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/...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.

&&

.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/...

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.

&&

.MARINE...
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.

&&

.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...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 4 AM EDT MONDAY FOR ANZ530>534-
     537>543.

&&

$$
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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