Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 011358 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 958 AM EDT MON SEP 1 2014 .SYNOPSIS...
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A BERMUDA HIGH WILL PERSIST THROUGH TUESDAY. A TROUGH WILL PERSIST OVER THE AREA THIS AFTERNOON. A WEAK COLD FRONT WILL CROSS THE AREA TUESDAY NIGHT...FOLLOWED BY HIGH PRESSURE INTO THE WEEKEND.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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12Z KIAD SOUNDING WAS JUICY...PW VALUE OVER 2 INCHES. WATER VAPOR LOOP INDICATES SOME RELATIVELY DRIER AIR PUNCHING INTO THE HIGHLANDS LIKELY TO EXPAND EAST TOWARD THE INTERSTATE 95 CORRIDOR THROUGH THE AFTERNOON. THIS WOULD EXPLAIN WHY RUC/NAM/GFS FORECAST SOUNDINGS AT VARIOUS POINTS SHOW THE PW VALUE DECREASING A BIT BY AFTERNOON. BUT EVEN 1.75" ISN/T BAD FOR THIS TIME OF THE YEAR. MUCH OF THE AREA WILL LIKELY BE DRY THROUGH THE REST OF THE MORNING...SAVE FOR A FEW SHOWERS ACROSS LOWER SOUTHERN AND NORTHEAST MD. A FEW SHOWERS MAY ALSO AFFECT THE HIGHLANDS BY MIDDAY. AM UNCERTAIN ON COVERAGE OF CONVECTION BY THIS AFTERNOON. SHORTWAVE RIDGING AND MID LEVEL DRYING MAY HELP TO INHIBIT COVERAGE...BUT ONE WOULD THINK THAT LOW LEVEL MOISTURE/INSTABILITY AND PRESENCE OF A SURFACE TROUGH/CONVERGENT BOUNDARY SHOULD ALLOW FOR AT LEAST ISOLATED THUNDERSTORMS /MAYBE LOW END SCATTERED/ TO FORM BY MID-AFTERNOON. POPS/WX REFLECT THIS. GIVEN HIGH MOISTURE CONTENT...ANY STORMS THAT FORM MAY PRODUCE HEAVY RAINFALL ALTHOUGH STORM MOTION SHOULD BE SUFFICIENT ENOUGH TO MOVE CONVECTION AND THUS LIMIT FLASH FLOODING POTENTIAL. INSTABILITY MAY ALSO SUPPORT SOME GUSTY WINDS BUT IF SHEAR REMAINS RELATIVELY WEAK THIS SHOULD LIMIT DAMAGING WIND POTENTIAL AS WELL.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... WEAK SFC RIDGING CROSSES THE CENTRAL MID-ATLANTIC TONIGHT INTO TUESDAY...MAKING FOR AN OVERNIGHT/MOST OF TUESDAY REPRIEVE FROM THUNDERSTORMS. WITH THE BERMUDA HIGH IN PLACE...EXPECT TUESDAY TO HAVE THE HIGHEST TEMPERATURE DAY SINCE JULY. MAX TEMPS LOW TO MID 90S ACROSS LOWER ELEVATIONS. TEMPERATURES MAY BE LOWER OUT WEST WHERE ACTIVITY WILL FIRE FIRST AHEAD OF AN APPROACHING WEAK COLD FRONT. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... BEHIND A SHARP AND POTENT UPPER TROUGH AXIS WILL BE LARGE ZONAL FLOW PATTERN ABOVE THE NRN HALF OF THE CONUS DURING THE MIDDLE OF THE CURRENT WEEK. THIS UPPER-LEVEL HIGHWAY OF FAST-MOVING FLOW WILL NOT ONLY TAKE THE TUE TROUGH PASSAGE QUICKLY AWAY FROM THE AREA AND OFF TOWARD NEW ENGLAND...BUT BRING ANOTHER TOWARD THE AREA JUST A COUPLE OF DAYS LATER - ALL THE WAY FROM THE NRN ROCKIES. THE UPPER RIDGE LAID OUT ACROSS THE SRN HALF OF THE CONUS HOWEVER...WILL KEEP THESE LOW PRES SYSTEM PASSES FROM MAKING A RUN TOO FAR SOUTH. THE FRONTAL PASSAGE OF THE TUE/EARLY WED SYSTEM AND THE LATE WEEK ONE WILL LARGELY SKIM THE REGION W/ THE JUST THE RESIDUAL/LEFTOVER EFFECTS OF THE MORE POTENT SYSTEM FURTHER TO THE NORTH. EVEN W/ THE COLD FRONT EXPECTED TO MOVE ACROSS THE AREA LATE TUE