Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 210019 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 719 PM EST SAT DEC 20 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 7 AM SUNDAY MORNING/... CLOUDS CONGESTING OVER THE AREA BUT SOME AREAS STILL FREE OF THE LOWEST DECK. A VIGOROUS SHORT WAVE ROLLING OVERHEAD EARLY TONIGHT MAY CREATE ENOUGH LIFT AND COULD SEED THE LOWER CLOUDS WITH ICE CRYSTALS FROM ABOVE. THUS...SOME FLURRIES ARE EXPECTED OVER THE LAURELS AND ALONG THE NRN TIER. WILL LEAVE ACCUMS OUT OF THE FCST FOR NOW. MINS PROBABLY A HOMOGENEOUS 20-25F ACROSS THE BOARD. && .SHORT TERM /7 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/... 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. PRIOR TO THAT...SOME AREAS COULD PERHAPS SEE A FLURRY IN THE PRE DAWN HOURS SUNDAY BEFORE THE WAVE QUICKLY EXITS EASTWARD. WENT CLOSE TO CONSALL GUIDANCE AGAIN WITH MAXES REACHING THE MID TO UPPER 30S NORTH TO THE LOWER 40S SOUTH. && .LONG TERM /SUNDAY 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 /00Z 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. EXPECT THE EXPANDING STRATOCU DECK LIKELY TO RETURN AGAIN TONIGHT...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. 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 AND UNV...WITH IFR POSSIBLE AT BFD AND JST...WITH MAINLY VFR THROUGH THE EASTERN TAF SITES. 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...DANGELO SHORT TERM...FITZGERALD LONG TERM...GRUMM AVIATION...DEVOIR/CERU

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