Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 241809
AFDCTP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
109 PM EST MON NOV 24 2014

.SYNOPSIS...
NEAR-RECORD WARM TEMPERATURES ARE EXPECTED OVER MUCH OF THE AREA
TODAY...BEFORE COLD AIR ARRIVES TONIGHT BEHIND A DEPARTING LOW
PRESSURE SYSTEM. ANOTHER AREA OF LOW PRESSURE WILL MOVE ALONG THE
MID ATLANTIC COAST WEDNESDAY INTO THURSDAY... BRINGING A CHANCE OF
SIGNIFICANT SNOW TO THE EASTERN HALF OF PENNSYLVANIA. ANOTHER
SHOT OF COLD AIR WILL FOLLOW FOR NEXT WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
TEMPS WILDLY ABONORMAL WITH VERY STRONG LLVL JET ALOFT BRINING IN
WARM AIR AND MIXING BRINING DOWN THE HIGH POTENTIAL AIR. SUNSHINE
AND MORE SUN-TIME TO GO...SO WE WILL LIKELY CRACK A RECORD MAX OR
TWO. GUSTS NOT INTO THE 30S CONSISTENTLY YET...AND WIND ADVY LOOKS
WEAK. ONLY THE HIGHER PEAKS SHOULD SEE ANYTHING ABOVE 40 KTS. THE
EXCEPTION WOULD BE IF ONE OF THE CONVECTIVE CELLS WHICH WILL GRAZE
THE NRN TIER COULD MIX SOMETHING HIGHER DOWN. BUT...WHEN ANY GUSTS
DEAL WITH/HAPPEN IN/NEAR CONVECTIVE CELLS...WE USE SVR/S TO
HANDLE THOSE.

FRONT PUSHES THROUGH LATE THIS AFTN IN THE NW AND THIS EVENING
ACROSS THE REST OF THE AREA. DRYING SRLY FLOW - DEWPOINTS INTO THE
30S ON THE HIGHER PEAKS IN THE WEST AND VALLEYS IN WRN PA SHOULD
KEEP SHRA TO A MINIMUM S OF I-80. TEMPS SHOULD DROP NICELY
OVERNIGHT...REACHING INTO THE L/M30S IN THE NW BY 12Z.

&&

.SHORT TERM /TUESDAY/...
BOUNDARY LAYER FLOW WILL SLOWLY BACK AND WEAKEN ON TUESDAY...WHILE
A WEAK AREA OF HIGH PRESSURE DRIFTS INTO THE OHIO VALLEY AND INTO
THE WRN PA TUESDAY NIGHT. TUESDAY WILL BE THE CALM BEFORE THE
STORM AS ALL EYES SHIFT SOUTHWARD FOR THE EVOLUTION OF WHAT COULD
BE THE FIRST WIDESPREAD SIGNIFICANT SNOWFALL ACROSS MUCH OF THE
EASTERN HALF OF CENTRAL PA WEDNESDAY.

COLD AIR WILL CONTINUE TO FILTER IN ALOFT...AND HIGHS TUESDAY WILL
BE SOME 20 DEGREES COOLER THAN THE NEAR RECORD READINGS OF MONDAY
AFTERNOON.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
POTENTIAL FOR SIG WINTER IMPACTS FROM LOW PRESSURE MOVING UP THE
EAST COAST ON WED/WED NIGHT. WILL CONTINUE TO INJECT
INTERPRETATION OF THE LATEST MODEL GUIDANCE WITH EACH 3-HOURLY
UPDATE TO GUIDE DECISION SUPPORT LEADING UP TO THE PRIME TRAVEL
PERIOD FOR THE THANKSGIVING HOLIDAY.

HIGHLY AMPLIFIED AND ACTIVE UPPER AIR PATTERN WILL BRING A PERIOD
OF ACTIVE WEATHER THROUGH THE COMING WEEK. THE 500MB CONFIGURATION
WILL FEATURE ANOMALOUS RIDGING ALONG THE WEST COAST AND IN THE
WESTERN ATLANTIC WITH A FULL-LATITUDE PERSISTENT TROUGH EBBING
AND FLOWING OVER THE CENTRAL AND EASTERN U.S.

AFTER THE EXIT OF MONDAY/S LOW PRESSURE AREA...COLDER TEMPS
RETURN ON BRISK W/SW FLOW FOR TUE DROPPING HIGHS SOME 20-25F FROM
PREV DAYS READINGS. WE/LL ALSO SEE THE RETURN OF LIGHT SNOW
SHOWERS IN THE WESTERN HIGHER TERRAIN.

THEN FOCUS WILL TURN TO A WAVE CURRENTLY DROPPING SE FROM BRITISH
COLUMBIA AND WASHINGTON STATE...WHICH WILL SPAWN AN AREA OF LOW
PRESSURE OVER THE SE US TUESDAY NIGHT...THAT WILL LIKELY MOVE
NORTH NORTHEASTWARD JUST OFF THE EAST COAST WEDNESDAY INTO
THURSDAY.

12Z/18Z OPERATIONAL AND GEFS RUNS ALONG WITH THE 21Z SREF ARE
BECOMING FAIRLY WELL CLUSTERED WITH RESPECT TO THE LOCATION OF THE
NEAR...TO SUB-1000 MB SFC LOW EARLY WED EVENING /NEAR...AND UP TO
ABOUT 200 NM EAST OF DELMARVA PENINSULA/.

