FXUS61 KLWX 230845
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
345 AM EST WED DEC 23 2009

.SYNOPSIS...
HIGH PRESSURE WILL REMAIN ACROSS THE MID ATLANTIC THROUGH
THURSDAY. A STORM SYSTEM WILL AFFECT THE REGION CHRISTMAS DAY
THROUGH SATURDAY WITH A WINTRY MIX INITIALLY FOLLOWED BY RAIN.
HIGH PRESSURE RETURNS SUNDAY INTO EARLY NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
WITH TEMPS IN 20S MANY AREAS THIS MRNG...PTNL FOR FOR REFREEZING OF 
MELTED SNOW ON ROADWAYS/SIDEWALKS/ETC CONTS. SPS FOR PATCHY ICE TO 
ACCT FOR THIS.

SFC HIPRES CNTRD OVR GRTLKS TDA WITH RDG AXIS NOSING SEWD INTO MID 
ATLC AS UPR LOW DIVES SWD OUT OF NEW ENG. ENHNCD MSTR IN 850-700MB 
LYR CONTS TO BRING 5-10KFT ST/SC DECK OVHD THRU MRNG...BUT GRDLY 
MOVES S AS H8 THERMAL GRAD PUSHES S. DESPITE AMPLE SOLAR 
RADIATION...LLVL CAA SHUD HINDER BNDRY LYR. NAM KEEPS MAXIMA NEAR 
FZG FOR SGFNT PTN OF CWA...BUT MODELS HAVE BEEN OVR ESTIMATING 
SNOWPACKS EFCT...SO TRENDED TWD WARMER MAV MOS. MAXIMA SHUD RANGE 
FROM L30S ALONG MASON-DIXON LINE TO L40S SHENANDOAH VLY.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/...
STRENGTHENING HIPRES CONTS TO WEDGE SWD ALONG E SIDE OF APLCNS TNGT. 
WITH MSTLY CLR SKIES...LGT WND...AND SNOWPACK SUPPORTING STRG 
RADIATIONAL COOLING...TEMPS SHUD BE COLDER THAN PAST SVRL NGTS. 
WITH COLD BIASES IN GUIDANCE SINCE LAST WKNDS STORM...DIDNT UNDERCUT 
GUIDANCE ANY...AND WENT FOR MINIMA IN U10S/L20S...BUT WUD NOT BE TOO 
SURPRISED IF TEMPS FALL COLDER THAN CURRENT FCST.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
UPPER RIDGE REMAINS OVER THE AREA DURING THE DAYTIME THURSDAY...AS 
SURFACE HIGH PRESSURE WEDGES ITSELF SOUTH THROUGH THE MID ATLANTIC. 
CWA SHOULD SEE PLENTY OF SUNSHINE TO START THE DAY...THEN HIGH 
CLOUDS WILL INCREASE DURING THE AFTERNOON.

UPPER RIDGE SHIFTS EAST OFF THE COAST THURSDAY EVENING. HIGH 
PRESSURE REMAINS LOCKED IN PLACE...PROVIDING A COLD AIR DAMMING SET 
UP. EXPECT CLOUDS TO RAPIDLY THICKEN AND LOWER DURING THE NIGHT AS 
WARM ADVECTION IN THE MID AND UPPER LEVELS INTENSIFIES WELL AHEAD OF 
THE LARGE PLAINS STORM. 

MODEL TREND HAS BEEN TO SLOW DOWN THE ONSET OF PRECIPITATION...HOWEVER
AM CAUTIOUS TO BACK OFF TOO MUCH AS THE MODELS SOMETIMES
PRECIPITATE TOO SLOWLY IN SITUATIONS WITH INCREASING WARM
ADVECTION/ISENTROPIC LIFT. MOREOVER...WITH THE LOW LEVEL
NORTHEAST/EAST FLOW...LIGHT PRECIPITATION WILL NOT BE HARD TO COME
BY EVEN OUTSIDE OF THE MORE ORGANIZED AREA OF LIFT /AND QPF/
DEPICTED BY THE MODELS. SO...AM BRINGING IN CHANCES OF
PRECIPITATION A LITTLE FASTER THAN SOME OF THE MODELS THURSDAY
NIGHT. GIVEN THE WARMING ALOFT...SNOW CHANCES APPEAR VERY SMALL
AND WERE NOT INCLUDED IN THE GRIDS. AND WHILE THERE COULD BE A
LITTLE SLEET AT THE ONSET...FREEZING RAIN/DRIZZLE IS MOST LIKELY
WITH THE DAMMED AIR NEAR THE SURFACE.

