FXUS61 KCTP 150911
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
411 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/...
LOW PRES MOVG INTO UPSTATE NY WILL PUSH ENEWD INTO MAINE BY THIS
EVE. LATEST RADAR/STLT IMAGERY AND SFC OBS SUGGEST THE COLD FRONT
IS MOVG ACROSS WEST-CENTRAL PENN...ACCOMPANIED BY SCT LGT RAIN
AND SPRINKLES. LINEAR EXTRAPOLATION SHOWS THE FRONT EXITING THE
ERN CWA BY 15Z. TEMPERATURES HAVE WARMED AHD OF THE FNT INTO THE
MID AND UPPER 40S OVR SW PENN...AND INTO THE MID 50S ACROSS NRN
WV. LOOK FOR STEADY TO FALLING TEMPS IN THE WAKE OF THE
FROPA...WITH DAYTIME HIGHS LKLY OCCURRING PRIOR TO SUNRISE IN THE
WRN ZONES.
NEARLY CALM AIR AND RELATIVELY HIGH BL MSTR HAS RESULTED IN AREAS
OF FOG AND LOW ST ACROSS THE LWR SUSQ VLY. XPC POST-FNTL FLOW AND
DOWNSLOPING WNDS TO SCOUR OUT LLVL MSTR BY LATE MORNING/EARLY
AFTN...THEN TEMPS STEADY TO SLOWLY FALLING AFT 18Z OR SO. WNWLY
WDS SHUD PICK UP THROUGH TONIGHT AS GRADIENT TIGHTENS IN RESPONSE
TO THE AFOREMENTIONED LOW DEEPENING OVR DOWNEAST MAINE/MARITIMES.
THE SECOND HALF OF THE DAY AND 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 WITH THE NW MTNS AND LAURELS LKLY PICKING UP AN
INCH OR TWO BY WED AM.
&&
.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 /09Z TUESDAY THROUGH SATURDAY/...
WEAK SFC LOW OVR LK ONTARIO AT 05Z WL MOVE ENE INTO MAINE BY THIS
EVE. TRAILING COLD FNT AND ASSOC WND SHFT WL CROSS THE REGION FM
W-E BY MID MORNING. CIGS AND VSBYS WILL REMAIN IN THE MVFR AND IFR
CATG THRU MID MORNING. ANY LGT RNFL/SHWRS WL MAINLY BE CONFINED
TO WEST OF AOO/UNV/IPT...WITH SOME PATCHY DZ/BR ACRS THE CENTRAL
AND ERN TERMINALS.
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
