FXUS61 KLWX 111417
AFDLWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
917 AM EST FRI DEC 11 2009
.SYNOPSIS...
HIGH PRESSURE 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/...
UPDATE TO CANCEL WIND CHILL ADV ACROSS THE POTOMAC AND ALLEGHENY
HIGHLANDS THIS MRNG. TEMPS CONT TO WARM BUT WIND CHILL VALUES
WILL STILL BE NEAR ZERO DURING THE MID MRNG. MRNG UPDATE WILL BE
COMING SHORTLY.
PREVIOUS DISCUSSION...
CURRENT ANALYSIS SHOWS LOW PRESSURE OVER THE CANADIAN MARITIMES
WHILE A SURFACE HIGH CONTINUES TO BUILD OVER THE TENNESSEE VALLEY.
WEST-NORTHWEST FLOW BETWEEN THESE TWO SYSTEMS WILL BRING COLD
CONDITIONS TODAY DESPITE SUNSHINE. THE PRESSURE GRADIENT WILL
REMAIN STRONG ENOUGH FOR BLUSTERY CONDITIONS WITH WIND GUSTS THIS
AFTERNOON AROUND 30 TO 35 MPH.
DESPITE SUNSHINE AND WESTERLY FLOW...HAVE LEANED TOWARD THE MET
GUIDANCE WHICH IS COOLER THAN THE MAV GUIDANCE. TEMPS ALOFT WILL
REMAIN QUITE COLD DUE TO STRONG COLD ADVECTION...AND DEEP MIXING
WILL ONLY RESULT IN MAX TEMPS IN THE MID TO UPPER 30S AROUND THE
CITIES. MAX TEMPS IN THE HIGHER ELEVATIONS WILL REMAIN IN THE LOW
TO MID 20S.
STRONG MID-LEVEL JET MAX BETWEEN AN UPPER-LEVEL LOW OVER CANADA AND
A MID-LEVEL HIGH OVER THE CARIBBEAN WILL BRING SOME HIGH CLOUDS
TODAY...ESPECIALLY ACROSS THE CENTRAL AND SOUTHERN PORTION OF THE
CWA. WILL STILL CARRY MOSTLY SUNNY WORDING IN THE ZONES THINKING THE
LAYER WILL BE THIN.
&&
.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 /14Z FRIDAY THROUGH TUESDAY/...
VFR CONDITIONS EXPECTED THROUGH TONIGHT. WEST-NORTHWEST WINDS WILL
GUST TO 25-30 KNOTS...ESPECIALLY LATE THIS MORNING AND 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...
THE PRESSURE GRADIENT WILL REMAIN STRONG BETWEEN LOW PRESSURE OVER
THE CANADIAN MARITIMES AND HIGH PRESSURE BUILDING OVER THE TENNESSEE
VALLEY TODAY. THIS WILL RESULT IN HIGH END SCA WINDS WITH GUSTS
AROUND 30 KNOTS...ESPECIALLY LATE THIS MORNING AND AFTERNOON. WINDS
WILL DIMINISH TONIGHT AS HIGH PRESSURE BUILDS OVERHEAD...BUT SCA
CONDITIONS ARE LIKELY ACROSS THE WATERS THIS EVENING...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 LATER THIS MORNING AND AFTERNOON. FUEL
MOISTURE REMAINS HIGH DUE TO THE RECENT SOAKING RAIN AND SHOULD
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
