Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 210641
AFDCTP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
141 AM EST SUN DEC 21 2014

.SYNOPSIS...
AN AMPLIFYING UPPER RIDGE WILL MOVE INTO THE REGION ON
SUNDAY. TEMPERATURES WILL THEN BECOME JUST SLIGHTLY MILDER BUT
UNSETTLED CONDITIONS WILL BEGIN ON MONDAY NIGHT AND PREVAIL
THROUGH MID WEEK. A VIGOROUS STORM SYSTEM WILL SWEEP ACROSS THE
COMMONWEALTH ON CHRISTMAS EVE BRINGING WIDESPREAD SHOWERS AND A
CHANCE FOR THUNDERSTORMS. WINDY AND COLDER CONDITIONS WILL FOLLOW
WITH SCATTERED SNOW SHOWERS ACROSS THE WEST AND NORTH FOR
CHRISTMAS DAY. MILDER CONDITIONS WILL RETURN LATE THIS WEEK.

&&

.NEAR TERM /UNTIL 8 AM THIS MORNING/...
STRATOCU REMAINS TRAPPED BENEATH SHARP INVERSION EARLY THIS
MORNING ACROSS CENTRAL PA. DEEPER MOISTURE AND LIFT ASSOC WITH
PASSAGE OF SHORT WAVE COULD PRODUCE SEEDER-FEEDER EFFECT WITH
LOWER CLOUDS...RESULTING IN A FEW FLURRIES ACROSS THE N MTNS BTWN
06Z-09Z. UNDER OVERCAST SKIES...TEMPS NOT EXPECTED TO FALL MUCH
MORE TONIGHT...BOTTOMING OUT IN THE LOW TO MID 20S MOST PLACES.

&&

.SHORT TERM /8 AM THIS MORNING THROUGH 6 PM MONDAY/...
DEEP LAYER DRYING BEHIND A DEPARTING 5H WAVE AND UPPER LEVEL
RIDGING HAS THE POTENTIAL TO BRING SUNSHINE TO MOST IF NOT ALL OF
CENTRAL PA ON MONDAY. THE STUBBORN STRATUS THAT HAS PLAGUED US FOR
MORE THAN A WEEK WILL HAVE A CHANCE TO MIX OUT...BUT TRANSITORY
SFC HIGH PRESSURE MAY STILL MAKE THIS A SLOW PROCESS OVER THE
NORTH.

WENT CLOSE TO CONSALL GUIDANCE AGAIN WITH MAXES REACHING THE LOW
30S OVER THE ALLEGHENIES TO THE UPPER 30S ACROSS THE LOWER SUSQ
VALLEY.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
THE MOST SIGNIFICANT FORECAST ISSUE IN THE LONG TERM IS THE
EVOLUTION OF THE MASSIVE CYCLONE TO OUR WEST 23-25 DECEMBER.
STRONG SOUTHERLY FLOW AHEAD OF THIS SYSTEM WILL BRING WARM AIR
INTO THE REGION LATE MONDAY INTO TUESDAY. BY TUESDAY AND WEDNESDAY
MANY LOW- LEVEL TEMPERATURE AND MOISTURE FIELDS WILL BE WELL ABOVE
THEIR SEASONAL VALUES. THIS IMPLIES VERY WARM WEATHER TUESDAY AND
WEDNESDAY...WHEN THE SHALLOW COLD AIR SCOURS OUT EAST OF THE
MOUNTAINS.

A COLD FRONT WITH STRONG WINDS WILL PRODUCE COLDER
CONDITIONS...LIKELY LATE CHRISTMAS EVE INTO CHRISTMAS DAY. THERE
WILL BE STRONG WESTERLY WINDS AND STRONG WIND GUSTS. SNOW SHOWERS
ARE LIKELY BEHIND THE SYSTEM IN WESTERN AREAS.

THE CHANGEABLE DETAILS...MONDAY THE ENSEMBLE FORECAST SHOWS A
WAVE PASSING TO OUR SOUTH WHICH COULD PRODUCE LIGHT SNOW OR A
MIX...MAINLY IN SOUTHEASTERN AREAS. THE IMPLIED LOW-LEVEL BOUNDARY
IS THE RETREATING COLD AIR TO OUR NORTHEAST AS THE STRONG CYCLONE
TO OUR WEST BEGINS TO TAKE SHAPE. IMPLIED LOW-LEVEL AGEOSTROPHIC
NORTHERLY FLOW HOLDING LOW-LEVEL COLD AIR IN MONDAY INTO TUESDAY.

TUESDAY THE COLD AIR SHOULD CONTINUE TO ERODE. HAD TO KEEP SOME
FREEZE RAIN/DRIZZLE IN NORTHEASTERN AREAS OVERNIGHT MONDAY INTO
TUESDAY BASED ON IMPLIED AGEOSTROPHIC FLOW AND ENSEMBLE
PRECIPITATION TYPES. BUT DURING THE DAY TUESDAY THE WARM AIR
SHOULD WIN OUT. THOUGH ALL SYSTEMS SHOW SOME HINTS OF COLD AIR
DAMMING....DAYTIME HIGHS EAST/NORTHEAST AREAS WILL BE WELL BELOW
WHAT ONE MIGHT EXPECT WITH 6-10C 850 MB TEMPS.

ANY PRECIPITATION TUESDAY AND WEDNESDAY SHOULD BE RAIN MUCH AFTER
NOON TUESDAY IN THE NORTHEAST. PRECIPITATION ON TUESDAY SHOULD BE
LIGHT...ENSEMBLES SHOW PROBABILITIES IN THE 20-30 RANGE AND LIGHT
AMOUNTS. THE PATTERN...SHARP NORTH-SOUTH FRONT TO OUR
WEST...IMPLIES SOME ISOLATED SHOWERS BUT THE MAIN RAIN EVENT
SHOULD WITHIN 3-6 HOURS OF THE FRONT.

