-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KCTP 061256
AFDCTP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
756 AM EST FRI DEC 6 2013

.SYNOPSIS...
A SERIES OF LOW PRESSURE WAVES WILL TRACK NORTHEAST FROM THE
TENNESSEE VALLEY ACROSS THE MID-ATLANTIC STATES TODAY THROUGH
SATURDAY...BRINGING A CHANGEOVER TO MIXED AND FROZEN PRECIPITATION
TO THE AREA. HIGH PRESSURE WILL PROVIDE A BRIEF RESPITE IN THE
RECENTLY ACTIVE EARLY SEASON WINTER WEATHER PATTERN ON SATURDAY.
CONFIDENCE IS STEADILY INCREASING FOR A PERIOD OF FROZEN AND
FREEZING PRECIPITATION SUNDAY INTO EARLY MONDAY THAT SHOULD
EVENTUALLY CHANGE TO RAIN. AN ARCTIC FRONTAL PASSAGE EARLY NEXT
WEEK WILL DROP TEMPERATURES WELL BELOW NORMAL THROUGH NEXT
WEDNESDAY.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
COLD FRONT IS NOW PRESSING SOUTHEASTWARD ACROSS THE SOUTH CENTRAL
MOUNTAINS AND MIDDLE TO LOWER SUSQUEHANNA RIVER VALLEY AS OF 350
AM. TEMPERATURES HAVE DROPPED TO THE LOWER 30S ACROSS THE
NORTHWEST MOUNTAINS WHERE OCCASIONAL -FZRA HAS BEEN REPORTED AT
KBFD (AT +1C?). TO THE WEST...PERIODS OF SNOW HAVE BEEN REPORTED
ALL NIGHT AT KERI AND KHZY. PRECIPITATION SHIELD IS BREAKING UP
WITH A LULL IN THE ACTIVITY EVIDENT AS THE FRONTAL WAVE PUSHES
OFFSHORE AND THE UPSTREAM WAVE LAGS TO THE SOUTH OVR THE CENTRAL
APPALACHIANS.

WHILE PRECIPITATION FROM THE UPSTREAM WAVE WON`T BEGIN IN EARNEST
UNTIL THIS AFTERNOON...THE PATCHY FREEZING DRIZZLE ACROSS THE
NORTHWEST MOUNTAINS THIS MORNING NECESSITATES AN EARLIER START
TIME FOR THE WINTER WEATHER ADVISORY THERE. WILL RUN FROM THIS
MORNING INTO THE PREVIOUSLY ISSUED ADVISORY FOR THE AREA... WHICH
CONTINUES THROUGH SATURDAY MORNING.

FOR THE REMAINDER OF CENTRAL PA...THE COLDER AIR WILL SPREAD
SOUTHEASTWARD BUT AM NOT EXPECTING MUCH IN THE WAY OF FREEZING OR
FROZEN PRECIPITATION FOR MUCH OF THE DAY. ONSET OF STEADIER
PRECIPITATION THIS AFTERNOON AND EVENING WILL HELP CHANGEOVER TO
SLEET AND SNOW ACROSS MUCH OF THE LAURELS...AND THE CENTRAL AND
NORTHERN MOUNTAINS. WILL LIKELY EXPAND CURRENT ADVISORIES INTO THE
CENTRAL PA MOUNTAINS FOR SNOW AND SLEET ACCUMS LATE THIS AFTERNOON
AND EVENINGS AS OVERNIGHT GEFS AND SREF ARE DEPICT AVERAGE/MEDIAN
SNOW AND SLEET QPF IN THE .5 TO .65" RANGE. EVEN A 5 TO 1 RATIO
PUTS MOST OF THE AREA IN ADVISORY RANGE...SO THE EXPANSION WILL BE
WARRANTED. KEPT ALL PREVIOUS HEADLINES AS IS.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
MODERATE PRECIPITATION SHIELD ASSOCIATED WITH THE LAST IN A SERIES
OF SFC WAVES RIPPLING ALONG THE FRONTAL ZONE WILL BRING A
WIDESPREAD WINTRY SHOT OF PRECIPITATION TO CENTRAL PA. NEAR TO
SHORT TERM GUIDANCE IS POINTING MORE TOWARDS SNOW AND SLEET WITH
THIS FEATURE LATE THIS AFTERNOON AND EVENING...WITH A FEW TO
SEVERAL INCHES OF SNOW AND SLEET LIKELY FOR MUCH OF CENTRAL PA
EXCLUDING SOUTHERN AND EASTERN PORTIONS OF THE SOUTH CENTRAL
MOUNTAINS AND THE MIDDLE TO LOWER SUSQ. PRECIP ACROSS THE MIDDLE
TO LOWER SUSQ MAY CHANGE TO SNOW BEFORE ENDING SATURDAY MORNING
WITH LIGHT IF ANY ACCUMS.

