Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 261434 AAA AFDLWX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1034 AM EDT SUN JUL 26 2015 .SYNOPSIS... A WEAK COLD FRONT APPROACHES THE REGION TODAY THEN DISSIPATES TO OUR NORTH TONIGHT INTO MONDAY. HIGH PRESSURE BUILDS INTO THE REGION TUESDAY AND WEDNESDAY. A STRONGER COLD FRONT WILL CROSS THE AREA THURSDAY. && .NEAR TERM /THROUGH TONIGHT/...
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OBS SHOW SFC DEWPOINTS RUNNING 3-4F DEGS HIGHER THAN 24 HRS AGO IN MOST PLACES AND IN SOME CASES UP TO 5F DEGS HIGHER WHILE 850 MB DEWPOINT HAS REMAINED CONSTANT BASED ON 12Z IAD RAOB. MODIFYING 12Z RAOB SHOWS UP TO 1850 J/KG SB AND 1202 K/JG OF SB AND ML CAPE RESPECTIVELY. RAP13 850 MB THETAE SHOWS A MAXIMUM OVER HIGHLAND AND AUGUSTA COUNTIES AT 18Z FOR MOST LIKELY PLACE OF CONVECTIVE INITIATION AND SHIFTING EAST LATER INTO THE BLUE RIDGE MTNS. EXPECT CONVECTION TO SHIFT EAST TOWARD THE CHESAPEAKE BAY IN THE EVENING ON 10-15 KT ESE 0-6KM AVG WINDS. WEAK FLOW IN THE LOWEST 3KM SHOULD PRECLUDE ANY SVR T-STORMS TODAY.
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&& .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/... FRONT STALLS OUT IN AREA ON MONDAY AS IT BEGINS TO DISSIPATE. THE LINGERING BOUNDARY MAY ALLOW STORMS TO REFIRE THROUGH THE DAY BUT FORCING ALOFT WILL WEAKEN AS WE PROGRESS. HIGHS WILL BE A BIT LOWER THAN SUNDAY THANKS TO CLOUDS AND SHOWERS BUT VERY HUMID WITH DEWS NEAR 70. SHOWER/STORM ACTIVITY IS EXPECTED TO DECREASE IN COVERAGE FAIRLY QUICKLY OVERNIGHT MONDAY AS INSTABILITY WANES AND CINH INCREASES WITH LOSS OF DAYTIME HEATING. && .LONG TERM /TUESDAY THROUGH SATURDAY/... TUESDAY AND WEDNESDAY EXPECTED TO HAVE SIMILAR WEATHER CONDITIONS AS MID/UPPER LEVEL RIDGE OVER MIDWEST NUDGES EVER SO SLIGHTLY EASTWARD CLOSER TO OUR AREA LEADING TO H5 HEIGHT RISES AND NORTH TO NORTHWESTERLY FLOW ALOFT. WEAK SURFACE HIGH WILL PERSIST OVER OUR AREA DURING THIS PERIOD...AND WITH CONTINUED AIRMASS MODIFICATION TEMPERATURES WILL INCREASE INTO THE U80S/L90S TUESDAY AND INTO THE L90S OVER A LARGER AREA WEDNESDAY. DEWPOINTS PROGGED TO GENERALLY REMAIN IN THE M/U60S...SO WHILE IT WILL BE HOT...NOT EXPECTING OPPRESSIVE HEAT...AS HEAT INDICES REMAIN AOB 95F. ATTM...HEIGHT RISES COUPLED WITH LACK OF ANY MEANINGFUL LIFTING MECHANISM WILL LIKELY KEEP OUR AREA DRY BOTH DAYS. THOUGH WITH HEAT AND HUMIDITY IN REGION...ITS NOT ENTIRELY IMPOSSIBLE THAT A STRAY SHOWER/STORM COULD DEVELOP WITH TERRAIN CIRCULATIONS TO OUR WEST AND WANDER INTO OUR FAR WESTERN AREAS. CHANCES ARE EXTREMELY LOW THOUGH...SO KEPT OUT OF GRIDS. BY THURSDAY...MID/UPPER FLOW BECOMES MORE ZONAL AS MAIN PIECE OF UPPER LEVEL ENERGY MOVES TO OUR NORTH AND ASSOCIATED COLD FRONT BEGINS TO APPROACH THE REGION FROM THE NORTHWEST. TIMING OF FRONTAL FEATURE WILL BE