FXUS61 KLWX 070858
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
358 AM EST TUE FEB 7 2012

.SYNOPSIS...
HIGH PRESSURE WEAKENS OVER THE AREA TODAY. LOW PRESSURE WILL
PASS THROUGH THE MID-ATLANTIC REGION WEDNESDAY. HIGH PRESSURE
RETURNS THURSDAY AND FRIDAY. A COLD FRONT MOVING INTO THE REGION
WILL BRING COLDER AIR TO THE MID ATLANTIC FOR THE WEEKEND.

.NEAR TERM /THROUGH TONIGHT/...
MID LEVEL VORT MAX/TROUGH WAS MOVING ACROSS NORTHERN VA/SOUTHERN MD 
OVERNIGHT...WITH SOME CLOUDS AND EVEN A FEW SPRINKLES. THIS FEATURE 
WILL MOVE EAST OF THE CHESAPEAKE BAY REGION BY DAYBREAK AND ANY 
CLOUDS SHOULD HAVE SHIFTED TO THE EAST WITH IT. 

BEHIND THIS FEATURE...EXPECT SUNSHINE TODAY WITH NVA BEHIND THE VORT 
MAX AND A DOWNSLOPING FLOW IN THE LOW LEVELS EAST OF THE MTNS. WILL 
HAVE TO WATCH CLOUDS DIVING SOUTH INTO NORTHERN PENNSYLVANIA AT 08Z 
AS THEY MAY APPROACH THE MASON DIXON LINE DURING THE AFTERNOON 
ALTHOUGH A LOT OF GUIDANCE KEEPS THESE CLOUDS FROM ADVECTING TOO FAR 
SOUTH INTO THE CWA THROUGH TODAY. 

MEANWHILE...A WEAK BACKDOOR FRONT SLIPS SOUTH TOWARD THE MASON
DIXON LINE THIS AFTERNOON AND THEN SOUTH OF THE CWA THIS EVENING
BUT THIS FRONT SHOULD PASS THROUGH DRY. CLOUDS WILL THICKEN AND
LOWER TONIGHT AS THE NEXT SHORTWAVE OVER THE MISSISSIPPI VALLEY
MOVES EAST TOWARD THE TENNESSEE VALLEY. IT LOOKS AS IF MOST OF THE
PRECIP ASSOCIATED WITH THIS WILL HOLD OFF TIL WEDNESDAY.

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
A SHORTWAVE TROUGH WILL PASS THRU THE MID-ATLANTIC STATES ON WED. 
WHILE DYNAMICS AND MOISTURE WITH THIS SYSTEM ARE NOT ALL THAT 
IMPRESSIVE...UPPER DIVG IN LEFT-ENTRANCE REGION OF ULVL JET-STREAK 
AND DPVA AHEAD OF THE VORT MAX WILL PROVIDE SOME FORCING FOR LGT 
PRECIP ON WED. MODELS IN FAIRLY GOOD AGREEMENT WITH TIMING AND QPF. 
HAVE INCREASED POPS TO LIKELY ACROSS MOST OF THE CWA. PRECIP WILL 
LIKELY OVERSPREAD LOCATIONS NEAR AND WEST OF THE BLUE RIDGE DURING 
THE MRNG BEFORE REACHING THE CITIES BY THE MIDDAY/AFTN HRS. 

AS IS OFTEN THE CASE...MODELS DISCREPANCIES RESIDE WITHIN THE 
BOUNDARY-LAYER. PTYPE WILL BE DETERMINED BY TEMPS IN THE BOUNDARY 
LAYER. PREFER A COLDER SOLUTION THAN PREVIOUS FCSTS HAVE INDICATED. 
GIVEN THE DRY AIRMASS ALREADY IN PLACE /DEWPOINTS IN THE 20S/... 
EVAPORATIVE EFFECTS IN THE BOUNDARY LAYER WILL CAUSE BOUNDARY LAYER 
TEMPS TO COOL AS PRECIP REACHES THE GROUND. DESPITE MODEL 
DIFFERENCES IN BOUNDARY-LAYER/SFC TEMPS DURING THE DAY...MOST 
GUIDANCE IN AGREEMENT WITH WET-BULB TEMP PROFILES GENERALLY AT OR 
BELOW FREEZING THRU MOST OF THIS EVENT ACROSS MUCH OF THE ERN WV 
PANHANDLE...NRN MD AND EXTREME NWRN VA. PTYPE WILL LIKELY BE ALL 
SNOW ACROSS THESE AREAS. LGT QPF AND MARGINAL SFC TEMPS WILL LIMIT 
SNOWFALL ACCUMULATIONS...BUT THERE IS A POTENTIAL FOR 1-2 INCHES OF 
SNOW. 

FURTHER SOUTH AND EAST TOWARD THE CITIES/CENTRAL VA/SRN MD...PTYPE 
IS LESS CERTAIN DUE TO THE SLIGHTLY WARMER BOUNDARY LAYER TEMPS. 
HAVE BLANKETED THE AREA WITH RA OR SN. SUBSEQUENT SHIFTS WILL REFINE 
RA-SN LINE AS WE GET CLOSER TO THE EVENT. 

