000
FXUS61 KCTP 032353
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
653 PM EST WED DEC 3 2008
.SYNOPSIS...
A COLD FRONT WILL CROSS THE COMMONWEALTH ON THURSDAY...ACCOMPANIED
BY A SEVERAL HOUR PERIOD OF RAIN SHOWERS ACROSS THE SUSQUEHANNA RIVER
VALLEY...AND RAIN SHOWERS MIXING WITH...THEN CHANGING TO SNOW
SHOWERS ACROSS THE NORTHERN AND WESTERN MOUNTAINS OF PENNSYLVANIA.
LAKE EFFECT SNOW SHOWERS WILL PREVAIL ACROSS PARTS OF WESTERN AND
NORTHERN PENNSYLVANIA ON FRIDAY INTO SATURDAY AHEAD OF AN ALBERTA
CLIPPER WHICH WILL SPREAD ANOTHER ROUND LIGHT SNOW OR SNOW SHOWERS
ACROSS THE AREA LATER SATURDAY INTO SUNDAY. BELOW NORMAL
TEMPERATURES WILL PERSIST THROUGH THE MIDDLE OF NEXT WEEK WITH A
CHANCE FOR MORE SIGNIFICANT RAIN AND SNOW DEVELOPING LATE TUESDAY
INTO WEDNESDAY.
&&
.NEAR TERM /UNTIL MIDNIGHT TONIGHT/...
CLEAR TO PARTLY CLOUDY SKIES WILL BE FOLLOWED BY A QUICK INCREASE
IN CLOUDS FROM THE SOUTHWEST EARLY THIS EVENING AS THE EASTERN
EDGE OF A 925 TO 850 HPA...35 TO 45 KT JET MOVES NORTHEAST FROM THE
OHIO VALLEY. THE LEADING EDGE OF THIS THICKENING...ALTO/STRATO CU
LAYER WILL REACH THE WRN PENN MTNS BETWEEN 22-23Z...THE CENTRAL
RIDGE AND VALLEY REGION BETWEEN 23Z AND 01Z...AND THE MID/LWR SUSQ
VALLEY BETWEEN 02Z AND 05Z. RAIN AND SNOW SHOWERS WILL DEVELOP
ACROSS THE NW MTNS AROUND OR SHORTLY BEFORE MIDNIGHT PER 12Z NAM
AND 09Z SREF PLUME DIAGRAMS.
SOUTH/SOUTHWEST WINDS WILL INCREASE TO 10-15 MPH WITH GUSTS
(MAINLY ON THE RIDGES AOA 1500 FT MSL) OF AROUND 25 KTS.
AN INITIAL...SEVERAL DEG TEMP DROP (EARLY THIS EVENING JUST PRIOR TO
THE CLOUD INCREASE) WILL LEVEL OFF FOR MUCH OF THE OVERNIGHT HOURS
AS LLVL WARM ADVECTION AND THE CLOUDS HELP TO COMPENSATE FOR ANY
EVAPORATIONAL COOLING AS THE PRECIP FALLS INTO THE INITIALLY DRY AIR
WITH DEWPOINTS IN THE TEENS/20S.
&&
.SHORT TERM /MIDNIGHT TONIGHT THROUGH THURSDAY NIGHT/...
HAVE INCREASED POPS FOR THURSDAY IN ALL LOCATIONS AS THERE IS A
STRONG AGREEMENT BETWEEN OPERATIONAL MODELS AND SHORT RANGE ENSEMBLE
MEMBERS OF LIGHT ONE TO TWO TENTHS OF QPF (MIXED RAIN/WET SNOW
SHOWERS - ACROSS THE CENTRAL AND NW MTNS) LATE TONIGHT THROUGH
THURSDAY AFTERNOON.
LITTLE OR NO SNOW ACCUMULATION IS EXPECTED THROUGH 12Z FRIDAY
ACROSS THE CENTRAL VALLEYS AND SUSQ REGION....WITH A GENERAL
COATING TO 2 INCHES ACROSS THE LAURELS NORTH TO ELK AND POTTER
COUNTIES AND UP TO 3 OR 4 INCHES ACROSS A FEW LOCATIONS IN THE
SNOWBELT OF NW WARREN COUNTY.
NOT TOO IMPRESSED WITH THE POTENTIAL FOR SIGNIFICANT LES ACROSS OUR
NW ZONES AS THE DEPTH OF THE COLD AIR/SUBSIDENCE INVERSION HEIGHT
WILL BE LOWERING IN LATE THE AFTERNOON TO AT/OR BELOW 4 KFT AGL WITH
THE MEAN SFC-850 HPA WIND VEERING AROUND TO ABOUT 305-310 DEG. THE
COMBINATION OF COLD ADVECTION ALOFT AND LLVL CYCLONIC FLOW WILL
BRING THE BEST CHC FOR WIDESPREAD SNOW SHOWERS OR A PERIOD OF STEADY
SNOW TO THE WRN MTNS DURING THE MORNING THROUGH EARLY AFTERNOON
HOURS.