W/ MORE SHOWER/TSTM ACTIVITY...THE UPPER DYNAMICS BEHIND THE STRENGTH OF THE FRONT WILL TAKE OFF TO THE NE. THE LEFTOVER BOUNDARY WILL STALL-OUT TO OUR SOUTH AND ALLOW FOR WEAK HIGH PRES TO BUILD IN ACROSS THE MID-ATLC STATES WED INTO THU. ONLY A SLIGHT AIRMASS CHANGE BEHIND THE FRONT WILL PREVENT TEMPS FROM REACHING THE HIGHER LEVELS EXPECTED ON TUE - THAT OF L-M90S. INSTEAD...MUCH OF THE AREA WILL TOP OUT IN THE M80S...W/ U80S DOTTING THE I-95 CORRIDOR AREA AND EAST. SKIES WILL CLEAR OUT AND A LIGHT WNW WIND WILL DOWNSLOPE AND HELP BUMP UP TEMPS A COUPLE MORE DEG. WITH THE STALLED BOUNDARY TO OUR SOUTH TO CLOSE OUT THE WEEK...DAILY DIURNAL SHOWERS/TSTMS WILL BE DEVELOPING ALONG IT - ACROSS THE CAROLINAS AND POSSIBLY UP INTO CNTRL VA...BUT LIKELY JUST SHY OF THE SRN PERIPHERY OF THE CWA. THE NEXT UPPER LEVEL DISTURBANCE WILL BE THE FAST-MOVING SYSTEM COMING OUT OF THE NRN PLAINS AND OVER THE GREAT LAKES REGION TO CLOSE OUT THE WEEK. THE SFC HIGH WILL ROLL OFF THE COAST AND START UP AN ONSHORE FLOW AS THE COLD FRONT APPROACHES. THIS WILL HELP TO START OUR COOL-DOWN FROM THE ABNORMALLY HOT/HUMID CONDITIONS OF THE PAST FEW DAYS. PRECIP CHANCES WILL INCREASE W/ THE FRONTAL PASSAGE ON FRI INTO SAT. && .AVIATION /13Z MONDAY THROUGH FRIDAY/...
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PATCHY LOW CLOUDS SHOULD DISSIPATE BY 14Z AT THE HUBS. OTHERWISE...MUCH OF THE TIME THROUGH MIDDAY SHOULD BE DRY WITH JUST A PASSING SHOWER. CURRENT FORECAST CALLS FOR SCATTERED COVERAGE OF THUNDERSTORMS BY 18-19Z...THUS THE VCTS. THIS MAY BE TOO EARLY...AND AM SOMEWHAT UNCERTAIN ON HOW MUCH COVERAGE WILL BE APPARENT THIS AFTERNOON AS WELL. WILL EVALUATE 12Z GUIDANCE AND LATEST RUNS OF THE HRRR/WRF-ARW AND AMEND AS NECESSARY. COLD FRONT APPROACHES TUESDAY WITH LEADING THUNDERSTORM ENTERING FROM THE WEST LATE IN THE DAY. SKIES WILL CLEAR OUT ON WED...W/ WINDS SHIFTING TOWARD NWLY AND HIGH PRES BUILDING IN FROM THE NORTH. THE HIGH WILL KEEP CONDITIONS QUIET INTO FRI...AS A COLD FRONT APPROACHES FROM THE UPPER MIDWEST. THE FRONT IS EXPECTED TO BRING MORE PRECIP FROM FRI INTO SAT...SAGGING JUST S OF THE AREA FOR THE COMING WEEKEND.
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&& .MARINE...
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MAIN CONCERN OVER THE WATERS WILL BE POTENTIAL FOR A FEW THUNDERSTORMS LATE THIS AFTERNOON AND EVENING...WITH LOW VIS IN HEAVY RAIN AND GUSTY WINDS/WIND SHIFTS. THUNDERSTORMS ALSO POSSIBLE TUESDAY EVENING WITH A COLD FRONT. HIGH PRESSURE WILL BUILD BEHIND A COLD FRONT LATE TUE EVE. THE FRONT WILL DRIFT JUST SOUTH OF THE AREA...TOWARD THE CAROLINAS. THE SFC HIGH WILL LARGELY KEEP WINDS LIGHT INTO THE LATTER HALF OF THE WEEK...MOVING OFF THE COAST BY EARLY FRI - AHEAD OF ANOTHER COLD FRONT. SCA CONDITIONS NOT ANTICIPATED FOR THE MED/LONG RANGES OF THE FORECAST.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...BAJ/BPP NEAR TERM...BAJ/BPP SHORT TERM...BAJ LONG TERM...GMS AVIATION...BAJ/BPP/GMS MARINE...BAJ/BPP/GMS

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