nws st.college--shifting north (watches-warnings)

[2001kx]

000
FXUS61 KCTP 050338 CCA
AFDCTP

AREA FORECAST DISCUSSION...CORRECTED FOR WINT STM WARNING AREA
NATIONAL WEATHER SERVICE STATE COLLEGE PA
945 PM EST THU DEC 4 2003

.UPDATE...

WHAT AN INTERESTING...AND APPROPRIATE WAY WEATHERWISE TO START THE
FIRST WEEKEND OF THE FIRST WINTER MONTH.

SEVERAL AREAS OF WEAK LOW PRESSURE (ONE ALONG THE GULF COAST OF THE
FLORIDA PANHANDLE...THE SECOND ACROSS SOUTHERN ILLINOIS...THE THIRD
ACROSS NRN MINNESOTA WILL GRADUALLY CONSOLIDATE INTO
ONE...INTENSIFYING AREA OF LOW PRESSURE NEAR THE DELMARVA COAST BY
MIDDAY SATURDAY.

MODELS HAVE NOW (AND FOR GOOD REASON THAT I'LL EXPLAIN BELOW)
TRENDED MORE NORTHWEST WITH THEIR PRIMARY FORCING AND RESULTANT
STORM TOTAL QPF/SNOWFALL. EXTENSIVE...COLD CONVEYOR BELT PRECIP (WET
SNOW AND RAIN) EXTENDED FROM THE VIRGINIA COAST...ALL THE WAY WEST
TO SOUTHERN WISCONSIN. ANOTHER AREA OF VARYING INTENSITY SNOW WAS
MOVING SOUTHEAST FROM THE UPPER PLAINS IN ASSOCIATION WITH A VERY
POTENT UPR THROUGH/130 KT 300 HPA JET STREAK.

SNOWFALL ACROSS CENTRAL PENN WILL BE SLOW TO SPREAD NORTH DURING THE
DAY FRIDAY...AS AN INITIAL JET MAX MOVES FROM THE TENNESSEE VALLEY
THIS EVENING TO OFF THE VIRGINIA COAST. UVVEL BENEATH THE LEFT EXIT
REGION OF THIS JET WILL CARRY LIGHT...TO MDT SNOW INTO OUR SRN ZONES
LATE TONIGHT...THEN CONTINUING ACROSS THE EXTREME SE PARTS OF THE
CWA (YORK...LANCASTER...LEBANON CTYS) FOR PART OF TOMORROW).

IT APPEARS THAT THERE SHOULD BE A RELATIVE MIN IN PRECIP DURING THE
AFTERNOON/EARLY EVENING HOURS FRIDAY...THOUGH THE 18Z GFS SUGGESTS
THAT THE FRONTOGENETIC FORCING (850 & 700 HPA) WITH THIS INITIAL
WAVE WILL INCREASE AS IT COMBINES WITH A STRENGTHENING JET ENTRANCE
REGION FROM THE SRN NEW ENGLAND COAST...WEST INTO THE MID SUSQ
VALLEY. SHOULD THIS OCCUR...WE COULD SEE LIGHT SNOW SPREAD NW OF
STATE COLLEGE AND WILLIAMSPORT DURING THE AFTERNOON AND GIVE AN INCH
OR TWO BY DARK...AND UPWARDS TO 5 INCHES NEAR YORK...HARRISBURG AND
LANCASTER. WILL BE WAITING TO SEE THE 00Z GUIDANCE BEFORE MAKING A
SIGNIFICANT CHANGE TO TOMORROW'S SNOW.

BIGGEST CHANGE IN THE UPPER AIR PATTERN ACROSS THE ERN CONUS...WHICH
CASCADES RIGHT DOWN TO THE TRACK OF THIS EVOLVING STORM...IS OVER
SERN CANADA. ALL MODEL RUNS WEDNESDAY...TRENDED SOUTH WITH THE STORM
TRACK BASED ON THE PRESENCE OF A STRONGER SERN CANADA SHORT WAVE
DIGGING SE AND CREATING A STRONGER CONFLUENT ZONE ALOFT/ SFC HIGH
PRESSURE FURTHER SOUTH ACROSS NEW YORK AND NEW ENGLAND. CURRENT
LOCATION OF THIS FEATURE IS OVER EXTREME SERN QUEBEC PROVINCE...AND
HEADING EAST. THIS KEY FEATURE WILL ALLOW THE UPR MIDWEST SHORT WAVE
TO AMPLIFY MORE AND SLOW AS IT REACHES THE EAST COAST AND COMBINES
WITH THE FORCING ALREADY IN PLACE VIA THE ABOVE NOTED JET ENTRANCE
REGION FROM PENN TO SRN NEW ENGLAND.

ETA IS SOMEWHAT FURTHER SOUTH WITH THE QPF/SNOW AXIS (THOUGH A
FEW..2 OUT OF 10...ENSEMBLE MEMBERS SHOW OVER AN INCH OF QPF ALMOST
OVER THE NW MTNS OF PENN)...AND FASTER WITH THE EXIT OF THE STORM
OFF THE MID ATLANTIC COAST. THIS APPEARS BASED ON THE IMPACT OF A
STRONGER/FURTHER SOUTH NRN STREAK SHORTWAVE DROPPING SE ACROSS
CENTRAL ONTARIO. STILL...THIS MODEL PAINTS A 5 TO 8 INCH SWATH OF
SNOW ALONG AND SE OF A LINE FROM KAOO...TO KUNV AND KSEG.

THIS "SHOULD" ALL TRANSLATE INTO A MAJOR SNOWSTORM FOR MUCH OF
CENTRAL AND SOUTHERN PENNSYLVANIA WITH THE POTENTIAL FOR OVER A FOOT
OF SNOW WHERE MESOSCALE/CSI SNOW BANDS ARE MORE PERSISTENT (TARGET
AREA IN OUR COUNTY FCST & WARNING AREA WOULD BE FROM SCENT PENN TO
THE EAST CENTRAL MTNS).

CONSIDERING ALL OF THIS...THE STEADIEST AND HEAVIEST SNOW WILL FALL
FROM THE SECOND HALF OF FRIDAY NIGHT...INTO THE AFTERNOON HOURS
SATURDAY. WITH TEMPS IN THE LOW TO MID 30S CENTRAL AND SOUTH AND
LVLL WET BULB TEMPS BELOW ZERO...SLEET OR FREEZING RAIN SHOULD NOT
MIX IN SOUTHEAST OF INTERSTATE 81...EXCEPT FOR PERHAPS SOME FREEZING
DRIZZLE OR POSSIBLE FRIDAY.

*** 00Z ETA JUST IN THROUGH 36 HOURS...AND IS ALMOST IDENTICAL WITH
THE TRACK OF THE 18Z GFS WITH THE UPPER LOW CENTER AT THE NRN TIP OF
THE CHES BAY SAT MORNING (WHICH IS STILL ABOUT 6 HRS FASTER THAN THE
GFS).***

COORDINATED WITH SURROUNDING OFFICES. WE ARE CURRENTLY EXPANDING
WATCHES FURTHER NORTH AND WEST (TO THE NCENT MTNS) FOR LATER IN THE
DAY FRIDAY -> SATURDAY.

WILL HOIST WINT STORM WARNINGS FOR FRIDAY INTO SATURDAY ACROSS THE
PREVIOUS ADVISORY AREAS OF THE SOUTH (AND EXPAND IT A FEW LAYERS OF
COUNTIES TO THE NORTH) BASED ON 00Z ETA CONSENUS WITH 18Z
GFS...RECENT RADAR TRENDS...AND TO BLEND WITH PBZ'S WARNINGS.