FXUS61 KLWX 040842
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
342 AM EST FRI DEC 4 2009

.SYNOPSIS...
HIGH PRESSURE WILL CONTINUE ACROSS THE MIDDLE ATLANTIC TODAY BUT 
WILL SHIFT SLIGHTLY NORTH OVERNIGHT AS A COASTAL LOW PRESSURE SYSTEM 
FORMS ALONG THE EASTERN GULF COAST. THE LOW PRESSURE CENTER WILL 
MOVE OFF CAPE HATTERAS LATE SATURDAY. HIGH PRESSURE BUILDS ACROSS 
THE REGION FOR SUNDAY AND MONDAY. ANOTHER STORM SYSTEM DEVELOPS IN 
THE MISSISSIPPI VALLEY TUESDAY NIGHT AND MOVES WEST OF THE 
APPALACHIANS DURING MID TO LATE NEXT WEEK.
&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
TRAPPED LOW LEVEL MOISTURE ON THE WEST SIDE OF THE APPALACHIANS TO 
CONTINUE CONTRIBUTING CLOUDS AND SOME SNOW SHOWERS WITH UPSLOPE FLOW 
THROUGH THE MORNING HOURS...THOUGH INTENSITY OF ANY PRECIP WILL 
DIMINISH THROUGH THE LATE MORNING HOURS AS WINDS BACK MORE WESTERLY 
AND MOISTURE AVAILABILITY DECREASES.

SURFACE PRESSURE HAS RISEN EACH HOUR FOR THE PAST 24 HOURS AS 
ADVERTISED. LOW LEVEL RIDGE TO CONTINUE BUILDING ACROSS THE MID 
ATLANTIC THROUGH MIDDAY TODAY...UNTIL THE TROUGH DIGGING DOWN THE 
HIGH SECTIONS OF THE GREAT PLAINS LOSES ITS POSITIVE TILT. 
STRENGTHENING JET OVERHEAD TO QUICKLY ADVECT HIGH CLOUDS CURRENTLY 
OVER THE SERN CONUS /AHEAD OF A S/W OVER THE GULF OF MEXICO/ ACROSS 
THE MID ATLANTIC THROUGH THE LATE MORNING HOURS. CLOUD COVER 
THICKENS IN COVERAGE TO MOSTLY CLOUDY AND LOWERS TO UPPER MID LEVELS 
BY THE LATE AFTERNOON. MAX TEMPERATURES AROUND NORMAL TODAY...NEAR 
50F.
&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/...
TONIGHT...S/W FROM GULF PUSHES NE...REACHING THE GULF 
STREAM...TRIGGERING CYCLOGENESIS OFF THE CAROLINA COAST. LOW CLOUD 
COVER TO INCREASE IN THE NEAR SHORE AS A COASTAL FRONT SETS UP.

WESTWARD EXTENSION OF THE S/W /AHEAD OF THE TROUGH AXIS WHICH IS 
BECOMING NEGATIVELY TILTED/ RIDES NE UP THE APPALACHIAN SPINE 
TONIGHT. THINK THE GFS IS TOO AMBITIOUS WITH A TENTH OF AN INCH OF 
PRECIP ALONG THE WESTERN RIDGES PRIOR TO 12Z...HOWEVER SATURATION 
SHOULD BE REACHED PRIOR TO SUNRISE...INITIATING PRECIP SOMETIME IN 
THE EARLY MORNING HOURS /PARTICULARLY FOR SW ZONES/. COLUMN COLD 
ENOUGH FOR SNOW AT HIGHER ELEVATIONS AND EVAPORATIVE COOLING WOULD 
BRING IMMEDIATE LEE OF BLUE RIDGE AND WEST TO ALL LIGHT SNOW BY 
SUNRISE...WENT WITH STRIPE OF RAIN/SNOW MIX EAST /ROUGHLY ALONG LINE 
FROM KIAD TO KOMH/...THEN ALL RAIN THROUGH TONIGHT'S PERIOD EAST OF 
COASTAL FRONT WHICH SHOULD SETUP ALONG THE I-95 CORRIDOR /WHERE SFC 
TEMPERATURES ARE TO BE UPPER 30S/.
&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
RIDGE AXIS HAS SHIFTED TO THE NORTH OF THE CWFA BY EARLY SATURDAY AS 
LOW PRESSURE EMERGES OFF THE SE COAST AND BRUSHES THE OUTER BANKS OF 
NORTH CAROLINA. PRECIP WILL BECOME WIDESPREAD EARLY SATURDAY MORNING 
AND EVENTUALLY TAPER OFF BY LATE SATURDAY EVENING AS HIGH PRESSURE 
BUILDS IN FROM THE WEST. TEMPERATURES ALOFT WILL DEFINITELY BE COLD 
ENOUGH FOR SNOW...BUT LOW LEVEL TEMPS WILL RANGE FROM THE MIDDLE 30S 
IN THE SHENANDOAH VALLEY/WESTERN SUBURBS OF THE METRO AREAS TO LOWER 
40S ACROSS LOWER SOUTHERN MARYLAND. PTYPE SHOULD BE ALL SNOW OR A 
RAIN/SNOW MIX IN THE WARMER LOCATIONS. HIGHEST QPF SHOULD BE ALONG 
THE SW RIDGES AND ACROSS THE SOUTHERN CWFA. QPF TO SNOWFALL RATIOS 
WILL BE HIGHEST IN THE HIGHER TERRAIN. TOTALS IN THE LOWER 
ELEVATIONS WILL DEPEND HEAVILY ON THE AMOUNT OF RAIN MIXING IN AND 
GROUND TEMPS. 

