FXUS61 KLWX 040213
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
913 PM EST THU DEC 3 2009

.SYNOPSIS...
HIGH PRESSURE WILL BUILD INTO THE MID ATLANTIC FROM THE OHIO
VALLEY THROUGH FRIDAY. ON FRIDAY NIGHT...A LARGE AREA OF LOW
PRESSURE WILL DEVELOP IN THE GULF OF MEXICO...THEN MOVE OFF CAPE
HATTERAS SATURDAY AFTERNOON. HIGH PRESSURE RETURNS TO THE REGION
ON SUNDAY THROUGH MONDAY. ANOTHER STORM SYSTEM DEVELOPS IN THE
MISSISSIPPI VALLEY TUESDAY NIGHT AND MOVES WEST OF THE
APPALACHAINS BY WEDNESDAY NIGHT.

&&

.NEAR TERM /THROUGH FRIDAY/...
CURRENT ANALYSIS THIS EVENING SHOWS SURFACE HIGH BUILDING OVER THE 
PLAINS. THE SURFACE RIDGE AXIS EXTENDS EASTWARD INTO THE OHIO 
VALLEY. A MID-LEVEL TROUGH OF LOW PRESSURE IS LOCATED OVER THE 
CENTRAL PART OF THE NATION WHILE AN UPPER-LEVEL DISTURBANCE ROTATES 
AROUND THIS TROUGH TOWARD THE SOUTHERN ROCKIES. 

THE SURFACE RIDGE WILL CONTINUE TO BUILD EASTWARD INTO THE 
MID-ATLANTIC OVERNIGHT BRINGING DRY CONDITIONS ACROSS MOST OF THE 
CWA. HOWEVER...LOW-LEVEL MOISTURE REMAINS TRAPPED UNDERNEATH THE 
SUBSIDENCE INVERSION...AND THIS WILL RESULT IN A BKN STRATO CU DECK 
ACROSS THE WESTERN CWA ALONG WITH UPSLOPE RAIN/SNOW SHOWERS ALONG 
AND WEST OF THE ALLEGHENY FRONT. FURTHER EAST...A DOWNSLOPING 
WESTERLY FLOW WILL ALLOW FOR MOSTLY CLEAR/PARTLY CLOUDY SKIES. 

RIGHT REAR QUAD OF POLAR JET WILL BE CLOSE ENOUGH IN PROXIMITY TO
HAVE SCT-BKN CIRRUS DURING DAY ON FRI...BECOMING OVC CIRRUS BY 
SUNSET FRI. THE LOW-LEVEL FLOW WILL LIKELY BACK TO THE SOUTHWEST 
DURING THE DAY FRIDAY. THE SOUTHWEST FLOW WILL BRING INCREASING 
AMOUNTS OF MOISTURE...RESULTING IN A SCT TO BKN CU DECK BY THE 
AFTERNOON. BOTH TONIGHT AND FRIDAY SHOULD HAVE SLIGHTLY ABOVE NORMAL 
MINS AND MAXS RESPECTIVELY.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY/...
THERE IS A CHC OF PCPN IN THE SOUTHWEST PORTION OF THE CWA LATE
FRIDAY NIGHT THAT WOULD FALL AS A RAIN/SNOW MIX TO START. 

INCREASING POPS TO LIKELIES PRETTY MUCH THROUGH THE ENTIRE CWA FOR
SATURDAY...WITH A SOUTHWEST TO NORTHEAST PROGRESSION.  

PTYPE AS USUAL IS AN ISSUE.  THICKNESS ANALYSIS DURING THIS PERIOD
FOR 850-700MB IS STRAIGHTFORWARD...WITH THE 1540 DM LINE WELL
SOUTHEAST OF THE REGION...SO PLENTY COLD AIR AOA 850 MB. THIS
ALONE WOULD SUPPORT SNOW BUT THE 1000-850MB THICKNESS IS A BIT
MORE CHALLENGING. LOOKING AT 1290 DM FOR A HIGH CONFIDENCE PTYPE
FORECAST IN THIS LAYER....AREAS WEST OF I-81 FALL IN THIS CATEGORY.
ELSEWHERE AROUND THE REGION...1000-850MB THICKNESS VALUES ARE
MARGINAL BUT BY THE END OF THE DAY...ALL THICKNESS INDICATORS
WOULD SUPPORT SNOW FOR THE ENTIRE REGION.

SO PULLING IT ALL TOGETHER...THERE WILL LIKELY BE A SNOWFALL
EVENT IN THE CWA STARTING SAT MORNING AND LASTING THROUGH EARLY
SAT EVENING. TOO SOON FOR AMOUNTS ATTM...BUT WOULD HAVE TO PUT IT
AT THIS TIME ON THE LIGHT SIDE.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
SUNDAY WILL BE PLEASANT WITH HIGH PRESSURE BUILDING. ANOTHER
STORM SYSTEM WILL DEVELOP IN THE LOWER MISSISSIPPI VALLEY AND
TRACK TO THE ST. LAWRENCE VALLEY...GIVING US THE POTL CHANCE FOR
ANOTHER RAIN EVENT SIMILAR TO LAST NIGHTS.

&&

.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
SURFACE HIGH WILL CONTINUE TO BUILD TOWARDS THE REGION OVERNIGHT. 
WIND GUSTS 10-15 KNOTS THIS EVENING WILL DIMINISH OVERNIGHT. LIGHT 
WINDS ARE EXPECTED LATE TONIGHT THROUGH FRIDAY. A SCT/BKN CU DECK 
ACROSS THE WESTERN TERMINALS WILL REMAIN ABOVE 3KFT OVERNIGHT. 

HIGH CLOUDS WILL INCREASE FRIDAY AS AN UPPER-LEVEL DISTURBANCE 
APPROACHES FROM THE SOUTHWEST. A SCT/BKN CU DECK WILL DEVELOP DURING 
THE AFTERNOON ACROSS ALL OF THE TERMINALS. CIGS MAY APPROACH MVFR 
LEVELS BY LATE IN THE DAY. 

&&

.MARINE...
WILL CONTINUE WITH A SMALL CRAFT ADVISORY UNTIL 4 AM FOR THE 
CHESAPEAKE BAY FROM SANDY POINT TO SMITH POINT AND FOR THE LOWER 
TIDAL POTOMAC. NORTH-NORTHWEST WINDS WILL CHANNEL DOWN THE BAY AND  
LOWER TIDAL POTOMAC. HIGH PRESSURE WILL BUILD OVER THE WATERS BY 
FRIDAY MORNING. WINDS WILL REMAIN BELOW SCA CRITERIA FRIDAY. SMALL  
CRAFT CONDITIONS AGAIN LIKELY ON SATURDAY WITH A NE BLOW.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 4 AM EST FRIDAY FOR ANZ532>534-537-
     540-541-543.

&&

$$
SYNOPSIS...JEL
NEAR TERM...BJL/JEL
SHORT TERM...JEL
LONG TERM...JEL
AVIATION...BJL/JEL
MARINE...BJL/JEL