAIL-DOWN MUCH MORE THAN LOW-END POPS FOR THIS LATTER PART OF THE FORECAST PERIOD. BRIEF HEAVY RAIN WILL CERTAINLY BE POSSIBLE AND IS EXPECTED FOR A HANDFUL OF AREAS BY THE TIME THE WEEKEND ARRIVES...BUT IN TERMS OF THIS MULTI-DAY PERIOD...MUCH OF OUR AREA WILL REMAIN DRY - OUTSIDE OF HIGH HUMIDITIES IN THE AIR AND A FEW SCATTERED AND ISOLATED SHOWERS/TSTMS. TEMPS EACH DAY WILL BE MODERATED BY THE RELATIVELY HIGHER HUMIDITY LEVELS BUT STILL REACH AT LEAST THE L80S EACH AFTN W/ PERIODS OF MOSTLY CLOUDY SKIES AND INTERMITTENT BREAKS. OVERNIGHT LOWS WILL ALSO BE RELATIVELY WARM SINCE DEWPOINTS WON`T HARDLY BUDGE OUT OF THE U60S DURING THESE FEW DAYS...SO A RELATIVELY LOW DIURNAL SPREAD EACH DAY. && .AVIATION /07Z MONDAY THROUGH FRIDAY/... MVFR VSBYS ARE POSSIBLE EARLY THIS MORNING...ESPECIALLY ACROSS KCHO DUE TO PATCHY BR. SHOWERS WILL INCREASE IN COVERAGE ACROSS KCHO LATER THIS MORNING INTO TONIGHT. SHOWERS WILL BE SCATTERED ACROSS THE REST OF THE TERMINALS DURING THIS TIME. A THUNDERSTORM CANNOT BE RULED OUT DURING THIS TIME. SUBVFR CONDITIONS ARE POSSIBLE IN PRECIPITATION...ESPECIALLY ACROSS KCHO WHERE IT WILL BE MORE WIDESPREAD. LOW CLOUDS WILL MOVE INTO THE TERMINALS TONIGHT WITH IFR CIGS/VSBYS LIKELY. IFR CONDITIONS WILL SLOWLY IMPROVE TUESDAY...BUT A FEW SHOWERS AND THUNDERSTORMS ARE POSSIBLE. AN UPPER-LEVEL DISTURBANCE WILL MOVE DOWN ACROSS THE REGION FROM WED INTO FRI. ONLY A FEW PERIODS OF LIGHT RAIN AND OF A VERY SCATTERED NATURE FROM WED THRU FRI...POSSIBLY INTO THE WEEKEND. CIG HEIGHTS WILL PERIODICALLY DROP INTO MVFR AND LOWER CATEGORIES PERIODICALLY...AS SFC WINDS SHIFT TOWARD MORE OF AN ONSHORE FLOW. THIS MAY LIMIT AFTN/EVE CONVECTION DEVELOPMENT OVER THE AREA AND FROM THE UPPER MIDWEST. && .MARINE... LOW PRESSURE WILL APPROACH THE WATERS TODAY BEFORE PASSING THROUGH TONIGHT AND MOVING OFF TO THE EAST TUESDAY. THE PRESSURE GRADIENT SHOULD BE WEAK ENOUGH FOR WINDS TO REMAIN BELOW SCA CRITERIA...BUT IT MAY BE CLOSE LATE TONIGHT INTO EARLY TUESDAY. SHOWERS AND A FEW THUNDERSTORMS ARE POSSIBLE...ESPECIALLY ACROSS THE MIDDLE PORTION OF THE BAY AND LOWER TIDAL POTOMAC RIVER THIS AFTERNOON AND TONIGHT. SCA CONDITIONS NOT ANTICIPATED THROUGH THE END OF THE WORK WEEK...W/ A LARGELY STABLE PERIOD FOR INCOMING AND DEVELOPING TSTMS NEARLY EACH AFTN/EVE. && .TIDES/COASTAL FLOODING... AN ONSHORE FLOW WILL DEVELOP AS LOW PRESSURE PASSES BY TO OUR SOUTH LATER TODAY THROUGH TONIGHT AND ANOMALIES WILL INCREASE TO AROUND ONE-HALF FOOT ABOVE NORMAL. THIS WILL CAUSE WATER LEVELS TO BE CLOSE TO MINOR FLOODING THRESHOLDS FOR SENSITIVE AREAS LIKE ANNAPOLIS DURING THE HIGH TIDE CYCLE LATE TONIGHT INTO EARLY TUESDAY MORNING. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL/GMS LONG TERM...GMS AVIATION...BJL/GMS MARINE...BJL/GMS TIDES/COASTAL FLOODING...BJL

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.