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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KCTP 091807
AFDCTP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
107 PM EST TUE FEB 9 2010

.SYNOPSIS...
A LOW PRESSURE SYSTEM DEVELOPING OVER THE OHIO VALLEY TO THE
CENTRAL GULF COAST WILL MOVE NORTHEASTWARD TONIGHT...THEN
REDEVELOP AND RAPIDLY INTENSIFY JUST OFF THE MIDDLE ATLANTIC COAST
BY WEDNESDAY MORNING. THIS SYSTEM WILL PRODUCE MODERATE TO HEAVY
SNOW OVER MUCH OF CENTRAL PENNSYLVANIA BEFORE TAPERING OFF
WEDNESDAY NIGHT. COLD AND BRISK CONDITIONS WITH MOUNTAIN SNOW
SHOWERS CAN BE EXPECTED IN THE WAKE OF THIS SYSTEM...WHICH WILL
LIKELY PERSIST INTO THE UPCOMING WEEKEND.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
IR IMAGERY SHOWS THICK CLOUD COVER OVER WRN HALF OF PA...THOUGH
THE SUN IS VISIBLE THROUGH THOSE CLOUDS HERE A THE OFFICE. SFC OBS
INDICATE SNOW HAS MOVED INTO SWRN CENTRAL PA...BEGINNING AT JST
AND AOO.

CLOUDS WILL LOWER AND THICKEN THROUGH THE AFTN AS 500MB VORT MAX
PUSHES INTO THE OH RVR VALLEY TDY AND 850MB LOW LIFTS NE INTO
CENTRAL OH AND STRENGTHENS. SN WILL STEADILY OVERSPREAD PA FROM W
TO E. WRF- ARW INDICATES GOOD OMEGA...LIFT...IN THE SATURATED
DENDRITIC GROWTH ZONE AFT 18Z ACROSS THE WESTERN PORTIONS OF THE
CWFA. AT ONSET SN RATIOS COULD BE ARND 14:1 OR 16:1 THEN DECREASE
AS ADDTL MOISTURE ADVECTS INTO THE BNDRY LYR WITH RATIOS ARND 12:1
OR 14:1 FOR THE EVENT OR A FUNCTION OF RIMING. DEEP LAYERED
MOISTURE HOLDS ACROSS THE REGION THRU 09Z WED...THEN RELATIVELY
DRIER AIR STARTS TO ENTRAIN ABOVE THE DGZ ACROSS THE WESTERN THIRD
OF THE CWFA SUGGESTING SNOW RATES MAY BACK OFF.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/...
WINDS WILL BECOME SE TO E AS 850MB U-WIND ANOMS OF 20KTS ARE PROGGED
ARND -1 TO -2 STD DEV AT ONSET. AS COASTAL LOW RAPIDLY INTENSIFIES
EARLY WED THOSE ANOMS DEEPEN OFF THE NJ COAST. THIS POSES MORE OF AN
IMPACT TO LOCATIONS ALONG AND SOUTHEAST OF I-81 OVERNIGHT THRU WED
AS WINDS WILL BECOME BREEZY WED MORNING.

GEFS/SREF PLUMES ARE CLUSTERED ARND 0.6 TO 0.8 INCHES QPF THRU 12Z
WED FOR CENTRAL/SOUTHWEST PORTIONS OF THE CWFA. FOR THE LOWER SE
PORTIONS OF THE CWFA THIS INCREASES TO ARND 0.8 TO 1.1
INCHES...WHICH IS SLIGHTLY HIGHER. BASED ON AFOREMENTIONED SN RATIOS
THIS SHUD YIELD SNOWFALL TOTALS THRU 12Z WED ARND 2 TO 5 INCHES
ACROSS THE NORTH...6 TO 8 INCHES CENTRAL/SOUTHWEST...AND 8 TO 10
INCHES ACROSS THE SOUTHEAST SECTIONS OF THE CWFA.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
A POTENT MID LVL LOW AND ASSOC S/W TROUGH WILL BE PROGRESSING EWD
ACROSS CENTRAL WV/VA EARLY WED...WITH RAPID INTENSIFICATION AND
CYCLOGENESIS FCST JUST OFF THE MIDDLE ATLANTIC COAST BENEATH 30DM
HEIGHT FALL CENTER. THE PARENT LOW INITIALLY OVER THE UPPER OH VLY
WILL TRANSFER MOST IF NOT ALL OF ITS ENERGY TO THIS SECONDARY
COASTAL LOW/DEVELOPING NOREASTER WHICH IS GENERALLY MORE TYPICAL
OF CLIMATOLOGY. INCREASING ATLC/ELY INFLOW /WHICH IS FCST TO
STRENGTHEN TO +4SD ABOVE NORMAL/ COMBINED WITH STRONG DYNAMICS
ASSOC WITH THE APPROACHING MID/UPPER LOW WILL SUPPORT MOD TO HVY
SNOW ACROSS THE REGION WED MORNING INTO THE AFTN. AS THE 850MB
CIRCULATION TIGHTENS UP OVER CHESAPEAKE BAY AND THE DELMARVA...IT
WILL BE ACCOMPANIED BY AN INTENSE CONVERGENCE/DIVERGENCE COUPLET
SFC AND ALOFT WITHIN THE EXIT REGION OF A 170KT JET MAX ROUNDING
THE BASE OF THE CLOSED MID LVL LOW CENTER TAKING ON A SLGT NEG
TILT AS IT MOVES OFFSHORE. DEEP LYRD WAA AND FGEN FORCING WILL
FAVOR STRONG UVM IN A 5-6 KM LAPSE RATE ENVIRONMENT...WITH THE
HIER RES NAM AND WRF MDLS SUGGESTING SNOWFALL RATES UP TO 2" AN
HOUR OVR PARTS OF THE MID AND LWR SUSQ VLY BTWN 12-18Z IN ONE OR
MORE PIVOTING NE-SW ORIENTED MESOSCALE BANDING STRUCTURES.