SIMILAR TO PREVIOUS MODEL RUNS...BLENDED MDL QPF SUPPORTS A 3-5
INCH SNOWFALL ACROSS THE N TIER. LATEST GUIDANCE SUGGESTS MORE
DRAMATIC CHANGEOVER BY THIS EVENING ACROSS THE CENTRAL COUNTIES
FOR ADVISORY CRITERIA SNOW/SLEET TO FALL. AS PREVIOUSLY MENTIONED...
WILL BE EXPAND WINTER WEATHER ADVISORIES AND UPDATE SNOWFALL MAPS
FOR THIS SHORTLY (BEFORE 6 AM FRI)

DEEPENING COLD AIR WILL ADVECT INTO THE STATE LATE TONIGHT WITH
LINGERING LIGHT SNOW/MIXED PRECIP TAPERING OFF BY 12Z SAT. WITH
COLD HIGH PRESSURE BUILDING EASTWARD ACROSS THE UPPER MIDWEST AND
NNW FLOW PREVAILING SATURDAY ACROSS CENTRAL PA...WILL SEE THE
TRADITIONAL POST FRONTAL STRATUS PERSIST ACROSS THE NORTH AND WEST...
WHILE FAR SOUTH AND SOUTHEASTERN AREAS ENJOY PARTIAL CLEARING AND
SUNBREAKS FOR MOST OF THE AFTERNOON.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
1040+ MB MODIFIED ARCTIC SFC HIGH PRESSURE OVER THE UPPER MIDWEST
SATURDAY WILL MIGRATE EASTWARD INTO THE NORTHERN MID-ATLANTIC
STATES BY SUNDAY MORNING...SETTING THE STAGE FOR WHAT APPEARS TO
BE A CLASSIC OVERRUNNING MIXED PRECIP EVENT FOR LATER SUNDAY INTO
MONDAY.

05/12Z DETERMINISTIC MODEL AND ENSEMBLE GUIDANCE SHOWS LOW PRES
INITIALLY DEVELOPING ALONG AN INVERTED SFC TROUGH AXIS EXTENDING
FROM THE LWR MS/TN VLY NEWD UP THE WEST-SIDE OF THE APPALACHIANS.
THE MAIN LOW SHOULD LIFT NWD THRU THE OH VLY/GRT LKS INTO SERN
CANADA ON DAYS 5-6. MEANWHILE A SECONDARY/WEAKER AREA OF LOW PRES
SHOULD FORM NEAR THE VA/NC COAST AND TRACK NNEWD JUST OFFSHORE SRN
NEW ENGLAND.

DOWNSTREAM FROM A VIGOROUS MID/UPPER LEVEL TROUGH DIGGING THROUGH
THE FOUR CORNERS/SRN ROCKIES...A SURGE OF INTENSE 850-700MB WARM
AIR/THETA E/MOISTURE ADVECTION WILL SPREAD QUICKLY NEWD BEHIND A
BROAD SWLY FLOW ALOFT AND OVERRUN A RETREATING COLD SECTOR
ASSOCIATED WITH THE RETREATING ARCTIC HIGH. THE SYNOPTIC PATTERN
LOOKS VERY CONDUCIVE FOR A PERIOD OF FREEZING-TO-FROZEN PCPN AS
MSTR AND STG WAA ALOFT FLOWS OVER THE TOP OF A SHALLOW SUB-FZG
AIRMASS THAT SHOULD REMAIN ENTRENCHED ALONG/E OF THE ALLEGHENIES
VIA LLVL COLD AIR DAMMING/SFC PRES CHANNELING...ENHANCED BY NELY
AGEO FLOW AND WET BULB EFFECTS. SFC-850MB TEMPS ARE FCST TO WARM
ENOUGH TO CHANGE FREEZING PTYPES TO PLAIN RAIN IN MOST AREAS
AROUND MON AFTN BEFORE THE ARCTIC COLD FRONT CROSSES THE REGION
MON NGT. THE 12Z GEFS MEAN SHOWS A HIGH PROBABILITY OF A FEW
INCHES OF SNOW/SLEET ON THE LEADING EDGE OF THE PRECIP SHIELD
FOLLOWED BY POTENTIAL SIGNIFICANT ICE ACCUMS ESPECIALLY FROM THE
LAURELS/SCNTRL MTNS INTO THE INTERIOR N-CNTRL PART OF THE CWA.
WILL CONTINUE TO HIGHLIGHT THIS SYSTEM IN THE HWO BUT CONFIDENCE
IS INCREASING IN AT LEAST AN ADVISORY TYPE EVENT...IF NOT WARNING
ASSUMING MOD-HVY ICING VIA FZRA.