HIGH PRESSURE WILL BUILD ACROSS THE MIDDLE ATLANTIC FOR SUNDAY AND 
MONDAY...BEFORE MOVING OFFSHORE BY TUESDAY. THE NEXT STORM SYSTEM IS 
EXPECTED FOR THE MIDDLE TO LATE PART OF NEXT WEEK.
&&

.AVIATION /09Z FRIDAY THROUGH TUESDAY/...
MID LEVEL CLOUDS NOW STRUGGLING TO CROSS BLUE RIDGE/ CATOCTIN MTN 
WITH SCATTERED CLOUDS OVER THE SHENANDOAH VALLEY. LOWER MID LEVEL 
CLOUDS TO CONTINUE REDUCING THROUGH THE MORNING HOURS AS FLOW 
DIRECTION BECOMES MORE WESTERLY /LESS IDEAL/.

HIGH CLOUDS STREAM ACROSS THE AREA THROUGH MIDDAY...THICKENING AND 
DEEPENING THIS AFTERNOON/EVENING. PRECIP EVENT ASSOCIATED WITH 
DEVELOPING SYSTEM TO BEGIN LATE TONIGHT WITH LIGHT SNOW POSSIBLE 
ALONG AND WEST OF KCHO TO KIAD LINE AND RAIN EAST.

SUB VFR VSBYS/CIGS IN WIDESPREAD SN/RA EXPECTED ON SATURDAY. 
CONDITIONS WILL BEGIN TO IMPROVE SATURDAY EVENING A LOW PRESSURE 
MOVES OFF OF CAPT HATTERAS AND OUT TO SEA. HIGH PRESSURE AND VFR 
CIGS/VSBYS ANTICIPATED FOR THE EARLY WEEK. 
&&

.MARINE...
TONIGHT...DEVELOPING COASTAL SYSTEM OFF THE CAROLINAS VEERS FOR TO 
NELY AND THE MAGNITUDE INCREASES. BEGAN A SMALL CRAFT ADVISORY AT 4 
AM EST FOR ALL WATERS /DID NOT WANT TO MINCE UP THE ZONES SINCE THE 
WINDS WILL OVERSPREAD THE WATERS SATURDAY MORNING/.

LOW PRESSURE MOVES OFF OF CAPE HATTERAS ON SATURDAY. WINDS WILL 
START OUT SLIGHTLY NORTH OF EAST EARLY SATURDAY AND SHIFT AROUND TO 
THE N/NW AS THE LOW CENTER MOVES OFF THE COAST. BUFKIT AND NAM12 DO 
INDICATE SOLID SMALL CRAFT CONDITIONS SATURDAY AND SATURDAY NIGHT. 
THE GRADIENT SHOULD RELAX EARLY ON SUNDAY AS HIGH PRESSURE BUILDS IN 
FROM THE WEST. HAVE CONTINUED THE SMALL CRAFT THROUGH LATE TOMORROW 
NIGHT...BUT COULD SEE SOME LINGERING 18-20 KT GUSTS THROUGH EARLY 
SUNDAY.
&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 4 AM SATURDAY TO 6 AM EST SUNDAY FOR 
     ANZ530>543.

&&

$$
BAJ/LISTEMAA