Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 291958 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 358 PM EDT WED OCT 29 2014 .SYNOPSIS... SHOWERS ASSOCIATED WITH AN EXITING FRONT WILL EXIT SOUTHEAST PENNSYLVANIA EARLY THIS EVENING. A POTENT SHORTWAVE WILL CARVE OUT A DEEP TROUGH OVER THE NORTHEAST CONUS AS IT DIVES ACROSS THE REGION LATE FRIDAY AND SATURDAY. THE UPPER TROUGH WILL LIFT OUT BY EARLY NEXT WEEK...REPLACED BY A RIDGE BUILDING ALONG THE EAST COAST. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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BACKING FLOW FINALLY ADVANCING THE BACK EDGE OF SHOWERS ACROSS THE LOWER SUSQ AT MID AFTERNOON. LATEST RADAR MOSAIC INDICATES STEADY SHOWERS WILL END OVER LANCASTER COUNTY BY 20Z...WITH ISOLATED SHOWERS PERSISTING UNTIL 23Z OR 00Z. A NARROW CORRIDOR OF CLEARING HAS REACHED INTO WESTERN PA AHEAD OF STRONGER BOUNDARY LAYER COOLING WHICH HAS INDUCED A LARGE STRATUS FIELD OVER SOUTHEAST OH AND NORTHWEST PA. APPROACHING UPPER TROF FROM THE CENTRAL GLAKS WILL SPREAD THICKER STRATUS SOUTHEAST OF LAKE ERIE LATER TONIGHT...AS 850 MB TEMPS COOL TO -2C BY 12Z THU. THERE COULD BE A SOME LIGHT SHOWERS OR SPRINKLES FOLLOWED BY A CHANCE OF FLURRIES BEFORE DAWN ACROSS THE NORTHWEST AS A RESULT...BUT NOT EXPECTING MUCH IN THE WAY OF QPF.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
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SHORTWAVE RIDGING AHEAD OF WEAK UPPER SHORTWAVES OVER THE OHIO VALLEY SHOULD PROVIDE A DRY DAY THROUGHOUT CENTRAL PA ON THURSDAY. THE DAY SHOULD START CLOUDY ACROSS THE NORTHWEST WITH A FEW SPRINKLES OR FLURRIES LINGERING INTO MID MORNING. LIKE EARLIER IDEA OF LAKE MOISTURE REMAINING TRAPPED BENEATH SUBSIDENCE INVERSION CAUSING A GOOD DEAL OF STRATOCU ACROSS THE ALLEGHENY PLATEAU...WHILE DOWNSLOPING NW FLOW YIELDS A BRIGHTER DAY ACROSS THE SUSQ VALLEY. ENS MEAN 925MB TEMPS SUPPORT MAX TEMPS FROM THE M40S ALLEGHENIES...TO M50S SUSQ VALLEY.
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&& .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
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THE BIG STORY THROUGH THE LONG TERM PERIOD REMAINS THE TRACK OF THE LARGE UPPER LEVEL LOW THAT WILL PROGRESS THROUGH THE GREAT LAKES REGION ON FRIDAY...AND ITS PROGRESSION EASTWARD THIS WEEKEND. ALL MEDIUM RANGE GUIDANCE STILL SHOWS A POTENT SHORTWAVE DIVING SE FROM CANADA AND CARVING OUT A DEEP TROUGH OVR THE NORTHEAST CONUS BY SATURDAY. THE GFS ENSEMBLES VARY ON THE STRENGTH AND POSITION OF THIS LOW...THROUGH ALL SHARE SIMILAR TIMING. THE OPERATIONAL GFS AND EC ARE IN LINE WITH ONE ANOTHER AND HAVE THE UPPER LOW DIG SOUTH OF THE REGION AND ACTUALLY MOVES THROUGH THE CAROLINAS BEFORE MOVING OFF COAST. THE EC HAS TRENDED TOWARDS THE GFS...AND BOTH HAVE