FXUS61 KLWX 111539
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1039 AM EST FRI DEC 11 2009

.SYNOPSIS...
HIGH PRESSURE OVER THE TENNESSEE VALLEY WILL BUILD EASTWARD OVER
THE MID-ATLANTIC THROUGH TONIGHT...BRINGING COLD AND DRY
CONDITIONS. HIGH PRESSURE WILL MOVE OFF THE COAST SATURDAY...AND
LOW PRESSURE WILL IMPACT THE REGION SUNDAY INTO EARLY NEXT WEEK.
ANOTHER ROUND OF VERY COLD AIR WILL ARRIVE MID-WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
HIPRES WILL CONTINUE TO BUILD IN FROM THE TN VLY. AFTER A COLD
START TO THE DAY...ACTUALLY THE COLDEST LOWS AT DCA/BWI/IAD SINCE
MARCH 5TH EARLIER THIS YR...HIGHS WILL BE ABOUT 10F BELOW NORMAL.
A BRISK WLY WIND AROUND 10-20 MPH WITH GUSTS AROUND 30 MPH/
SLIGHTLY HIGHER ACROSS EXPOSED RIDGE TOPS/ WILL MAKE IT FEEL
BRISK.

ONLY MINOR TWEAKS FOR THIS FCST UPDATE...BUT BIGGEST CHANGE
WAS LOWERING CLD COVER. SKIES WILL BE SUNNY...EXCEPT FOR SCT HI
CLDS ASSOCIATED WITH AN MID-UPPER JET MAX ACROSS SRN PORTIONS OF
THE CWFA.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/...
SURFACE HIGH WILL BUILD OVER THE REGION TONIGHT...BRINGING CLEAR
SKIES. BLUSTERY CONDITIONS ARE EXPECTED THIS EVENING...BUT WINDS
SHOULD DISSIPATE OVERNIGHT AS THE HIGH BUILDS OVERHEAD. HOWEVER...
VERY DRY AIR ALONG WITH CLEAR SKIES AND LIGHT WINDS WILL PROMOTE
RADIATIONAL COOLING OVERNIGHT. HAVE UNDERCUT GUIDANCE A FEW
DEGREES IN FAVORED AREAS FOR RADIATIONAL COOLING. BITTERLY COLD
CONDITIONS ARE EXPECTED OVERNIGHT...WITH MIN TEMPS RANGING FROM THE
SINGLE DIGITS IN THE POTOMAC HIGHLANDS TO THE TEENS IN THE
NORTHERN AND WESTERN SUBURBS OF WASHINGTON/BALTIMORE...WITH MID
20S IN DOWNTOWN WASHINGTON AND BALTIMORE.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
HIPRES BUILDS ACRS FCST AREA SAT MRNG AND MOVES EWD BY SAT AFTN.
INCRG SLY WINDS SAT AFTN MAY AID IN MODEST WARMING INTO LWR 40S
BENEATH ZONAL FLOW ALOFT.

AS HAS BEEN NOTED LAST SVRL DAYS...LOW-AMPLITUDE SHRTWV TROF MOVES
FROM SRN PLNS ACRS LWR MS RVR VLY TWD MID-ATLC RGN SAT NGT.
ISENTROPIC LIFT AHEAD OF APRCHG SYSTEM WILL PROMOTE DVLPMT OF PCPN
LATE SAT NGT ACRS SWRN ZONES. COLD AIR XPCD TO RMN IN PLACE AT
ONSET...WITH ANY PCPN BGNG IN THE FORM OF SNOW.

WITH APRCH OF WAVE...WARM AIR ADVCTN WILL ERODE COLD LYR QUICKLY
LACKING SFC HIPRES TO N. WARM LYR ALOFT SUGGESTS A BRIEF TRANSITION
TO SLEET AND FREEZING RAIN MAINLY IN VLYS W OF BLUE RDG MTNS...
WHERE COLD SFC AIR WILL LINGER.

COASTAL LOPRES DVLPS OFF CAROLINAS AS WAVE NEARS...WITH CVRG OF
PCPN XPCD TO INCR SGFNTLY BY SUN MRNG. HAVE INCRD POPS FROM PREV
FCST INTO CATEGORICAL RANGE THRU SUN. QUICK EXIT OF UPR WAVE
SUGGESTS RAPID DEPARTURE OF COASTAL LOPRES AND PCPN.

MCFARLAND SIGNATURE NOTED IN GFS/ECMWF H5 PLOTS FOR SAT EVE AND
SUN...WHICH SUGGESTS INVASION OF ANOTHER ARCTIC AMS INTO PLNS
STATES MON. ASSOCIATED SHRTWV TROF WILL MOVE ACRS NRN CONUS.

