FXUS61 KCTP 151821
AFDCTP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
121 PM EST TUE DEC 15 2009

.SYNOPSIS...

COLDER AIR WILL CONTINUE TO FILTER INTO THE REGION BEHIND A COLD
FRONT MOVING OFF THE EASTERN SEABOARD. THIS IS THE START OF
AN EXTENDED PERIOD OF BELOW NORMAL TEMPERATURES...AND MOUNTAIN
SNOW SHOWERS THAT WILL LAST 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 WEDNESDAY/...

TEMPS ARE BEGINNING TO FALL OVER NW PA AS WINDS TURN WESTERLY.
FORECAST IS PRETTY MUCH ON TRACK WITH THE BEST CHANCE OF PRECIP
CONFINING ITSELF TO MY WESTERN AND NORTHERN HIGH TERRAIN ZONES. 

THE REMAINDER OF THE DAY..ALONG WITH THE OVERNIGHT WILL BE
DOMINATED BY A MORE OR LESS TYPICAL WINTERTIME POST-FRONTAL
REGIME...WITH LAKE EFFECT SNOW SHOWERS DOWNWIND OF LAKE ERIE AND
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 DOWN-EAST MAINE AND
CANADIAN MARITIMES WILL DEEPEN AND TIGHTEN THE GRADIENT OVR
CENTRAL PENN...RESULTING IN GUSTY WNWLY WNDS 20-30KTS.

MODEL SOUNDINGS INDICATE THE INVERSION LOWERS SIGNIFICANTLY DURG
THE DAY WED SO THE BEST WINDOW OF OPPORTUNITY FOR ACCUM SNOW WILL
LIKELY BE CLOSING DURING THE MORNING. IT WILL PROBABLY REMAIN
CLOUDY HOWEVER...WITH A GUSTY WNW WIND AND SCATTERED SNOW SHOWERS
CONTINUING. 

&&

.SHORT TERM /WEDNESDAY NIGHT/...

HIGH CONTINUES TO BUILD IN WED NIGHT. TRAJECTORIES CONTINUE TO
INDICATE STUBBORN CLOUDS AND SCATTERED SNOWS OVER NWRN PA.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
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 WILD CARD 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 /18Z TUESDAY THROUGH SUNDAY/...

AS COLDER AIR POURS INTO THE STATE...POST-FRONTAL WNWLY FLOW
REGIME WILL ALLOW FOR IMPROVG CONDS OVER MOST OF CENTRAL AND ERN
PA...WHILE THE WESTERN HIGH TERRAIN TERMINALS LIKE JST/BFD REMAIN
MVFR OR WORSE AS COLD AIR MOVG ACROSS THE GRT LAKES PICKS UP
MOISTURE AND DEPOSITS SCATTERED SNOW SHOWERS OVER THE USUAL LAKE
EFFECT AND UPSLOPE AREAS. HI RES MDLS SUGGEST MULTIPLE BANDS OF
LES WILL PERSIST INTO TNT. ONE MODEL EVEN SAGS A SNOW BAND INTO
STATE COLLEGE AROUND 03Z. IF IT WERE TO VERIFY...IFR AND SNOW
WOULD MOVE IN FOR AN HOUR OR TWO...BUT THE MODELS ARE NOTORIOUSLY
BAD AT FORECASTING SUCH MESOSCALE ROGUE ELEMENTS. AT THIS STAGE
THE PRUDENT THING IS TO LOOK TO CLIMO WHICH INDICATES UNDER THIS
FLOW REGIME AT THIS TIME OF YEAR...JST/BFD NORMALLY ENJOY THE
WORST CONDITIONS.

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

&&

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

&&

$$
SYNOPSIS...LA CORTE
NEAR TERM...LA CORTE
SHORT TERM...BEACHLER
LONG TERM...DEVOIR/BEACHLER
AVIATION...LA CORTE