FXUS61 KCTP 151236
AFDCTP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
736 AM EST TUE DEC 15 2009

.SYNOPSIS...
A COLD FRONT WILL TRAVERSE THE AREA THIS MORNING...FOLLOWED BY A
SURGE OF COOLER AIR THROUGH TONIGHT. THIS WILL BE THE START OF AN
EXTENDED PERIOD OF BELOW NORMAL TEMPERATURES...AND MOUNTAIN SNOW
SHOWERS RIGHT INTO THE UPCOMING WEEKEND. AN AREA OF LOW PRESSURE
MAY DEVELOP ALONG THE SOUTHEAST COAST OF THE U.S. SATURDAY NIGHT
AND MOVE NORTHEAST...BRINGING A CHANCE FOR SOME SNOW SUNDAY INTO
MONDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
LATEST OBS SUGGEST COLD FNT IS JUST EAST OF AN IPT/RSP LINE AS OF
1230Z. AS THE FNT TRAVERSES THE LWR SUSQ VLY BY 14Z...XPC LOW
STRATUS AND FOG TO SCOUR OUT FAIRLY QUICKLY AS WNDS PICK UP AND
SHFT TO THE WEST.

DAYTIME HIGHS HAVE BEEN REACHED ACROSS MUCH OF WEST-CENTRAL
PENN EARLY THIS MORNG...AND LOOK FOR FALLING TEMPS THRU THE DAY.
THE REMAINDER OF TDY..ALONG WITH THE OVERNIGHT PD WILL BE
DOMINATED BY A TYPICAL WINTERTIME POST-FNTL REGIME...WITH LAKE
EFFECT SNOW SHOWERS OVER THE ALLEGHENY HIGHLANDS. THE COLDEST AIR
ALOFT WILL SURGE INTO THE AREA LATER TNT FOLLOWING THE PASSAGE OF
MID/UPR LVL TROUGH AXIS AND SECONDARY COLD FNT. HI RES MDLS SHOW A
MULTI-BAND LES CONFIGURATION SETTING UP WITH THE NW MTNS AND
LAURELS LKLY PICKING UP AN INCH OR TWO BY WED AM. AS THE S/WV
TROUGH TAKES ON A NEGATIVE TILT INTO NRN NEW ENG...LOW PRES OVR
DOWNEAST MAINE AND CANADIAN MARITIMES WILL DEEPEN AND TIGHTEN THE
GRADIENT OVR CENTRAL PENN...RESULTING IN GUSTY WNWLY WNDS
20-30KTS.

&&

.SHORT TERM /WEDNESDAY/...
TROUGH AXIS SWINGS THRU MID-ATLANTIC REGION AS FRONTAL BNDRY IS 
POISED TO PASS THRU PA EARLIER IN THE DAY...WITH A STEADY FEED OF 
COOLER AIR FILTERING INTO THE REGION. BNDRY LYR MOISTURE REMAINS 
SHALLOW UNTIL LATE AFTN/EVE...ONCE A WEAK VORT LOBE PIVOTS ARND 
TROUGH AXIS EARLY WED. THIS SHUD ELEVATE INVERSION HEIGHTS FOR THE 
NW MTNS...WITH MOISTURE ARRIVING IN THE DGZ OR ARND THE -20DEG C 
LYR. THUS STILL ANTICIPATE THAT LGT ACCUMS TUE NGT...THEN AGAIN FOR 
WED. ATTM IT APPEARS SUB-ADVISORY CRITERIA...HOWEVER A FEW 
LOCAL/HIGH TERRAIN AREAS COULD REACH CRITERIA. TEMPS WILL FALL INTO 
THE U-TEENS/L20S NW...M20S/U20S ELSEWHERE.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
GUIDANCE SUGGESTS A PERSISTENT PATTERN ARRIVING BEHIND FRONTAL 
PASSAGE TUE FOR WED THRU EARLY NEXT WEEK. CONFIDENCE BEGINNING TO 
INCREASE WITH RESPECT TO BLOCK OVER GREENLAND HOLDING THRU THE 
WEEKEND. EXPECT MID-LVL TROUGH TO ALSO MAINTAIN ITSELF ACROSS 
ONTARIO/QUEBEC...WHICH MAY ALLOW FOR WEAK VORT LOBES TO SLIDE SE 
FROM CENTRAL CANADA ACROSS THE GREAT LAKES REGION AND EVENTUALLY 
INTO THE MID-ATLANTIC. 

