Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 300036
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
836 PM EDT MON SEP 29 2014

.SYNOPSIS...
WEAK HIGH PRESSURE WILL BUILD BRIEFLY OVERNIGHT BEFORE A COLD
FRONT SAGS FROM THE NORTHWEST AND BRINGS A CHANCE OF RAIN SHOWERS
OR PERHAPS AN AFTERNOON THUNDERSTORM TUESDAY. HIGH PRESSURE WILL
RETURN LATER IN THE WEEK. ANOTHER COLD FRONT COULD PUSH THROUGH
THE AREA LATE FRIDAY INTO SATURDAY.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
STILL HAVE SOME LIGHT RAIN CRUISING ACROSS THE LOWER CHESAPEAKE
BAY AREA THIS EVENING. A FEW SHOWERS HAVE ALSO BEEN NOTED ACROSS
PARTS OF NORTHERN MD. MEANWHILE SOME MID-LEVEL DRYING IS STARTING
TO BECOME EVIDENT TOWARD THE POTOMAC HIGHLANDS.

TRENDS SUGGEST LINGERING LIGHT RAIN/SHOWERS WILL BE WANING OVER
THE NEXT FEW HOURS...AND MID-LEVEL DRYING WILL ALSO EXPAND EAST
THROUGH THE CWA. THIS SUPPORTS A DRY OVERNIGHT AND AM BECOMING
INCREASINGLY CONCERNED FOR FOG FOR THE OVERNIGHT. LOW LEVEL
MOISTURE WILL REMAIN TRAPPED BENEATH AN INVERSION. EXTENT OF
CLEARING IS SOMEWHAT UNCERTAIN BUT IF SIGNIFICANT CLEARING OCCURS
TONIGHT...THEN DENSE FOG MAY RESULT.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/...
AS HIGH PRESSURE PUSHES OFFSHORE TUESDAY...A SURFACE FRONT AND ITS
UPPER LEVEL SUPPORT WILL NUDGE INTO THE REGION FROM THE NORTHWEST.
THIS FRONT COULD SPAWN A COUPLE OF RAIN SHOWERS AND PERHAPS A
RUMBLE OF THUNDER OR TWO...GIVEN ANY AMPLE SUNSHINE. WE SHOULD
ENCOUNTER MORE SUNSHINE TUESDAY THAN THIS AFTERNOON BEFORE THE
CLOUDS AND SHOWERS ROLL INTO THE REGION. TEMPERATURES SHOULD BE
GENERALLY IN THE UPPER 70S.

MODELS ARE IN AGREEMENT WITH A 500 MB SHORTWAVE PIVOTING NORTH OF
THE AREA TUESDAY NIGHT. ANY SHOWERS OR THUNDERSTORMS SHOULD ABATE
WITH THE LOSS OF HEATING DURING THE EVENING WITH JUST A FEW STRAY
SHOWERS LEFTOVER ALONG THE MASON-DIXON LINE OVERNIGHT.

HIGH PRESSURE WILL NOSE IN FROM THE NORTH DURING THE DAY WEDNESDAY
RESULTING IN A LOW-LEVEL NORTHEASTERLY FETCH...HOLDING IN LOW-LEVEL
MOISTURE AND KEEPING CLOUDS AROUND. A FEW SHOWERS WILL BE POSSIBLE
PARTICULARLY OVER THE HIGHER TERRAIN WHERE UPSLOPE FORCING COULD
PROVIDE ENOUGH LIFT TO SQUEEZE OUT SOME RAIN DURING THE DAY.

TEMPERATURES WILL BE RIGHT AROUND NORMAL THROUGH THE PERIOD...LOWS
IN THE MID-UPPER 50S AND HIGHS 70-75.

SCATTERED SHOWERS WILL DWINDLE QUICKLY AROUND SUNSET WEDNESDAY
EVENING.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
HIGH PRESSURE WILL REMAIN NORTH OF THE AREA THURSDAY BUT SHIFT A BIT
FURTHER EAST. THIS WILL ALLOW WINDS TO BECOME MORE SOUTHEASTERLY
WITH NOT QUITE AS MANY CLOUDS EXPECTED AND PERHAPS A COUPLE DEGREES
WARMER OVER THE WESTERN AREAS AS COMPARED TO WEDNESDAY...BUT STILL
RIGHT AROUND CLIMO NORMS.