THERE IS STILL MUCH UNCERTAINTY AT THIS 60-72 HOUR TIMEFRAME
BEFORE THE EVENT...WITH RESPECT TO THE EXACT TRACK OF THE SFC LOW
AND ASSOCIATED SNOW/RAIN AMOUNTS.

COLD AIR WILL BE IN PLACE WED MORNING AS A /WEAK/ HIGH PRESSURE
RIDGE RETREATS TO THE NORTH AHEAD OF THE APPROACHING LOW.
NORTHERLY FLOW OVER CENTRAL PA NOT PARTICULARLY STRONG IN ANY
MODEL...BUT A SHORTWAVE LOOKS POISED TO SLIDE IN FROM THE GREAT
LAKES ON WED TO ADD SOME SYNOPTIC LIFT TO A RAPIDLY DEEPENING AND
FAST MOVING SURFACE LOW.

THE 12Z ECMWF AND IT`S ENSEMBLE ARE VERY SIMILAR HUGGING THE SFC
LOW ALONG THE SHORELINE...WHILE US/CANADIAN MODELS AND THEIR
ENSEMBLES ARE FURTHER EAST BY 100-200 NM. EXPERIENCE SHOWS THAT
THE LACK OF A SIGNIFICANT BLOCKING HIGH TO OUR NORTH OR
NORTHEAST...FAVORS A MORE WESTERN TRACK /SIMILAR TO THE EC AND ITS
ENSEMBLE/. SHOULD THE WWD TREND CONTINUE EVEN FURTHER WITH AN
EARLIER INJECTION OF NRN STREAM ENERGY INTO THE SOUTHERN STREAM
SYSTEM...IT/S CONCEIVABLE THAT OUR FAR SE ZONES /NEAR KLNS AND
KMDT/ COULD EVEN SEE A MIX WITH SLEET AND RAIN FOR A PERIOD THAT
WOULD HOLD DOWN ACCUMULATIONS.

PRECIP MAY START OFF EARLY WED AS A MIX OF RAIN AND SNOW IN THE
SE...BUT COOLING TEMPS ALOFT SHOULD CONVERT ALL PRECIP OVER TO
SNOW BY MIDDAY. AS IS A GENERAL RULE WITH THESE TYPES OF EVENTS...
THERE WILL LIKELY BE A SHARP DROP OFF IN ACCUMULATIONS ON THE NW
EDGE OF THE HEAVIER SNOWS. BIGGEST POTENTIAL IMPACTS IN OUR CWA
WILL BE THE CENTRAL MTNS AND SUSQ VALLEY...WHERE POTENTIAL FOR A
SEVERAL HOUR PERIOD OF HEAVY ACCUMULATING SNOW WILL EXIST. BUT
AGAIN...SMALL CHANGES IN THE ULTIMATE TRACK COULD LEAD TO
MODIFICATIONS OF SNOWFALL FORECASTS. THE TAKE AWAY...THOUGH THE
DETAILS REMAIN UNCERTAIN...THERE WILL BE SIG IMPACTS TO TRAVEL
ALONG THE U.S. EAST COAST ON ONE OF THE BUSIEST DAYS OF THE YEAR
/WED/. PLAN ACCORDINGLY.

COLDER AIR REMAINS IN PLACE LATE IN THE WEEK AS SCT SNOW SHOWERS
RETURN TO THE WESTERN HIGHER TERRAIN. TEMPS LOOK TO GRADUALLY
MODIFY LATE WEEKEND HEADING INTO NEXT WEEK...WITH NO BIG STORM
SYSTEMS EXPECTED AFTER THANKSGIVING.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
DEEP SYSTEM LIFTING NE.

STRONGEST WIND FIELDS LIFT NE THIS AFT.

TOOK OUT LLWS.

MAIN CONCERN IS LINES OF SHOWERS TO THE WEST. WILL CONTINUE TO
MONITOR...NO THUNDER AT THIS PT. NOT REAL COLD ALOFT...THUS NOT
CONCERN ABOUT DAMAGING WINDS AT THIS TIME.

WINDS WILL WEAKEN OVERNIGHT. DID NOT WEAKEN THEM TOO MUCH.
SHOULD THE WIND DIE AT SPOTS LIKE IPT...MDT...AND LNS...
THEN FOG COULD BE AN ISSUE. EXPECT DRIER AIR TO THE WEST.

LOOKING AT VFR CONDITIONS INTO EARLY TUE AFT...GIVEN
DIRECTIONAL SHEAR AND LIMITED COLD AIR.

MAIN CONCERN WILL BE WED...PERIODS OF WET SNOW EXPECTED...AS
A COMPLEX LOW LIFTS NE.

OUTLOOK...

TUE...NO SIG WX EXPECTED.

WED...SNOW/LOW VSBYS POSS EASTERN PA.

THU...-SHSN/REDUCED VSBYS POSS NW MTNS.

FRI...NO SIG WX EXPECTED.

SAT...NO SIG WX EXPECTED...AS HIGH PRESSURE BUILDS IN.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY UNTIL 4 AM EST TUESDAY FOR PAZ004>006-010-011-
017-024-033.

&&

$$
SYNOPSIS...DEVOIR
NEAR TERM...DANGELO
SHORT TERM...DEVOIR
LONG TERM...DEVOIR/RXR
AVIATION...MARTIN



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