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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KCTP 180319
AFDCTP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
1019 PM EST TUE DEC 17 2013

.SYNOPSIS...
A WEAK TROUGH OF LOW PRESSURE WILL SWING THROUGH TONIGHT...
ACCOMPANIED BY LIGHT SNOW AND A GUSTY WEST SOUTHWEST WIND. A
GRADUAL WARM-UP WILL BEGIN THURSDAY AND PEAK SUNDAY WHEN
TEMPERATURES SHOULD TOP OUT 15 TO 20 DEGREES ABOVE NORMAL. A SLOW
MOVING COLD FRONT WILL BRING PERIODS OF RAIN FRIDAY AFTERNOON
THROUGH SUNDAY. COLDER AIR WITH MAINLY MOUNTAIN SNOW SHOWERS WILL
FOLLOW FOR MONDAY AND TUESDAY. AT THIS POINT...CHRISTMAS DAY LOOKS
DRY WITH SEASONABLY COLD TEMPERATURES.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
CLEAR SLOT IN BETWEEN DEPARTING SYSTEM AND THE TROUGH OVER WRN PA
IS ALLOWING THE TEMPS TO DROP QUICKLY OVER THE EASTERN COUNTIES.
HAVE ADJUSTED FOR THIS CHANGE. BUT STILL BRING THEM BACK TO NEAR
WHERE PREVIOUS MINS WERE BY THE END OF THE NIGHT...SINCE THE
CLOUDS AND A LITTLE WIND SHOULD HELP MIXING AND INSULATION/RE-
RADIATION.

IMMEDIATELY PREVIOUS...
TROUGH IS WELL-TIMED AND POSITIONED. VERY MINOR SNOW ACCUMS
EXPECTED IN THE WRN MTS...AND BARELY A DUSTING ELSEWHERE. CLOUDS
MAY KEEP THE TEMPS UP A LITTLE OVERNIGHT...BUT HAVE MADE ALMOST
NO CHANGES TO THE FCST AT THIS UPDATE.

PREVIOUS...
THE BACK EDGE OF STEADY LIGHT...AND OCNLY MDT SNOW WILL EXIT OUR
FAR SERN ZONES BY 21Z...LEAVING PLENTY OF LOW...NON-PRECIPITATING
CLOUDS WITH 3-5SM HAZE AND LIGHT WIND ACROSS THE EASTERN HALF OF
THE CWA INTO THIS EVENING ACROSS THE EASTERN HALF OF PENN.

FLURRIES AND SCATTERED MTN SNOW SHOWERS WILL DEVELOP LATE TODAY AND
TONIGHT ACRS THE LAURELS AND NW MTNS...IN THE WAKE OF AN OCCLUDED
FRONT THAT WAS DRIFTING SLOWLY EAST ACROSS THE CENTRAL MTNS AT 20Z.

AS AN UPPER TROUGH AXIS /WITH 500 MB TEMPS OF -35 TO -37C/ AND MID
LEVEL LAPSE RATES APPROACHING 7.5C/KM...SWINGS THRU THE AREA TONIGHT
EXPECT LG SCALE FORCING TO SUPPORT A GOOD CHC OF SHSN ACROSS THE W
MTNS.

PAINTED SOME MINOR ACCUMS OF AN INCH OR SO ACROSS THE LAURELS TNGT
INTO WED...AND A LITTLE MORE ACROSS THE NW MTNS WHERE HIGH RES
SIMULATED RADAR REFLECTIVITY AND MEAN BLYR FLOW FROM THE WEST
SUPPORTS ONE OR TWO LES BANDS NIPPING NWRN WARREN COUNTY AND PERHAPS
NRN MCKEAN CTY BEGINNING LATE TONIGHT. PRIOR TO THAT TIME...THE MORE
ORGANIZED/SIGNIFICANT LAKE EFFECT SNOWS WILL BE AIMED ALONG...OR TO
THE NORTH OF THE I-90 CORRIDOR.

TEMPS ARE ACTUALLY A FEW DEG F HIGHER BEHIND THE OCCLUDED FRONT AND
WILL STAY NEARLY STEADY ACROSS THE NRN AND WRN MTNS...AND SHOULD
CLIMB BY ANOTHER 3 OR 4F ACROSS THE SUSQ VALLEY FOR A LATE
AFTERNOON/EARLY EVENING HIGH OF 30-32F.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
THE COLD...AND FAIRLY WELL-ALIGNED WESTERLY FLOW OVR LK ERIE WILL
LIKELY SUPPORT A SINGLE BAND INTO SOUTHWESTERN NY STATE FOR MUCH OF
THE TIME WEDNESDAY. THIS SNOWBANDS COULD SNEAK JUST SOUTH OF THE
BORDER AT TIMES DURING THE MORNING AND MIDDAY HOURS
WEDNESDAY...BRINGING SOME LIGHT ACCUMS OF 1-3 INCHES TO MAINLY THE
NW HALF OF WARREN CTY AND NRN MCKEAN CTY.

DECIDED TO STILL HOLD OFF ON A LES ADVISORY...AS LATEST MDL DATA
CONTINUES TO KEEP THE MORE SIGNIFICANT SNOW JUST NORTH OF THE
BORDER. IT WILL BE A CLOSE CALL...SO ANY LATER TENDENCY FOR MODELS
TO PUSH THE BANDS A LITTLE FURTHER SOUTH SHOULD FUEL CONSIDERATION
OF A LES ADVISORY FOR ONE OR TWO OF OUR NW SNOWBELT ZONES.

