Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 011839
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
239 PM EDT WED OCT 1 2014

.SYNOPSIS...
HIGH PRESSURE WILL BUILD OVERHEAD THROUGH THURSDAY. A STRONG COLD
FRONT WILL APPROACH THE AREA FRIDAY BEFORE PASSING THROUGH FRIDAY
NIGHT INTO EARLY SATURDAY. HIGH PRESSURE WILL RETURN FOR THE
WEEKEND...BRINGING DRIER AND NOTICEABLY COOLER CONDITIONS. THE HIGH
WILL MOVE OFFSHORE EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH THURSDAY/...
AN UPPER LEVEL TROUGH WITH A CLOSED LOW ACROSS THE NORTHEAST CONUS WILL
CONTINUE TO MOVE EASTWARD TODAY. VORT MAXES ACROSS WESTERN PA WILL
MOVE IN THE CYCLONIC FLOW ALOFT. AT THE SFC...HIGH PRESSURE ACROSS
NEWFOUNDLAND WILL WEDGE SOUTH INTO THE MID-ATLANTIC.

AN EASTERLY COMPONENT TO THE SFC WIND WILL CONTINUE TO KEEP MARINE
AIR IN PLACE. A MIX OF SUN AND CLOUDS HAVE BEEN OBSERVED AS MIXING
HAS ALLOWED MOISTURE TO BE DISPLACED ALOFT. AREAS RIGHT UP AGAINST
RIDGE LINES INCLUDING THE BLUE RIDGE AND ACROSS THE POTOMAC
HIGHLANDS HAVE BEEN LOCKED INTO THE LOW STRATUS. THESE CONDITIONS
WILL CONTINUE THIS AFTERNOON. FURTHER WEST...SUNSHINE AS ALLOWED A
CU FIELD TO DEVELOP AND ISO-SCT SHOWERS ARE EXPECTED ACROSS THE VA
HIGHLANDS...POTOMAC HIGHLANDS AND SHENANDOAH VALLEY THIS
AFTERNOON. ALL ACTIVITY SHOULD SUBSIDE BY EVENING.

THE UPPER LEVEL LOW WILL MOVE EASTWARD TONIGHT AND UPPER LEVEL
RIDGING WILL TAKE ITS PLACE ACROSS THE REGION. THE WEDGE OF HIGH
PRESSURE AND EASTERLY FLOW WILL CONTINUE INTO
THE EVENING AND THURSDAY MORNING. LOW CLOUDS WILL SPREAD EASTWARD
FROM THE RIDGELINES LATE TONIGHT AND LEAD TO A CLOUDY THURSDAY MORNING
WITH THE EXCEPTION OF I-95 AND EASTWARD. CONFIDENCE IS LOW AS TO
HOW FAR EAST THE STRATUS WILL REACH BUT IT WILL LIKELY TAKE UNTIL
MIDDAY TO MIX OUT THE CLOUDS. PATCHY DRIZZLE AND FOG ARE ALSO POSSIBLE
ESPECIALLY ALONG I-81. DENSE FOG IS POSSIBLE IN VALLEY LOCATIONS
FOR THE THURSDAY MORNING COMMUTE. WITH RIDGING IN PLACE THURSDAY
AFTERNOON...A MIX OF SUN AND CLOUDS ARE EXPECTED ONCE LOW STRATUS
MIX OUT. FURTHER WEST...TERRAIN CIRCULATIONS MAY CAUSE A CU FIELD
TO DEVELOP ACROSS THE VA HIGHLANDS.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
MAIN STORY OF THE PERIOD WILL BE A STRONG COLD FRONT SWINGING
THROUGH THE AREA. A LARGE TROUGH WILL DIG INTO THE UPPER MIDWEST
DURING THE DAY FRIDAY...ASSUMING A NEGATIVE TILT AS IT PIVOTS ACROSS
THE GREAT LAKES/OHIO VALLEY FRIDAY NIGHT. 500 MB LOW CUTS OFF IN THE
PROCESS AND MOVES ROUGHLY FROM CHICAGO EAST TO PITTSBURGH OVERNIGHT.

STRONG AND DEEP LIFT AHEAD OF THIS TROUGH ALONG A SURFACE COLD FRONT
WILL DRIVE A BAND OF SHOWERS MOVING ACROSS THE AREA FROM WEST TO
EAST FRIDAY AFTERNOON AND FRIDAY NIGHT. THE LATEST GUIDANCE HAS
SLOWED THE TIMING OF THE FRONT SOMEWHAT SO MOST OF THE RAIN LOOKS TO
BE OVERNIGHT FRIDAY NIGHT...ESPECIALLY EAST OF THE BLUE RIDGE.

