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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KCTP 092104
AFDCTP

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

.SYNOPSIS...
-- Changed Discussion --
A LOW PRESSURE SYSTEM WILL SLIDE TOWARD THE REGION TONIGHT AND
RAPIDLY REDEVELOP AND 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.
-- End Changed Discussion --

&&

.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 PM WEDNESDAY/...
-- Changed Discussion --
POTENT STORM SYSTEM BEGINNING TO AFFECT PENNSYLVANIA LATE THIS
AFTERNOON AS STRONG UPPER ENERGY SLIDES IN FROM THE WEST. THIS
ENERGY WILL BEGIN TO SHIFT TO THE COAST AND RAPIDLY DEEPEN A
COASTAL LOW TONIGHT WHICH WILL BRING A HIGH IMPACT SNOW EVENT TO
EASTERN PA...MAINLY TO LOCATIONS ALONG AND SE OF I-81...AND
SLIGHTLY LESSER AMOUNTS TO CENTRAL AND WEST. THE POTENTIAL
BULLSEYE OF HIGHEST AMOUNTS FROM NEAR HARRISBURG EAST TO NEAR
PHILLY AND ALLENTOWN.

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.
-- End Changed Discussion --

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
-- Changed Discussion --
POTENT WINTER STORM WILL BE HEADED AWAY FROM PA BY WED
NIGHT...LEAVING A MESS BEHIND. BIGGEST STORY FOR WED NIGHT INTO
THU WILL BE STIFF AND GUSTY NORTHWEST WINDS CREATING BLOWING SNOW
AND CHILLY CONDITIONS. TEMPS WON/T SEE A BIG DROP OFF BEHIND THE
STORM...BUT WINDS WILL BRING WIND CHILLS INTO THE SINGLE DIGITS
WED NIGHT INTO THU. MUCH OF THE REGION WILL BEGIN A PERIOD OF
PRECIPITATION-FREE WEATHER WITH PERSISTENT NORTHWEST FLOW...BUT
THE HIGHER ELEVATIONS OF THE WEST AND NORTH WILL SEE MAINLY LIGHT
SNOW SHOWERS DUE TO UPSLOPE FLOW. AN OCCASIONAL SNOW SHOWER COULD
SLIP INTO THE CENTRAL MOUNTAINS DURING THIS TIME...BUT MUCH OF THE
TIME WILL BE DRY.

TEMPS WILL SEE LITTLE CHANGE AS WE PROGRESS THROUGH THE
WEEK...WITH TEMPS GENERALLY AVERAGING A COUPLE OF DEGREES BELOW
NORMAL. POTENTIAL FOR SOME LIGHT SNOW EARLY NEXT WEEK...SO EDGED
POPS UP ABOVE NORMAL FOR THAT TIME FRAME.
-- End Changed Discussion --

&&

.AVIATION /21Z TUESDAY THROUGH SUNDAY/...
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.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
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WINTER STORM WARNING UNTIL 7 PM EST WEDNESDAY FOR PAZ010>012-
017>019-024>028-033>036-041-042-045-046-049>053-056>059-
063>066.
WINTER WEATHER ADVISORY UNTIL 7 PM EST WEDNESDAY FOR
PAZ004>006-037.
-- End Changed Discussion --

&&

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