THE WILDCARD FOR THE SECOND HALF OF THE WEEKEND WILL BE THE 
INFLUENCE OF THE NORTH ATLANTIC BLOCK...AND POTENTIAL FOR A 
RETROGRADING 500MB VORT MAX INTO ONTARIO. A FEW GUIDANCE MEMBERS
STILL HINT AT THIS SCENARIO...HOWEVER THE OVERALL CONFIDENCE IS
THAT A CONTINUED NW FLOW PATTERN WILL MAINTAIN COOL CONDS. PRECIP
APPEARS MINIMAL AS WELL. EXPECT DOWNSLOPING TO KEEP MINIMAL CLOUD
COVER ACROSS THE SUSQ-VALLEY FOR THE AFTN HRS...WITH CONTINUED
UPSLOPE AND LAKE EFFECT CLOUDS ACROSS THE ALLEGHENIES/NW MTNS. MAX
TEMPS SHUD REMAIN UNIFORM FOR NEXT SEVERAL DAYS... ARND 30S TO
U20S NW/CENTRAL...L30S/M30S FOR REMAINDER OF CWFA OVER THE
WEEKEND/EARLY NEXT WEEK. OVERNIGHT LOWS WILL BE MAINLY IN THE
TEENS/L20S...M20S ACROSS THE LOWER SUSQ-VALLEY FOR THE EXTENDED.

ENSEMBLE FORECASTS OF NAO AND PNA CONTINUE TO INDICATE BLOCKING
(NEGATIVE NAO) FOR AT LEAST THE NEXT WEEK...AND PNA RAPIDLY CHANGING
SIGN TO BECOME POSITIVE ON WEDNESDAY AND REMAIN THAT WAY FOR AT
LEAST THE NEXT WEEK. POSITIVE PNA IN TANDEM WITH NEGATIVE NAO
USUALLY PORTENDS SOME ACTIVE WINTER WEATHER...BUT SO FAR THERE IS
NO STRONG SIGNAL EVIDENT IN THE EXTENDED GUIDANCE AND ENSEMBLES...
AND IT APPEARS A COLD NORTHWEST FLOW OVERALL WILL PREVAIL WITH
A LARGE SFC ANTICYCLONE OVER CENTRAL CANADA DIRECTING LOW LEVEL COLD
AIR SOUTHEASTWARD ACROSS THE GREAT LAKES INTO THE NORTHEAST WHILE
A QUASI-STATIONARY AND SLIGHTLY RETROGRADING SOUTHEAST CANADA
UPPER LOW MAINTAINS THE UPPER LEVEL NORTHWEST FLOW.

&&

.AVIATION /13Z TUESDAY THROUGH SATURDAY/...
CLD FNT NOW EAST OF IPT/RSP LINE...AND WILL SWEEP THRU THE SUSQ
VLY BY 14Z. POST-FNTL WNWLY FLOW REGIME WILL ALLOW FOR IMPROVG
CONDS /SCT-BKN CIGS 3.5-6KFT AGL/ SOUTHEAST OF THE MTNS LATER TDY
GIVEN DOWNSLOPE. BFD/JST WL LKLY REMAIN MVFR OR WORSE AS COLDER
AIR MOVG ACRS THE GRT LKS PICKS UP MSTR AND ASCENDS AND HIER
TERRAIN. HI RES MDLS SUGGEST MULTIPLE BANDS OF LES WILL PERSIST
INTO TNT.

OUTLOOK...
MVFR AND OCNL -SHSN BFD/JST. MAINLY VFR ELSEWHERE.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$
SYNOPSIS...STEINBUGL
NEAR TERM...STEINBUGL
SHORT TERM...BEACHLER
LONG TERM...DEVOIR/BEACHLER
AVIATION...STEINBUGL