THE TROUGH WILL MOVE OFF THE ERN SEABOARD WED EVE AS HIPRES BUILDS 
IN FROM THE WEST. RA/SN MAY LINGER ACROSS NERN MD DURING THE ERY 
EVE...BUT DID NOT GO HIGHER THAN SLIGHT CHANCE AS PRECIP TENDS TO 
MOVE OUT QUICKER THAN GUIDANCE INDICATES. LGT UPSLOPE SN SHOWERS 
WILL BE POSSIBLE DURING THE EVE ACROSS THE WRN-FACING SLOPES OF THE 
ALLEGHENY FRONT. MIN TEMPS WED NGT WILL BE IN THE 30S ALONG AND EAST 
OF I-95. LOWERED MIN TEMPS A FEW DEGREES TO THE MID 20S ACROSS THE 
ERN PANHANDLE OF WV...EXTREME NWRN VA AND NRN MD...WHERE A LGT SNOW 
PACK IS EXPECTED.

HIPRES WILL CONTINUE TO EXPAND EWD INTO THE MID-ATLANTIC REGION THU 
AND THU NGT. DRY WX IS EXPECTED DURING THIS TIME. MAX TEMPS THU WILL 
RANGE FROM THE UPPER 30S ACROSS THE POTOMAC HIGHLANDS TO NEAR 50F IN 
THE NRN PIEDMONT.

.LONG TERM /FRIDAY THROUGH MONDAY/...
LARGE-SCALE PATTERN CHANGES IN STORE FOR MOST OF THE LONG-TERM 
PERIOD. THE DEVELOPMENT OF AN ALEUTIAN LOW WILL INDUCE DOWNSTREAM 
RIDGE BUILDING OVER WRN NOAM AND TROUGHING OVER ERN NOAM. 
LARGE-SCALE TROUGH ASSOCIATED WITH HUDSON BAY VORTEX WILL AMPLIFY 
LATE THIS WEEK INTO THE WEEKEND. A COLD FRONT WILL MOVE THRU THE 
REGION FRI NGT OR SAT. CANNOT RULE OUT ISO SN SHOWERS WITH FROPA.

BEHIND THE FRONT...AN ARCTIC AIRMASS WILL BECOME MODIFIED BY THE 
TIME IT REACHES THE MID-ATLANTIC REGION AS IT PROGRESSES SWD INTO AN 
AREA WITH LITTLE OR NO SNOW COVER. NONETHELESS...SLIGHTLY BELOW 
NORMAL TEMPS ARE EXPECTED FOR THE WEEKEND. MODERATING TEMPS EXPECTED 
DURING THE ERY TO MID PART OF NEXT WEEK AS THE POLAR VORTEX LIFTS 
NEWD.

.AVIATION /09Z TUESDAY THROUGH SATURDAY/...
SHORTWAVE EXITS BY 10Z THIS MORNING. VFR CONDITIONS EXPECTED
TODAY AS WEAK BACKDOOR FRONT MOVES THROUGH FROM THE NORTH WITH
LITTLE/NO IMPACT THIS EVENING. CLOUDS THICKEN/LOWER OVERNIGHT BUT
SHOULD REMAIN AT VFR LEVELS THROUGH 12Z WED.

AN UPPER TROUGH WILL MOVE THRU THE TERMINALS ON WED. LGT SN IS 
EXPECTED TO IMPACT THE TERMINALS DURING THE DAY...WHICH WOULD LEAD 
TO IFR CIGS AND VSBYS. PRECIP MAY MIX WITH OR CHANGE TO RA AT CHO 
AND POSSIBLY DCA DURING THE AFTN. 

IMPROVING CONDITIONS FROM WEST TO EAST WED EVE AS THE LOW DEPARTS. 
HIPRES BUILDS IN FROM THE WEST WED NGT AND THU. A COLD FRONT MOVES 
THRU FRI NGT/SAT MRNG. BREEZY NWLY WINDS EXPECTED BEHIND THE FRONT 
ON SAT.

.MARINE...
GENERALLY QUIET CONDITIONS EXPECTED OVER THE WATERS OVER THE NEXT 24 
HOURS. WINDS WILL SHIFT TO THE NORTHWEST BEHIND A TROUGH 
OVERNIGHT...WHICH MAY BE 10 TO 15 KT DOWN THE MAIN CHANNEL OF THE 
BAY TODAY BUT GUIDANCE KEEPS WINDS BELOW SCA THRESHOLDS. WEAK 
BACKDOOR FRONT SLIPS SOUTH OF THE WATERS TONIGHT. 

LGT RA/SN EXPECTED FOR THE WATERS WED AS AN AREA OF LOPRES MOVES 
THRU. HIPRES BUILDS IN WED NGT AS THE LOW MOVES INTO THE WRN 
ATLANTIC. DECENT PRESSURE SURGE HAS THE POTENTIAL TO PRODUCE NW 
GUSTS APPROACHING SCA CRITERIA ACROSS PORTIONS OF THE WATERS LATE 
WED NGT INTO THU MRNG.

LGT WINDS FOR THE END OF THE WEEK WITH HIPRES IN CONTROL. A COLD 
FRONT WILL MOVE THRU FRI NGT INTO SAT MRNG. GUSTY NW WINDS THIS 
WEEKEND IN WAKE OF FROPA.

.CLIMATE...
A CONTINUED LOOK AT THIS WINTERS TEMPS SO FAR 12/1-2/5...

SITE    AVG TEMP RANK

DCA 42.6 5TH WARMEST SINCE 1871

BWI 40.0 12TH WARMEST SINCE 1870 

IAD39.33RD WARMEST SINCE 1971

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

SYNOPSIS...BPP/JRK
NEAR TERM...BPP
SHORT TERM...JRK
LONG TERM...JRK
AVIATION...BPP/JRK
MARINE...BPP/JRK
CLIMATE...ABW