SREF/GEFS ENSEMBLE PLUMES ARE IN LINE WITH GRIDDED STORM TOTAL
SNOWFALL AMOUNTS...WITH AN INCREASING TREND NOTED IN THE LAST FEW
RUNS. IN GENERAL...A BLEND OF MDL QPFS YIELDS 24HR /18ZTUE-18ZWED/
LIQUID EQUIVALENTS OF OVER AN INCH IN THE FAR SE TO ROUGHLY 0.50"
ACROSS THE NW MTNS. FINAL SNOWFALL AMOUNTS WERE COMPRISED OF AN
AVERAGE OF 10-14:1 SLR/S RESULTING IN MAX AMOUNTS OVER A FOOT
/12-18"/ ALONG AND SE OF INTERSTATE 81. HOWEVER...MAXIMIZED
LIFT/OMEGAS VIA BUFKIT APPEAR TO BE LOCATED JUST BELOW THE FAVORED
DGZ. THIS SUGGESTS SOME AGGREGATION WHICH MAY LEAD TO A WETTER
SNOW AND COULD CUT DOWN SLIGHTLY ON ACCUMS. AS THE LOW CONTINUES
TO DEEPEN AS IT MOVES AWAY FROM LI...XPC NORTH TO NORTHWEST GRAD
WINDS TO INC TO 15-25MPH WITH HIGHER GUSTS...LKLY LEADING TO
BLOWING AND DRIFTING OF THE SNOW.

A FAIRLY PERSISTENT...COLD NWLY CYC FLOW WILL LKLY PERSIST FOR THE
NEXT SEVERAL DAYS AS THE LOW ACTUALLY RETROGRADES WWD ACRS THE
MARITIMES BACK INTO QUE BY SUN. THE ESTABLISHED MEAN TROUGH IN THE
EAST WILL KEEP COLD AIR/BELOW NORMAL TEMPS LOCKED IN FOR THE
FORESEEABLE FUTURE...WITH PERHAPS SOME ARCTIC AIR SPILLING SEWD FM
NCENT CANADA DIRECTED INTO THE NORTHEAST. THE COLD/UPSLOPE FLOW
ALONG WITH EMBEDDED SW/S SHOULD MAKE FOR PERIODS OF SNOW SHOWERS
ACRS THE ALLEGHENY HIGHLANDS AT LEAST THRU THE REMAINDER OF THE
WORK WEEK.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
-- Changed Discussion --
CONSID HIGH LVL CLOUDS HAVE PUSHED EAST INTO CENTRAL PA...WITH
SLOWLY DETERIORATING CONDS INDICATED BY UPSTREAM AIRFIELDS.
FIRST BAND OF SNOW MOVING THROUGH SWRN CENTRAL PA ATTM WITH LIGHT
SNOW REPORTED AT KJST AND KAOO FOR THE LAST HOUR OR TWO. RADAR
IMAGERY HOWEVER SHOWS A BREAK IN THE PCPN AS THIS BAND LIFTS N OF
THE REGION. EXPECT SNOW TO RETURN AFT 20Z AS AREA OF SNOW
NOW OVER WRN PA MOVES EAST...THEN STEADILY INTO CENTRAL AIRFIELDS
THROUGH THE AFTN.

VSBYS FROM SN/+SN WILL FLUCTUATE BTWN 1SM TO 1/4SM AT TIMES
PRODUCING IFR TO VLIFR CONDS BTWN 03Z- 09Z WED. SLT IMPROV ACROSS
NW MTNS AIRFIELDS AFT 12Z WED.

OUTLOOK...
WED...MAINLY IFR...WITH PERIODS OF LIFR IN SN.
THUR- SAT...MVFR TO VFR CENTRAL/EAST. MVFR AND SCT -SHSN WEST.
-- End Changed Discussion --

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING UNTIL 7 PM EST WEDNESDAY FOR PAZ011-012-
018-019-026>028-035-036-041-042-045-046-049>053-056>059-
063>066.
WINTER STORM WARNING UNTIL 7 PM EST WEDNESDAY FOR PAZ010-017-
024-025-033-034.
WINTER WEATHER ADVISORY FROM 4 PM THIS AFTERNOON TO 7 PM EST
WEDNESDAY FOR PAZ004>006-037.

&&

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