IN THE WAKE OF THIS SYSTEM...A VERY COLD PATTERN SHOULD GRIP THE
REGION THRU THE MIDDLE OF NEXT WEEK WITH TEMPERATURES WELL BELOW
NORMAL. SOME LAKE EFFECT SNOW SHOWERS ARE POSSIBLE IN THE COLD
CYC FLOW ALOFT ALTHOUGH THE LLVL WINDS MAY HAVE TOO MUCH OF A SW
COMPNT WHICH WOULD ORIENT BANDS MORE ALONG THE LAKE ERIE SHORE
INTO SW NY.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...

-- Changed Discussion --
SHOWERS CONTINUE TO STREAM ACROSS SOUTHERN AND CENTRAL PA WITH
LIGHT MIXED PRECIPITATION OVER JST AND BFD. THIS STEADY WAVE OF
RAIN MOVING THROUGH CENTRAL PA AND THE LOWER SUSQ WILL CONTINUE THROUGH
THE MORNING. CIGS FOR MOST TAF SITES HAVE LIFTED TO MVFR...AND
WILL REMAIN AROUND MVFR THROUGH THE MORNING AND EARLY AFTERNOON.
JST CURRENTLY HAS LIFR CIGS AND WILL SEE THESE CONTINUE THROUGH
THE MORNING AND EARLY AFTERNOON BEFORE SLIGHTLY LIFTING. THESE
WILL BE MVFR AND LOWER THROUGH TONIGHT. EXPECT THE MIXED
PRECIPITATION TO SWITCH TO RAIN THROUGH THE AFTERNOON HOURS
BEFORE SWITCHING TO A WINTRY MIX LATE THIS AFTERNOON AND SWITCHING
TO SNOW TONIGHT. EXPECT IFR CIGS AND VSBYS TO CONTINUE TONIGHT
INTO EARLY TOMORROW. MOST TAF SITES SHOULD BEGIN TO CLEAR EARLY
TOMORROW MORNING.


OUTLOOK...

FRI...MVFR IN RAIN SE. IFR IN SNOW/WINTRY MIX NW.

SAT...MVFR SNOW SHOWERS IN THE MOUNTAINS. VFR IN CENTRAL/EASTERN
AREAS.

SUN...REDUCTIONS DEVELOPING WITH APPROACHING STORM THAT WILL BRING
A WINTRY MIX SPREADING SOUTH TO NORTH INTO SUN NIGHT.

MON...WIDESPREAD MVFR/IFR ASSOCIATED WITH A PASSING COLD FRONT.
-- End Changed Discussion --

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 5 AM EST SATURDAY FOR PAZ004>006-
010-011.
WINTER WEATHER ADVISORY FROM 1 PM THIS AFTERNOON TO 5 AM EST
SATURDAY FOR PAZ012-017-018-037-041-042.
WINTER WEATHER ADVISORY FROM 5 PM THIS AFTERNOON TO 5 AM EST
SATURDAY FOR PAZ019-024-025-033-045-046.

&&

$$
SYNOPSIS...DEVOIR
NEAR TERM...DEVOIR
SHORT TERM...DEVOIR/LA CORTE/STEINBUGL
LONG TERM...STEINBUGL
AVIATION...CERU/GARTNER