MODERATION OF AMS XPCD MON AND TUE. COASTAL LOPRES XPCD TO FORM
BY TUE AS SRN STREAM WAVE PHASES WITH NRN STREAM TROF. THIS
SYSTEM WILL INCR CHC OF PCPN AHEAD OF CDFNT. GIVEN XPCD WARM AMS...
ANY PCPN WILL BE LIQUID TUE. 

AGGRESSIVE CDFNT MOVES THRU TUE AFTN IN WAKE OF PASSAGE OF SHRTWV
TROF. COLD AND DRY AIR WILL REPLACE MODERATED AMS...WITH BLUSTERY
CONDITIONS CONTG THRU MUCH OF NEXT WEEK. WNWLY LLVL FLOW MAY FUEL
AN EXTENDED PD OF UPSLP SNOW SHOWERS ALONG WRN SLOPES OF ALLEGHENY
FRONT TUE NGT THRU THU.

&&

.AVIATION /15Z FRIDAY THROUGH TUESDAY/...
VFR CONDITIONS THROUGH TONIGHT. ASIDE FROM A FEW HI CLDS ACROSS
SRN TERMINALS...SKC CONDITIONS WILL PREVAIL. WEST WINDS WILL GUST
TO 25-30 KNOTS LATE THIS MRNG INTO AFTERNOON. WINDS WILL DIMINISH
AS HIGH PRESSURE BUILDS OVERHEAD TONIGHT.

HIPRES MOVES ACRS MID-ATLC SAT MRNG. INCRG CLDS SAT NGT...WITH
RAIN XPCD TO IMPACT TERMINALS SUN AMID LWRD CIGS AND VSBYS.

SUB-VFR CIGS AND VSBYS PSBL AGAIN TUE MAINLY AT ERN TERMINALS AS
COASTAL LOPRES IMPACTS RGN. IN WAKE OF SYSTEM...GUSTY WLY WINDS
XPCD.

&&

.MARINE...
WINDS HAVE INCREASED OVER THE LAST FEW HRS IN RESPONSE TO DAYTIME
MIXING. LATEST OBS SHOW GUSTS TO 20 KT BECOMING MORE WIDESPEAD
WITH A FEW GUSTS TO 25 KT. THE TIGHT PRESSURE GRADIENT BETWEEN
THE LOW OVER THE CANADIAN MARITIMES AND HIPRES OVER THE TN VLY
WILL ALLOW FOR GUSTY WINDS 25-30 KT THRU THE DAY. WINDS WILL
GRADUALLY DISSIPATE TNGT AS THE HI BUILDS OVRHD. SCA WILL REMAIN
IN EFFECT FOR ALL WATERS THRU THIS EVNG...THEN ACROSS THE
CHESAPEAKE BAY AND LOWER TIDAL POTOMAC OVERNIGHT.

SMALL CRAFT ADZY CONTS ACRS LWR TIDAL POTOMAC AND SRN PORTIONS OF
MD CHSPK BAY SAT MRNG BFR WINDS WEAKEN AMID BUILDING SFC HIPRES.
PASSAGE OF TWO COASTAL SYSTEMS SUN AND TUE MAY YIELD SMALL CRAFT
ADZY THRESHOLD WINDS AGAIN FOR PORTIONS OF CHSPK BAY AND TIDAL
POTOMAC. VERY STRONG CDFNT MOVES THRU TUE EVE...AND WILL USHER IN
A PROLONGED PD OF WINDY CONDITIONS ON THE WATERS.

&&

.FIRE WEATHER...
RELATIVE HUMIDITIES WILL DROP TO NEAR OR BELOW 30 PERCENT ACROSS
MANY LOCATIONS TODAY...ESPECIALLY IN NORTHERN AND CENTRAL VIRGINIA
AND THE EASTERN PANHANDLE OF WEST VIRGINIA. FREQUENT WIND GUSTS
OF 30 TO 35 MPH ARE EXPECTED THIS AFTERNOON. FUEL MOISTURE REMAINS
HIGH...GREATER THAN 20 PERCENT...DUE TO THE RECENT SOAKING RAIN AND
WILL LIMIT THE FIRE THREAT TODAY. WINDS WILL DIMINISH TONIGHT AS
HIGH PRESSURE BUILDS OVERHEAD. DRY CONDITIONS ARE EXPECTED TO
CONTINUE SATURDAY...BUT WINDS WILL BE MUCH LIGHTER.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 3 AM EST SATURDAY FOR ANZ530>533-
     538>542.
     SMALL CRAFT ADVISORY UNTIL 9 AM EST SATURDAY FOR ANZ534-537-
     543.
     SMALL CRAFT ADVISORY UNTIL 11 PM EST THIS EVENING FOR ANZ535-
     536.

&&

$$
UPDATE...KLEIN
PREV DISC...LASORSA/KRAMAR