CRUCIAL IN HELPING DETERMINE HIGH TEMPERATURES AND STORM CHANCES. THERE IS STILL LOTS OF TIME TO IRON OUT THE SPECIFICS...BUT CURRENT THINKING IS THAT FRONT MOVES THROUGH LATE IN THE DAY...WHICH WILL ALLOW TEMPERATURES TO RISE INTO THE L/M90S AHEAD OF THE FRONT. THIS COMBINED WITH DEWPOINTS NEAR 70F...SUGGEST THAT HEAT INDICES COULD APPROACH 100F. STORM CHANCES WILL INCREASE ALONG THE FRONT...BUT OVERALL COVERAGE AND INTENSITY REMAINS UNCLEAR ATTM. BELT OF STRONGER WINDS ALOFT WILL REMAIN TO OUR NORTH...SO EVEN WITH MODERATE INSTABILITY...OVERALL STORM ORGANIZATION COULD BE RATHER MARGINAL. FRIDAY AND SATURDAY...FRONT MOVES THROUGH MOST OF THE AREA BY FRIDAY MORNING...WHICH WILL KNOCK TEMPERATURES BACK INTO THE M/U80S AND DEWPOINTS BACK INTO THE M/L60S. MOST OF THE AREA SHOULD REMAIN DRY BOTH DAYS...THOUGH IF COLD FRONT STALLS CLOSER TO OUR AREA OUR SOUTHERN ZONES COULD SEE SOME SHOWER/STORM ACTIVITY. && .AVIATION /14Z SUNDAY THROUGH THURSDAY/...
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MOSTLY VFR TODAY BUT THUNDERSTORMS DEVELOPING TO THE NORTHWEST THIS AFTERNOON WILL DROP SOUTHEAST THIS EVENING AND MAY PRODUCE REDUCED CIGS AND VIS...PROBABLY MVFR BUT POSSIBLY BRIEF IFR. RISK OF T-STORMS IS LESS MONDAY DUE TO DRIER AIR. VFR CONDITIONS EXPECTED TUESDAY AND WEDNESDAY AS HIGH PRESSURE DOMINATES. STORM CHANCES INCREASE BY THURSDAY AFTERNOON ALONG/NEAR COLD FRONT...WITH SUB-VFR CONDS POSSIBLE NEAR CONVECTIVE ACTIVITY.
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&& .MARINE...
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MAIN CONCERN IS SOUTHERLY CHANNELING AS FRONT SLIDES SOUTHEAST INTO THE AREA TONIGHT AND MONDAY...WITH SCA CONDITIONS EXPECTED TONIGHT AND POSSIBLE ON MONDAY. LIGHTNING STRIKES THE MAIN CONCERN LATE TODAY OR TONIGHT. HIGH PRESSURE OVER THE AREA WILL KEEP WINDS BELOW SCA CRITERIA TUESDAY AND WEDNESDAY. WINDS EXPECTED TO INCREASE TO NEAR SCA CRITERIA LATE WEDNESDAY INTO THURSDAY AS COLD FRONT APPROACHES THE REGION. FRONT WILL ALSO INCREASE THUNDERSTORM CHANCES BY THURSDAY AFTERNOON AND EVENING ALONG THE WATERS.
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&& .TIDES/COASTAL FLOODING... SOUTHERLY FLOW INCREASES THROUGH TODAY...PUSHING ANOMALIES HIGHER AND CAUSING WATER LEVELS TO APPROACH MINOR FLOOD AT A FEW VULNERABLE LOCATIONS...MAINLY FOR TONIGHTS HIGH TIDE CYCLE. LARGELY DISCOUNTING ESTOFS GUIDANCE AT THIS TIME AS IT HAS BEEN RUNNING TOO HIGH /ABOUT HALF A FOOT HIGHER THAN OTHER AVAILABLE GUIDANCE/. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 4 AM EDT MONDAY FOR ANZ530>534- 537>543.
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&& $$ SYNOPSIS...MSE NEAR TERM...LFR SHORT TERM...MSE/RCM LONG TERM...MSE AVIATION...MSE/LFR MARINE...MSE/LFR TIDES/COASTAL FLOODING...

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