Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 020127
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
927 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/...
UPR LOPRES CONTS TO LIFT NEWD THIS EVNG. BROAD/DIFFUSE HIPRES
AFFECTING CWFA ATTM. A RATHER SUBSTANTIAL PATCH OF LOW CLD
STRETCHES FM THE ERN WVA PNHNDL SEWD ACRS VA. BASES/CIGS GNLY
3000-4000 FT. THERE/S NOT MUCH FLOW TO SPEAK OF AT THIS POINT.
DONT REALLY FORSEE THIS AREA MIXING OUT OVNGT...HWVR SUSPECT IT
WONT BE REINFORCED EITHER. INSTEAD...ITLL BE TRAPPED UNDER
SUBSIDENCE INVRSN /EVIDENT IN LWX 00Z RAOB/...PERHAPS LWRG THRU
THE NGT.

AS LONG AS THESE CLDS ARE AROUND...THE FOG THREAT-- AT LEAST DENSE
FOG-- WL BE DELAYED. THATS NOT THE CASE ACRS MD... WHERE SKIES ARE
MOCLR AND FOG HAS ALREADY BEGUN DVLPG. WL BE REVAMPING CLDS/WX
GRIDS TO ACCOUNT FOR GOING TRENDS.

WITH RIDGING IN PLACE THURSDAY...A MIX OF SUN AND CLOUDS ARE
EXPECTED ONCE CLDS 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 /01Z THURSDAY THROUGH MONDAY/...
CIGS HV DROPPED TO MVFR AT MRB. ELSW...VFR PREVAILS FOR NOW. XPCT
FLGT RESTRICTIONS TO DVLP OVNGT DUE BOTH TO LWRG CIGS AS WELL AS
FOG DVLPMNT. TAFS AS OF 00Z PLACING MORE EMPHASIS ON VSBYS...W/
IFR AT CLIMO FAVORED CHO/MRB AND MVFR AT IAD. HWVR...LTST TRENDS
SUGGESTING LOW CIGS MAY BECOME MORE OF A PLAYER. WL MONITOR FOR
PSBL ADJUSTMENTS. EITHER WAY...WE/LL HV IFR CONDS /OR PERHAPS LWR/
IN PLACE FOR START OF MRNG PUSH WEST OF THE HUBS...AND PERHAPS
ENCROACHING ON IAD/DCA/BWI AS WELL.

CONDITIONS WILL IMPROVE TOWARDS THURSDAY MIDDAY AND VFR 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...
LGT WNDS ON THE WATERS TNGT...W/ SPDS BLO 10 KT. WHILE THERE WONT
BE A STRONG DIRECTIONAL PUSH...A NELY COMPONENT TO THE DRIFT WUD
BE PREFERRED.

NE-E FLOW WILL CONTINUE ON THE WATERS 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...
TIDAL ANOMALIES CONTINUE AROUND A FOOT TO 1.25 FT. WE/VE MET THE
MINOR TIDAL INUNDATION THRESHOLD AT PPTM2 AND SLIM2...AND
ANNAPOLIS IS ON PACE TO DO THE SAME. CSTL FLOOD ADVYS IN PLACE FOR
ALL THREE COUNTIES.

BASED ON CURRENT DEPARTURES...AS WELL AS THE SCOPE OF THE TIDE...
SUSPECT THAT BALTIMORE...SW DC...AND ALEXANDRIA WILL ALSO REACH
MINOR /ADVISORY/ CRITERIA...THOUGH DO NOT EXPECT A LONG RESIDENT
FLOOD. HV ADDED TO THE ADVISORY FOR THESE AREAS MIDNIGHT-5AM.

DO NOT SEE BIG CHANGES IN THE WEATHER REGIME THU-FRI. WINDS WILL
MAINLY BE LIGHT /OR LIGHTER/ WITH AN ONSHORE COMPONENT. WHILE
DEPARTURES MAY NOT CONTINUE QUITE AS SHARP AS THEY ARE NOW... DO
THINK THAT THEY WILL REMAIN ELEVATED UNTIL A COLD FRONT CROSSES LT
FRI NGT.

THE OVERNIGHT TIDE WL BE PREFERRED ASTRONOMICALLY...AND WILL
PROVIDE THE BETTER OPPORTUNITY TO THREATEN CRITERIA. DUE TO
UNCERTAINTIES IN TIDE HGT DURING THE DAYTIME CYCLE...WILL NOT BE
EXTENDING ADVYS JUST YET.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...COASTAL FLOOD ADVISORY FROM MIDNIGHT TONIGHT TO 5 AM EDT
     THURSDAY FOR DCZ001.
MD...COASTAL FLOOD ADVISORY UNTIL 4 AM EDT THURSDAY FOR MDZ014-017-
     018.
     COASTAL FLOOD ADVISORY FROM MIDNIGHT TONIGHT TO 5 AM EDT
     THURSDAY FOR MDZ011.
VA...COASTAL FLOOD ADVISORY FROM MIDNIGHT TONIGHT TO 5 AM EDT
     THURSDAY FOR VAZ054.
WV...NONE.
MARINE...NONE.

&&

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






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