TEMPS WILL BUDGE LITTLE ACROSS THE WRN MTNS DURING THE DAY...WITH
THE MIDDAY PEAK ACROSS THE SUSQ VALLEY...FOLLOWED BY A RATHER
SHARP DROP IN THE MID/LATE AFTERNOON. TEMPS WILL BE WITHIN A FEW
DEG OF 30F ACROSS THE NW MTNS BEFORE FALLING INTO THE MID 20S BY
LATE AFTERNOON. HIGHS RANGING FROM THE MID 30S TO MID 40S
RESPECTIVELY ACROSS CENTRAL AND SE ZONES AROUND 17Z-18Z...WILL ALSO
FALL AT LEAST SEVERAL DEG F BY 21Z.
SCATTERED MAINLY MTN SNOW SHOWERS WITH LIGHT ADDITIONAL
ACCUMULATION WILL PERSIST THURSDAY NIGHT WITH JUST FLURRIES OR AN
ISOLATED SNOW SHOWER OVER THE CENTRAL VALLEYS. LOWS EARLY FRIDAY
WILL RANGE FROM THE MID/UPR TEENS OVER THE WRN AND NRN MTNS...TO
BETWEEN 20 AND 25F ELSEWHERE.
&&
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
BROAD UPPER TROF WILL REMAIN ALIGNED ACROSS THE GREAT LAKES FRIDAY.
THE CYCLONIC FLOW AND COLD TEMP PROFILES WILL BE SUPPORTIVE OF BANDS
OF LAKE EFFECT/UPSLOPE SNOW...AS 850MB TEMPS FALL TO -1 TO -2SD BLW
NORMAL /AROUND -15C/. NWLY FLOW WILL BACK TO MORE WLY...SHIFTING
AXIS OF HEAVY SNOWS MORE EAST OF THE LAKES WHERE LONG FETCH
TRAJECTORIES MAY SET UP. MODELS SUGGEST AN E-W ORIENTED BAND ALONG
THE PA/NY BORDER. LGT SNOW ACCUMS SHOULD BE CONFINED TO THE
NORTHWEST MOUNTAINS...WITH UP TO THREE INCHES POSSIBLE OVER THE
SNOWBELT REGION OF NW WARREN CO.
SNOW SHOWERS SHOULD BECOME DISORGANIZED AND GRADUALLY DIMINISH EARLY
FRIDAY NIGHT AS THE LOW LEVEL FLOW BACKS MORE TO THE WSW AND HIGH
PRES /BRIEFLY/ BUILDS IN FROM THE OH VLY. HIGH TEMPS WILL GENERALLY
RANGE BTWN 10 TO 15 DEGS BLW NORMAL ON FRI.
AN ALBERTA CLIPPER LOW WILL SWEEP SOUTHEAST THROUGH THE GREAT LAKES
ON SATURDAY...AND ROTATE INTO THROUGH THE LOWER LKS AND INTO THE ST
LAWRENCE VLY BY SUNDAY. MEANWHILE...AS THE ASSOC UPPER TROF BEGINS
TO TAKE ON A SLIGHT NEGATIVE TILT...MODELS AND ENSEMBLES INDICATE
SECONDARY CYCLOGENESIS OFF THE MID ATLC COAST. THE GEFS SHOWS
INCREASING SPREAD IN THE MSLP FIELD AS THE SECONDARY LOW DEEPENS AND
LIFTS NWD INTO NEW ENGLAND. THE PROGRESSIVE NATURE OF THE UPSTREAM
MID/HIGH LVL FLOW FAVORS A COASTAL SYSTEM MORE OFFSHORE /WHICH IS
GENERALLY SUPPORTED AMONGST MOST OPERATIONAL GUID/...SUGGESTING
LITTLE DIRECT IMPACT ON CENTRAL PENN. THE ERN/NERN ZONES MAY BE
VULNERABLE TO SOME WRAP-AROUND DEFORMATION TYPE SNOWS DEPENDING UPON
HOW CLOSE THE LOW TRACKS TO THE COAST. HOWEVER...DETAILS ARE
UNCERTAIN AND WILL NEED TO BE RESOLVED IN THE COMING DAYS. BUT
ATTM...IT APPEARS THE MAIN IMPACT WILL BE WITH THE CLIPPER...WHICH
SHOULD BRING A PD OF MAINLY LGT WAA-TYPE SNOW TO THE AREA LATE SAT
INTO SUN.