THE OVERNIGHT TIMING OF THE FRONTAL PASSAGE WOULD MEAN LOWER
INSTABILITY LEVELS AND THUS A LOWER CHANCE OF THUNDERSTORMS OVERALL.
HOWEVER THE AFOREMENTIONED LIFT AND STRONG HEIGHT FALLS/COOLING
ALOFT MAY STILL RESULT IN A LINE OF HEAVIER SHOWERS WITH ISOLATED
LIGHTNING STRIKES DESPITE LOW CAPE. NAM/GFS/ECMWF NOW IN BETTER
AGREEMENT WITH THE STRENGTH OF THE SOUTHERLY LOW-LEVEL JET AS WELL
PRECEDING THE COLD FRONT...BUT AGAIN THE OVERNIGHT TIMING WOULD TEND
TO WORK AGAINST MIXING THE MAJORITY OF THIS WIND TO THE SURFACE. ANY
HEAVIER BANDS OF SHOWERS COULD MIX SOME OF THIS WIND DOWN BUT
OVERALL THE SEVERE THREAT APPEARS TOO LOW TO WARRANT A MENTION IN
THE HWO FOR NOW. WILL CONTINUE TO MONITOR.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
THE FRONT PULLS EAST OF THE AREA SATURDAY MORNING LEAVING IN ITS
WAKE A MUCH COOLER AND DRIER AIRMASS OVER THE WEEKEND. AS THE TROUGH
AXIS PIVOTS OVER THE AREA...FAVORABLE TRAJECTORIES FOR UPSLOPE WILL
BE LIKELY WITH SHOWERS POSSIBLE OVER THE WESTERN SLOPES. SOME
SNOWFLAKES MAY BE MIXED IN AS WELL GIVEN 850 MB TEMPS CRASHING TO
BETWEEN 0 AND -2 C SATURDAY NIGHT. SPOTTY FREEZING TEMPERATURES WILL
BE POSSIBLE ALONG THE RIDGES AS WELL OVERNIGHT SATURDAY NIGHT.

THE AIRMASS WILL QUICKLY MODERATE AS HIGH PRESSURE MOVES EAST
RESULTING IN A LOW-LEVEL SOUTHWESTERLY FLOW BY EARLY NEXT WEEK. THE
NEXT STORM SYSTEM AND CHANCE OF RAIN WILL MOVE ACROSS THE AREA FROM
WEST TO EAST MONDAY NIGHT THROUGH TUESDAY.


&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
VFR/MVFR CONDITIONS EXPECTED THROUGH THE AFTERNOON. CONDITIONS
WILL WORSEN THIS EVENING AND OVERNIGHT AS LOW CLOUDS...DRIZZLE AND
PATCHY FOG FORM. IFR CONDITIONS ARE EXPECTED AT MRB/CHO INTO THURS
MORNING. DUE TO THE LACK OF CONFIDENCE AS TO HOW FAR THE LOW
CLOUDS WILL MOVE EASTWARD...MVFR EXPECTED AT IAD BUT IFR CIGS ARE
POSSIBLE. CONDITIONS WILL IMPROVE TOWARDS THURSDAY MIDDAY AND A
VFR/MVFR CONDITIONS EXPECTED THROUGH THURS AFTERNOON.

LOW CIGS/VSBYS TO IFR OR LWR PSBL FRI-SAT AM IN MOIST SOUTHERLY FLOW
10-20 KTS AND GUSTY AHEAD OF STRONG FRONT. LLWS PSBL FRI NIGHT.
MODELS COMING INTO BETTER TIMING/STRENGTH AGREEMENT LENDING TO
MODERATELY HIGH CONFIDENCE DURING THIS TIME. VFR RETURNS SAT PM AND
PERSISTS THROUGH THE WEEKEND...WINDS TURNING WEST 10-20 KTS BEHIND
FRONT.

&&

.MARINE...
NE-E FLOW WILL CONTINUE ON THE WATERS THROUGH THURSDAY. WINDS
10-15 KTS ARE EXPECTED. THE TIGHTER GRADIENT AND THEREFORE
STRONGER GUSTS ARE ACROSS THE OCEAN WATERS. A ISOLATED GUST OF
18-20KTS IS POSSIBLE ACROSS TANGIER SOUND INTO THURSDAY AFTERNOON.

SCA CONDITIONS VERY LIKELY IN SOUTHERLY CHANNELING AHEAD OF STRONG
COLD FRONT FRIDAY. A BAND OF HEAVY SHOWERS WHICH MAY ENHANCE GUSTY
WINDS WILL APPROACH THE WATERS FROM THE WEST FRIDAY NIGHT. THE FRONT
CLEARS THE WATERS SATURDAY WITH GUSTY NORTHWEST FLOW TO SCA LEVELS
POSSIBLE THROUGH THE REMAINDER OF THE WEEKEND.

&&

.TIDES/COASTAL FLOODING...
NE-E WINDS HAVE LED TO ANOMALIES INCREASING TO OVER A FOOT ACROSS
THE WESTERN SHORE OF THE CHESAPEAKE BAY THIS AFTERNOON. A COASTAL
FLOOD ADVISORY HAS BEEN ISSUED FOR ST.MARYS TO ANNE ARUNDEL
COUNTIES TONIGHT. WINDS ARE EXPECTED TO RELAX SOME THIS EVENING
WHICH MAY CAUSE ANOMALIES TO DROP BUT DUE TO THE PREFERRED HIGH
TIDE AND AN ONSHORE COMPONENT TO THE WIND WATER LEVELS WILL LIKELY INCREASE
THIS EVENING AND THEREFORE AN ADVISORY WAS ISSUED. THIS ADVISORY
MAY NEED TO BE EXTENDED TO INCLUDE BALTIMORE AND
DC/ALEXANDRIA/PRINCE GEORGES COUNTIES.


&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...COASTAL FLOOD ADVISORY FROM 6 PM THIS EVENING TO 4 AM EDT
     THURSDAY FOR MDZ014-017-018.
VA...NONE.
WV...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...HAS
NEAR TERM...HAS
SHORT TERM...DFH
LONG TERM...DFH
AVIATION...HAS/DFH
MARINE...HAS/DFH
TIDES/COASTAL FLOODING...HAS






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