THE LOW FURTHER EASTWARD INTO THE ATLANTIC BEFORE IT TRAVERSES NORTHWARD. THE ASSOCIATED SFC CLIPPER LOW IS PROGGED TO TRACK ACROSS EASTERN OHIO/WESTERN PA LATE FRIDAY AND FRIDAY NIGHT...BRINGING THE BEST CHANCE OF PRECIP TO THAT AREA. BOTH GEFS AND OPER ECMWF/CANADIAN MDLS ALL POINT TOWARD A MAINLY RAIN EVENT FRIDAY. HOWEVER...AS UPPER LOW CUTS OFF SOUTH OF PA EARLY SATURDAY...THERMAL PROFILES...COUPLED WITH MOIST EASTWARD UPSLOPE FLOW MAY BECOME COLD ENOUGH TO PRODUCE A LIGHT COATING OF SNOW ACROSS THE HIGH TERRAIN OF THE ALLEGHENIES. EXPECT A RAIN...SNOW MIX POSSIBLE THROUGH THIS TIMEFRAME...AND ANY SNOWFALL WILL BE WET. AS THE DEVELOPING COASTAL LOW MOVES UP THE COAST LATE SATURDAY...A TIGHTENING PRESSURE GRADIENT AND NW FLOW WILL DRAW MUCH COLDER/DRIER AIR INTO THE REGION. OPERATIONAL RUNS AND NEARLY ALL ENSEMBLE MEMBERS KEEP COASTAL LOW FAR ENOUGH OUT TO SEA TO NOT DIRECTLY IMPACT CENTRAL PA. HOWEVER...COLD NW FLOW MAY PRODUCE LAKE EFFECT SNOW SHOWERS ACROSS THE NW MTNS SATURDAY NIGHT...EARLY SUNDAY MORNING. ESPECIALLY GIVEN THE STRONG...MOIST 850MB FLOW. TEMPS THIS WEEKEND WILL ALMOST CERTAINLY BE THE COLDEST YET THIS SEASON. ENSEMBLE MEAN 8H TEMPS POINT TOWARD DAYTIME HIGHS FROM THE UPPER 30S OVR THE ALLEGHENIES TO THE 40S ELSEWHERE. THE COLDEST NIGHT OF THIS OUTBREAK WILL LIKELY BE SUNDAY NIGHT...WHEN SFC HIGH BUILDS OVR THE REGION. THOSE LOCATIONS THAT HAVE YET TO SEE A FREEZE WILL LIKELY GET IT BY MONDAY AM. HIGH CONFIDENCE IN A PERIOD OF DRY WEATHER SUNDAY/MONDAY...WHEN ALL GUIDANCE BUILDS SFC HIGH AND ASSOC DRY AIR MASS ACROSS PA. AN APPROACHING COLD FRONT WILL BRING THE NEXT CHC OF SHRA BY MIDWEEK.
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&& .AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
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MVFR AND LCL IFR CIGS WILL BECOME VFR ACROSS THE FAR SOUTHEAST BY MID EVENING AFTER RAIN SHOWERS END BY EARLY EVENING. VFR CONDITIONS ARE EXPECTED TONIGHT ACROSS THE RIDGE AND VALLEY REGION OF CENTRAL PA. LAKE STRATUS AND MVFR CIGS ARE EXPECTED ACROSS THE ALLEGHENY PLATEAU WITH SCT -SHRA AND PERHAPS FLURRIES BY 12Z ACROSS NORTHWEST MOUNTAINS. CONDS WILL BECOME MOSTLY VFR BY THU AFTERNOON. OUTLOOK... THUR...MVFR CIGS WEST EARLY...THEN VFR. VFR EAST. FRI...VFR/MVFR EARLY WITH SHOWERS POSS WEST...BCMG MVFR/IFR FRI NGT WITH NW WIND GUSTS 20-30 MPH AND RA/SN SHOWERS. SAT...MVFR/IFR WITH SCATTERED SNOW SHOWERS WEST. VARYING VFR- MVFR CONDS CENTRAL/EAST WITH OCNL -SHSN AND FLURRIES. NW WIND GUSTS 25-35 MPH. SUN...BECOMING VFR...WINDS DECREASING. MON...VFR.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...DEVOIR/FITZGERALD NEAR TERM...DEVOIR/FITZGERALD SHORT TERM...DEVOIR/FITZGERALD LONG TERM...CERU AVIATION...DEVOIR/LAMBERT

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