CLOUDS INCREASE THURSDAY NIGHT INTO FRIDAY AS A LARGE AND DEEP
TROUGH DIGS INTO THE UPPER MIDWEST...THEN PIVOTS TOWARD THE
MID-ATLANTIC LATE FRIDAY INTO FRIDAY NIGHT. THE UPPER TROUGH WILL
DRIVE SURFACE LOW DEVELOPMENT OVER THE GREAT LAKES WITH A SUBSEQUENT
TRACK INTO SOUTHEASTERN CANADA. THIS SETUP WILL DRAG A SEASONABLY
STRONG COLD FRONT THROUGH THE AREA FRIDAY NIGHT. STRONG FORCING
ASSOCIATED WITH THE TROUGH AS WELL AS A BIT OF A LOW-LEVEL JET AHEAD
OF THE FRONT WILL LIKELY DRIVE A BAND OF SHOWERS...PERHAPS A FEW
EMBEDDED THUNDERSTORMS GIVEN STRONG FORCING IN SPITE OF A LACK OF
APPRECIABLE CAPE. THE 12Z GFS IS QUITE AMPLIFIED /AS IT WAS
YESTERDAY/ SHOWING THE TROUGH TAKING ON A NEGATIVE TILT IN THE UPPER
LEVELS AND A STRONGER LOW-LEVEL JET RESULTING IN STRONGER FORCING
AND MORE WIDESPREAD HEAVIER RAIN PERHAPS ACCOMPANIED BY GUSTY WINDS.
THE 00Z ECMWF IS NOT QUITE AS STRONG SUGGESTING A BIT LESS
WIDESPREAD SHOWERS WITH WEAKER LOW-LEVEL WINDS.

THE FRONT MOVES EAST OF THE AREA SATURDAY USHERING IN A COOLER AND
DRIER AIRMASS FOR THE WEEKEND. ANOTHER STORM SYSTEM MAY APPROACH BY
EARLY NEXT WEEK BUT FORECAST MODELS/ENSEMBLES DISAGREE ON TIMING.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
ALL TERMINALS IN VFR RIGHT NOW...BUT WITH LOW LEVEL MOISTURE
TRAPPED EXPECT SOME FOG FORMATION TO OCCUR TONIGHT AS SOME MID-
LEVEL DRY AIR WORKS IN. EXTENT OF CLEARING IS SOMEWHAT UNCERTAIN
AND WILL ULTIMATELY DETERMINE HOW LOW VIS WILL GO. HAVE HIT
MRB/CHO THE HARDEST WITH 1/2SM...NOT QUITE AS LOW TOWARD THE HUBS.
BUT IF CLEARING WORKS ALL THE WAY EAST THEN VIS 1/2SM OR LESS IS
PLAUSIBLE LATE TONIGHT/EARLY TUESDAY /AND LOW CIGS IN STRATUS/.

VFR CONDITIONS FOR THE REST OF TUESDAY UNTIL SHOWERS PUSH IN FROM
THE NORTHWEST DURING THE AFTERNOON HOURS. CIG/VSBY RESTRICTIONS
PSBL WRN MOST TERMINALS TUE EVE W/ ISO SHWRS/TSTMS. MOD CONFIDENCE
MAINLY VFR WED-THU. WINDS LIGHT E TO NE TUE NIGHT...AND GENERALLY
LESS THAN 10 KTS THROUGH THU. MORE CIG/VSBY RESTRICTIONS PSBL FRI-
FRI NIGHT AS STRONG FRONT APPROACHES.

&&

.MARINE...
WEAK GRADIENT KEEPS WINDS 10 KT OR LESS THROUGH TUESDAY.

LOOKING LESS LIKELY FOR SCA CONDITIONS LATE TUESDAY NIGHT INTO
WEDNESDAY AS GUIDANCE HAS TRENDED WEAKER AND FURTHER OFFSHORE WITH
LOW PRESSURE. SCA CONDITIONS BECOMING INCREASINGLY LIKELY AHEAD OF
A STRONG COLD FRONT FRIDAY...THEN BEHIND THE FRONT SATURDAY.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...KLW
NEAR TERM...BPP/KLW
SHORT TERM...KLW
LONG TERM...DFH
AVIATION...BPP/KLW/DFH
MARINE...BPP/KLW/DFH






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