FXUS61 KLWX 040541
AFDLWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1241 AM EST FRI DEC 4 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
APPALACHIANS BY WEDNESDAY NIGHT.
&&
.NEAR TERM /THROUGH TODAY/...
05Z ANALYSIS CONTINUES TO SHOW 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 SHOWERS /NOW PRIMARILY
SNOW/ ALONG AND WEST OF THE ALLEGHENY FRONT. EAST OF THE BLUE
RIDGE/CATOCTIN MTN...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 ALTOSTRATUS DURING DAY ON FRI...BECOMING OVC MID
LEVEL STRATUS 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 /TONIGHT THROUGH 6 PM 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 EARLY NEXT WEEK.
&&
.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
SURFACE HIGH WILL CONTINUE TO BUILD TOWARDS THE REGION OVERNIGHT.
LIGHT WINDS LATE TONIGHT THROUGH FRIDAY. A SCT/BKN CU DECK WEST OF
THE BLUE RIDGE 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...
CANCELLED THE SMALL CRAFT ADVISORY AS LATE NIGHT NLY SURGE
REMAINING AT OR BELOW 15 KT. HIGH PRESSURE WILL BUILD OVER THE
WATERS THROUGH FRIDAY. 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...NONE.
&&
$$
SYNOPSIS...JEL
NEAR TERM...BAJ/BJL/JEL
SHORT TERM...JEL
LONG TERM...JEL/BAJ
AVIATION...BAJ/BJL/JEL
MARINE...BAJ/BJL/JEL