VERY COLD AIR WILL BE DIRECTED INTO THE REGION AS THE UPPER TROF
AXIS SHIFTS EAST OF THE GREAT LAKES SUN NGT INTO MON. THE BLUSTERY
CYCLONIC/NWLY FLOW SHOULD LEAD TO MORE INTENSE LAKE EFFECT AND
OROGRAPHIC SNOW SHOWERS SUNDAY NIGHT INTO EARLY MONDAY...WITH SOME
MOD ACCUMS PSBL OVER THE SNOWBELT AND UPSLOPE REGIONS. GEFS DATA
SHOWS HIGH PRESSURE MOVG INTO THE AREA FOR MONDAY...THEN
RETREATING OFF THE EAST COAST MON NGT.
THE OPERATIONAL GFS/ECMWF ALONG WITH THE GEFS AND NAEFS CONTINUE TO
SUGGEST THE POTENTIAL FOR A SIGNIFICANT PRECIPITATION EVENT EAST OF
THE MISSISSIPPI IN THE TUE-THUR /DEC 9-11/ TIMEFRAME. TEMPERATURES
WILL TO MODERATE FROM THE PLAINS STATES EWD IN RESPONSE TO HEIGHT
FALLS OVER THE ROCKIES...WITH MOST MDL AND ENSEMBLE GUID IN
AGREEMENT IN DEPICTING A TROF DEVELOPING INVOF THE CENTRAL U.S.
HOWEVER...THE DEPTH/LOCATION OF THE TROF ARE UNCLEAR EVIDENCED BY
THE LARGE SPREAD...WHICH WILL PLAY A CRUCIAL ROLE IN THE TRACK OF
A DEVELOPING SURFACE WAVE DOWNSTREAM. THE SYNOPTIC SET-UP FAVORS
A DECENT RETURN FLOW OF GOMEX MSTR INTO THE SE...WHICH COULD BE
EASILY TRANSPORTED NWD INTO THE SRN APPALACHIANS/MID ATLC REGION BY
THE MIDDLE OF NEXT WEEK. STAY TUNED.
&&
.AVIATION /00Z THURSDAY THROUGH MONDAY/...
LATEST IR SHOWING HIGH BASED CLOUDS SLOWLY DRIFTING TOWARDS
PENNSYLVANIA AIRFIELDS. CIGS AOA 20KFT AGL WILL GRADUALLY LOWER AS
FRONTAL BNDRY APPROACHES FROM THE WEST. EXPECT VFR CIGS TO HOLD
THRU 04Z WHEN LOW/MID LVL MOISTURE ARRIVES. DEEP LAYERED RH
SATURATES ARND 07Z FOR KBFD/KAOO/KJST/KUNV...THUS EXPECT ORGANIZED
PRECIP TO GET GOING REDUCING CIGS TO MVFR/IFR. CAN/T RULE OUT A
TEMPO CIGS/VSBYS ARND IFR/LIFR BTWN 10-15Z FOR A FEW AIRFIELDS.
MIXED LYR IS GREATEST CONCERN AFT 11Z...AS STRONG WIND GRADIENT
ARRIVES JUST OFF THE DECK AT 1500-2000KFT AGL AT 40-45KTS. WIND SHEER
APPEARS TO BE UNI-DIRECTIONAL...HOWEVER SPEED SHEER IS EVIDENT
FROM THE WEST. EXPECT GUSTY SFC WINDS ARND 20-25KTS...HOWEVER IF
MIXED LYR PROGGED BY LCL HI-RES WRF/S OF 1500FT IS MIXED DOWN TO
SFC...GUSTS TO 30-35KTS WILL BECOME VERY POSSIBLE DURING DIURNAL
CYCLE THUR.
AS COLDER AIR POURS INTO CENTRAL PA...RA WILL BECOME MIXED WITH SN
THEN CHANGE TO ALL SN. LES WILL REMAIN POSSIBLE...HOWEVER GIVEN
SUCH A STRONG WIND GRADIENT RESONANCE TIME OVER LAKE/S HURON/ERIE
WILL BE CUT DOWN...HAMPERING ORGANIZED LES BANDS FOR KBFD AND
ALLOWING CELLULAR OR SCT SHSN. AFT 21Z WINDS WILL STEADILY
DIMINISH...ALLOWING BETTER LES BANDS TO FORM AND PROVIDE
PERIODIC IFR/LIFR CIGS/VSBYS TO KBFD AND POSSIBLY KAOO/KUNV.
PERSISTENT WEST TO NW FLOW WILL MAINTAIN WIDESPREAD MVFR CIGS AND
OCNL IFR CIGS AND MVFR VSBYS IN SCATTERED SNOW SHOWERS THROUGH THE
DAY FRIDAY THEN AGAIN SAT AFTERNOON/NIGHT. BEYOND SUN THINGS LOOK
TO REMAIN COLD WITH PERIODS OF LES AND SNOW SHOWERS FOR CENTRAL PA
AIRFIELDS.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...LAMBERT
NEAR TERM...LAMBERT
SHORT TERM...STEINBUGL
LONG TERM...STEINBUGL
AVIATION...LAMBERT/BEACHLER