TIGHTENING PRESSURE GRADIENT BTWN HIGH PRES OVR THE SERN STATES AND
THE RAPIDLY INTENSIFYING LOW E OF NEW ENG WILL CREATE A BRISK WEST
WIND WEDNESDAY ACROSS ALL OF CENTRAL PA WITH GUSTS BTWN 22-27KTS PER
LATEST BUFKIT SOUNDINGS. 17/12Z ENS MEAN 8H TEMPS SUPPORT HIGHS
SEVERAL DEG BLW NORMAL...RANGING FROM THE M20S W MTNS...TO THE M30S
ACROSS THE LOWER SUSQ VALLEY WHERE DOWNSLOPING NW FLOW SHOULD YIELD
PTSUNNY SKIES.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
PREDOMINATELY ZONAL FLOW WILL DOMINATE THE SECOND HALF OF THE WEEK
AS THE MEDIUM RANGE GUIDANCE IS IN RELATIVELY GOOD AGREEMENT INTO
THE UP COMING WEEKEND. ALL OF WHICH SHOWS A DEEPENING
TROUGH...BECOMING A CUT OFF LOW...OVER THE WESTERN CONUS AND
THE DEVELOPMENT OF AN ANOMALOUS UPPER LEVEL RIDGE OFF OF THE EAST
COAST. AT THE SFC...BULK OF GUIDANCE DRAPES A QUASI- STATIONARY
FRONT FROM THE S PLAINS NE THRU THE EASTERN GRT LKS. WAVES OF LOW
PRESSURE RIDING WEST OF PA LATE FRIDAY AND SUNDAY WILL KEEP BRING THE
CHC OF RAIN TO MAINLY THE NW COUNTIES AND KEEP THE ENTIRE CWA ON
THE WARM SIDE OF THE BNDRY. THE MODELS DIVERGE INTO SUNDAY AND
TIMING IS VARIED SO HAVE LOWERED QPF SLIGHTLY...AND HAVE SPREAD IT
TO THE CENTRAL MOUNTAINS BASED ON FLOW. THE MODELS CONTINUE TO
SHOW A WARMING TREND WITH GEFS PLUMES INDICATING SUNDAY SHOULD BE THE
WARMEST DAY. THE SECOND AND STRONGER WAVE LIFTS WEST OF PA THROUGH
THIS TIMEFRAME...WITH COLD AIR BEHIND THE FRONT. THIS TRAILING
COLD FRONT SHOULD BRING A RETURN TO COOLER WX BY NEXT MONDAY INTO
TUESDAY.

&&

.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --
A WEAK PRESSURE GRADIENT ACROSS CENTRAL AND EASTERN PENN WILL
MAINTAIN LIGHT WINDS AND MVFR VSBYS IN FOG/HAZE INTO THE
OVERNIGHT...BEFORE A LIGHT WESTERLY WIND AND SOME DRIER AIR
SHOULD ALLOW FOR SOME IMPROVEMENT LATE. IPT AND LNS HAVE BEEN
FLIRTING WITH IFR VSBYS...WHICH MAY CONTINUE FOR THE NEXT FEW
HOURS.

ACROSS THE WESTERN TAF SITES /JST AND BFD/...ANOTHER DISTURBANCE
WILL BRING SCT SHSN INTO THE AREA OVERNIGHT. AN UPSLOPING WNW
FLOW WILL DEVELOP AS WELL...KNOCKING CIGS/VSBYS DOWN WITH
CONTINUED SHSN ACTIVITY.

WNW WINDS WILL BECOME BRISK ON WEDNESDAY...AS THE PRESSURE
GRADIENT TIGHTENS BETWEEN DEEPENING LOW PRES OVER THE CANADIAN
MARITIMES AND HIGH PRES OVER THE SERN US. EASTERN TAF SITES
SHOULD IMPROVE TO GENERALLY VFR CONDS ON WED...IN THE DOWNSLOPING
WNW FLOW. EVEN JST AND BFD WILL EVENTUALLY SEE SOME IMPROVEMENT
/TO AT LEAST MVFR/ AS THE DAY PROGRESSES.

AFTER A QUIET THURS...A DEVELOPING MOIST SOUTHERLY FLOW WILL TURN
THINGS UNSETTLED FRI INTO THIS WEEKEND.

OUTLOOK...

WED...SHSN AND REDUCED CIGS/VSBYS EARLY ACROSS THE WESTERN MTNS
/BFD AND JST/...WITH GRADUAL IMPROVEMENT. BECOMING VFR ELSEWHERE.

THU...GENERALLY VFR.

FRI-SUN...REDUCED CONDS LKLY AS ABUNDANT MOISTURE AND MILDER AIR
STREAMS NEWD AHEAD OF A SLOW-MOVING FRONTAL SYSTEM.
-- End Changed Discussion --

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$
SYNOPSIS...LAMBERT
NEAR TERM...DANGELO/LAMBERT
SHORT TERM...LAMBERT
LONG TERM...FITZGERALD/CERU
AVIATION...EVANEGO