TUESDAY THE STRONG CYCLONE...WITH SOME OF THE LOWEST SURFACE
PRESSURES IN THE EASTERN US ON 24 DECEMBER IN THE PAST 30 YEARS
WILL MOVE INTO THE GREAT LAKES. PRESSURE ANOMALIES ARE -3 TO -4
SIGMA BELOW NORMAL WITH A RETURN PERIOD ON THE ORDER OF 30 YEARS
IN SOME FORECAST SYSTEMS.

THE FRONT ASSOCIATED WITH THE CYCLONE PUSHES INTO OUR REGION
WEDNESDAY...AT THIS TIME THE 850 MB SOUTHERLY WINDS ARE FORECAST
TO BE ABOUT +3 SIGMA ABOVE NORMAL. THE STRONG SOUTHERLY FLOW...THE
HIGH PRECIPITABLE WATER...THE STRONG FRONT ALL IMPLY A FRONTAL
RAIN EVENT AND PERHAPS SOME RARE LATE DECEMBER (ELEVATED)
CONVECTION. IF THIS WERE AUTUMN OR SPRING WE MIGHT BE THINKING
QLCS. BUT SURFACE CAPE IS VIRTUALLY NON-EXISTENT BUT SHOWERY RAIN
AND PERHAPS ISOLATED THUNDER POSSIBLE.

DO NOT LIKE HAVING POPS ABOVE 60 TO 66 PERCENT AT DAY 5 IN 12 HOUR
PERIODS. TIMING WILL CLEARLY CHANGE BUT HAVE HIGH POPS FOR
CONSISTENCY WITH OTHER OFFICES.

CHRISTMAS EVE AND EARLY CHRISTMAS IS THE AREA OF HIGH UNCERTAINTY
AS TO WHEN THE COLD AIR COMES IN. THIS WILL DICTATE WHEN THE RAIN
COMES AND WHEN THE GUSTY WINDS SET IN. GRADIENTS ARE WHERE
FORECASTS ARE THEIR POOREST. BUT BY CHRISTMAS MORNING MOST IF NOT
ALL OF THE REGION SHOULD BE BELOW 0C AT 850 AND THE STRONG
WESTERLY WINDS SHOULD BE MIXING DOWN BEHIND THE FRONTAL BOUNDARY.
WINDY OVERNIGHT CHRISTMAS EVE INTO CHRISTMAS DAY. ANY RESIDUAL
PRECIPITATION SHOULD BE SNOW/SNOW SHOWERS AND FLURRIES.

TEMPERATURES SHOULD REBOUND FRIDAY AHEAD OF ANOTHER NORTHERN STREAM
WAVE MOVING INTO THE MID-WEST. THIS SHOULD RAISE OUR HEIGHTS AND
TEMPERATURES FRIDAY INTO EARLY SATURDAY. IT APPEARS A SERIES OF
WAVES MAY EVENTUALLY CARVE OUT A TROUGH OVER THE EAST-CENTRAL US. IF
SO...WE COULD END DECEMBER A BIT ON THE CHILLY SIDE.

&&

.AVIATION /07Z SUNDAY THROUGH THURSDAY/...
A WEAK AND SHALLOW STRATOCU DECK REMAINS TRAPPED BENEATH
SUBSIDENCE. THE CIG RESTRICTIONS WILL SPREAD AND INCREASE DUE TO
THE STRENGTHENING OF THE INVERSION OVERNIGHT...THOUGH LOW CLOUDS
SHOULD NOT BE QUITE AS EXPANSIVE AS PREVIOUS NIGHTS. A SHORTWAVE
WILL TRACK ACROSS THE REGION BRINGING A THICKENING MID- LVL DECK
AS WELL. THAT MID DECK WILL DECREASE THE PROBABILITY FOR A THICKER
LOW DECK. THE SURFACE WINDS WILL CONTINUE TO BE LIGHT...WITH SW
FLOW ALOFT BEGINNING TO INCREASE AS A LARGE LOW PRESSURE SYSTEM
BEGINS TO DEEPEN OVER THE CENTRAL U.S. EXPECT MVFR CIGS AT THE
CENTRAL SITES AOO...JST AND UNV. IFR REMAINS POSSIBLE AT JST
BETWEEN 09 TO 13Z...AND BFD SHOULD BE IFR THROUGH MOST OF THE
PERIOD. MAINLY VFR THROUGH THE EASTERN TAF SITES.
 BFD SHOULD LIFT TO MVFR BY LATE TOMORROW MORNING...THOUGH MVFR
SHOULD REMAIN POSSIBLE AT BFD THROUGH TOMORROW...AND IFR RETURNING
AT BFD TOMORROW EVENING.

OUTLOOK...

SUN...NO SIG WX EXPECTED.

MON...LOW CIGS WITH LGT RAIN/SNOW POSSIBLE. BECOMING BREEZY.

TUE...LOW CIGS WITH RAIN LIKELY. BREEZY.

WED...MILD WITH PERIODS OF RAIN OF VARYING INTENSITY...LEADING TO
MVFR TO IFR. ALSO...WINDY WITH LLWS.

THU...WINDY AND COLDER WITH SCT MVFR CIGS AND -SHSN.

&&

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

&&

$$
SYNOPSIS...DANGELO
NEAR TERM...FITZGERALD
SHORT TERM...DEVOIR
LONG TERM...GRUMM
AVIATION...DEVOIR/CERU


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