LARGER SLUG OF LIFT SPREADS EAST ACROSS THE CWA CHRISTMAS DAY 
/FRIDAY/...FOR CATEGORICAL POPS. WITH SUB-FREEZING NEAR SURFACE
AIR...FREEZING RAIN WILL BE THE PRIMARY P-TYPE TO START CHRISTMAS
ACROSS MUCH OF THE CWA. IN DAMMING SITUATIONS...MODELS TEND TO
ERODE NEAR SURFACE COLD AIR TOO SOON. ACKNOWLEDGING THIS
BIAS...HAVE ALLOWED FREEZING RAIN TO CHANGE TO RAIN BY AFTERNOON
ACROSS MOST AREAS EAST OF THE BLUE RIDGE...BUT HAVE CONTINUED
FREEZING RAIN MENTION FOR AREAS WEST OF THE BLUE RIDGE AS COLD AIR
WILL BE TOUGHER TO DISLODGE ACROSS THE SHENANDOAH VALLEY...EASTERN
WEST VIRGINIA PANHANDLE AND WESTERN MARYLAND. THIS IS THE AREA
THAT WILL HAVE THE MOST PROLONGED PERIOD OF FREEZING RAIN AND
ICING THAT MAY LAST INTO EARLY EVENING FRIDAY.

FRIDAY NIGHT...THE PLAINS STORM LIFTS INTO THE MIDWEST...SENDING AN 
OCCLUDED FRONT INTO THE MID ATLANTIC. MEANWHILE...A WAVE OF LOW
PRESSURE DEVELOPS ALONG THE FRONT IN SOUTHERN VIRGINIA AND PASSES
THROUGH THE MID ATLANTIC SATURDAY MORNING. EXPECT PRECIPITATION
FRIDAY NIGHT TO TAPER OFF FROM THE SOUTHWEST TO NORTHEAST ON
SATURDAY AS A DRY SLOT WORKS ACROSS THE AREA. BEFORE IT DOES
THOUGH...CWA MAY EXPERIENCE AROUND AN INCH OF LIQUID...WHICH ALONG
WITH RECENT SNOW MELT...MAY CAUSE MINOR FLOODING PROBLEMS.

PRIMARY P-TYPE OF RAIN SATURDAY WILL MIX WITH/CHANGE TO SNOW ACROSS 
THE WEST AS COLDER AIR ALOFT BEGINS TO MOVE ACROSS THE HIGHLANDS. 
THIS WILL PAVE THE WAY FOR UPSLOPE SNOW SHOWERS SATURDAY NIGHT AND 
SUNDAY.  

STACKED UPPER LOW WINDS UP OPENING UP ON MONDAY AND THEN SWINGING  
ACROSS THE NORTHEAST AND MID ATLANTIC STATES. FLURRIES COULD EXTEND 
EAST OF THE MTNS WITH STRONG SHORTWAVE/VORT ASSOCIATED WITH THE 
TROUGH. UPSLOPE SNOW SHOWERS WILL BE MAINTAINED INTO TUESDAY. 

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
SCT/BKN 5-10KFT SC DECK CONTS THRU MID MRNG...WITH DRIER AREA 
BRINGING GNRLY SKC CONDS FOR AFTN THRU TNGT...VFR CONDS WILL PVL. 
LGT NW WNDS THRU TNGT.

EXPECT CIGS TO RAPIDLY LOWER THURSDAY NIGHT...LIKELY FALLING INTO 
THE IFR/LIFR CATEGORIES BETWEEN 12Z-15Z FRIDAY. SREFS HAS IFR CIGS 
OCCURRING SOONER...09Z-12Z. AS PRECIPITATION BEGINS...VSBYS WILL 
ALSO LIKELY LOWER TO IFR AFT 12Z. INITIAL P-TYPE AT ALL TERMINALS 
EXPECTED TO BE FREEZING RAIN...BUT IS EXPECTED TO CHANGE TO JUST 
RAIN AT THE HUBS 15Z-18Z. ZR LIKELY TO LINGER AT KMRB LONGER. IFR 
CONDITIONS CONTINUE INTO SATURDAY AS LOW PRESSURE MOVES ACROSS THE 
AREA.

&&

.MARINE...
NW WNDS INCR A BIT TDA WITH CAA HELPING TO MIX DOWN 10 TO 15 KT GTS 
BY AFTN. SIMILAR SPEEDS XPCD TNGT. HIPRES KEEPS CONDS DRY THRU THU.

SMALL CRAFT ADVISORY WINDS MAY DEVELOP LATER FRIDAY INTO EARLY 
SATURDAY UNDER A NORTHEAST FLOW...THEN LATER SATURDAY AND SATURDAY 
NIGHT IN A NORTHWEST FLOW WITH LOW PRESSURE MOVING PAST THE WATERS.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...SBK/PELOQUIN
NEAR TERM...SBK
SHORT TERM...SBK
LONG TERM...PELOQUIN
AVIATION...SBK/PELOQUIN
MARINE...SBK/PELOQUIN