Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 250047 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 747 PM EST WED DEC 24 2014 .SYNOPSIS... AN INTENSIFYING STORM SYSTEM WILL MOVE UP THROUGH THE EASTERN GREAT LAKES THIS EVENING...DRAGGING A COLD FRONT THROUGH THE REGION OVERNIGHT. GUSTY WEST WINDS WILL DEVELOP BEHIND THE FRONT LATE TONIGHT AND THURSDAY. ANOTHER LESS POTENT COLD FRONT WILL MOVE ACROSS THE AREA THIS WEEKEND. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... EARLIER RAIN HAS SHIFTED EAST OF THE AREA WITH AXIS OF LL JET AND PLUME OF HIGHEST PWATS. LOOP OF SATL-DERIVED PWATS SHOW THIS ATMOSPHERIC RIVER...WITH ORIGINS OVR THE GULF OF MEX...PUSHING JUST OFF THE E COAST AS OF 00Z. FOCUS IS NOW ON SHARP COLD FRONT APPROACHING FROM THE WEST. WATER VAPOR LOOP SHOWS UPPER LVL SHORTWAVE LIFTING NE THRU LOWER MICHIGAN EARLY THIS EVENING. GIVEN THIS TRAJECTORY...EXPECT BULK LG SCALE FORCING TO PASS NORTH OF PA. THUS...SVR WX THREAT FROM APPROACHING SQUALL LINE SHOULD BE LIMITED TO THE NW MTNS...WHERE COMBINATION OF SOME MEAGER CAPE AND STRONG FORCING IS EXPECTED. LATEST HRRR OUTPUT SUGGEST THE THREAT WINDOW WILL BE BTWN 02Z- 04Z ACROSS THE NW COUNTIES. A MORE STABLE AIR MASS ACROSS THE REST OF CENTRAL PA WILL LIKELY PRECLUDE SVR WX. HOWEVER...COLD FRONT WILL BE ACCOMPANIED BY SHOWERS OVR MOST OF THE AREA LATER TONIGHT. HAVE PLACED THE HIGHEST POPS ACROSS THE SUSQ VALLEY...WHERE POSITIVE PWAT ANOMALIES THE HIGHEST. IT WILL BE AN UNSEASONABLY MILD CHRISTMAS EVE...AS THE REGION REMAINS WITHIN DEEP SOUTHERLY FLOW AHEAD OF GRT LKS LOW PRES SYSTEM. AREAS OF DRIZZLE AND FOG WILL PRECEDE THE ARRIVAL OF THE FRONTAL SHOWERS...WHICH SHOULD ARRIVE OVR THE SUSQ VALLEY JUST AFTER MIDNIGHT. THE COLD FRONT SHOULD BE ENTERING THE ALLEGHENY PLATEAU ARND 02Z-03Z AND EXITING THE SUSQ VALLEY DURING THE PRE-DAWN HOURS. BEST CHC OF THUNDER WILL BE ACROSS THE NW MTNS CLOSEST TO PATH OF MID LVL SHORTWAVE. HOWEVER...CAN/T COMPLETELY RULE OUT A RUMBLE FURTHER SE WITH FROPA. ALTHOUGH THE GREATEST THREAT OF SVR WX WILL BE ACROSS THE NW MTNS...SOME FAIRLY STRONG GUSTS WILL MIX TO THE SFC IMMEDIATELY FOLLOWING FRONTAL PASSAGE OVERNIGHT. LATEST BUFKIT SOUNDINGS SUPPORT GUSTS TO BTWN 40-45KTS OVR THE ALLEGHENY PLATEAU...WITH SLIGHTLY LOWER GUST POTENTIAL FURTHER EAST. STEADY OR SLOWLY RISING TEMPS EXPECTED OVERNIGHT UNTIL FRONT ARRIVES. BY DAWN...THE FRONT WILL HAVE CLEARED THE ENTIRE STATE AND TEMPS SHOULD RANGE FROM THE M30S OVR THE ALLEGHENY MTNS...TO THE M40S ACROSS THE SUSQ VALLEY. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/... CHRISTMAS DAY WILL BRING A TRANSITION INTO A PRETTY TYPICAL POST FRONTAL COOL SEASON PATTERN...WITH CLOUDS AND BLUSTERY GUSTY WESTERLY WINDS. HIGHER ELEVATIONS WILL LIKELY SEE GUSTS AS HIGH AS 40-45 MPH...WHILE BUKFIT DATA IMPLIES TOP WGUSTS IN THE 35-40MPH RANGE FOR THE REST OF US. THE AIR MASS WILL BE FAR FROM COLD FOR LATE DECEMBER STANDARDS...BUT COLD ENOUGH TO SUPPORT SCT OROGRAPHIC SNOW SHOWERS OVR THE ALLEGHENY PLATEAU...WITH THE CENTRAL RIDGE-VALLEY REGION SEEING LITTLE MORE THAN A PASSING LIGHT RAIN OR SNOW SHOWER. WITH SFC TEMPS EXPECTED TO BE ABV FREEZING EVERYWHERE AND SNOW SHOWERS LIGHT...EXPECT NO ACCUMULATION EXCEPT PERHAPS A DUSTING OVR THE HIGHEST RIDGETOPS. ENS MEAN 925/850 TEMPS SUPPORT HIGH TEMPS CHRISTMAS DAY FROM THE M30S OVR THE ALLEGHENY MTNS...TO NR 50F ACROSS THE LOWER SUSQ VALLEY. && .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/... POTENT LONGWAVE UPPER TROF EXITING THE EAST COAST AT THE START OF THE PERIOD WILL BE REPLACED BY UPPER RIDGING INTO THE WEEKEND. AS LONGWAVE UPPER TROFFING IS FORECAST TO DEVELOP OVER THE WRN US STARTING EARLY IN THE PD AND NRN STREAM ENERGY RETREATS INTO EASTERN CANADA...MDT TO STRONG SWRLY FLOW ALOFT IS THEN FORECAST TO DOMINATE THE EASTERN CONUS FROM LATE IN THE WEEKEND THROUGH THE REMAINDER OF THE YEAR. MEDIUM RANGE GUIDANCE IS FAIRLY CONSISTENT ESPECIALLY EARLY IN THE PERIOD...BUT THEN SOME DIFFERENCES ARISE IN 500MB FLOW PATTERN AFTER MONDAY AS THE ECMWF MOVES ENERGY EAST FASTER...WHILE THE GFS CLOSES OFF AN UPPER LOW OVER THE DESERT SW. A NORTHERN STREAM WAVE IS FORECAST TO SUPPORT A COLD FRONT MOVING EAST ACROSS THE STATE LATE IN THE WEEKEND...POSSIBLY STALLING NEAR THE MASON DIXON LINE INTO MONDAY AS IT ENCOUNTERS RESISTANCE FROM THE BUILDING UPPER FLOW. THIS FRONT LOOKS TO BE THE MAIN FOCUS FOR PCPN IN THE LONG TERM PERIOD. WITH SNOW TO THE NORTH AND WEST...AND A MIX TO RAIN ACROSS THE SOUTH. WITH RIDGING OR SWRLY FLOW ALOFT MUCH OF THE PERIOD WILL FEATURE ABOVE NORMAL TEMPS...WITH A COOL DOWN TOWARD NORMAL BY NEW YEARS EVE. && .AVIATION /01Z THURSDAY THROUGH MONDAY/... THE MAIN CONCERNS REMAIN LIFR TO MVFR CONDITIONS AND LLWS THIS EVENING. HOWEVER...WATCHING LINE OF STORMS WEST OF PA. SINCE WE ARE AT LEAST 10 DEGREES COOLER AND DEWPOINTS LOWER...THINK ANY REAL STRONG STORMS WILL WEAKEN AS THEY MOVE TOWARD CENTRAL PA. WILL CONTINUE TO MONITOR. 21Z TAFS SENT. EARLIER DISCUSSION BELOW. WIDESPREAD MVFR/IFR WITH RAIN AND AREAS OF FOG WILL CONTINUE INTO THE EVENING AS A STORM SYSTEM MOVES INTO THE EASTERN GREAT LAKES THIS EVENING. THE ASSOCIATED TRAILING COLD FRONT WILL PUSH THROUGH CENTRAL PENNSYLVANIA TONIGHT. ISOLATED EMBEDDED THUNDERSTORMS CANNOT BE RULED OUT ALONG THE FRONT. STRONG AND GUSTY WEST WINDS WILL DEVELOP BEHIND THE FRONT TONIGHT AND THURSDAY. INCLUDED LLWS FOR ALL TAF SITES AS WINDS ALOFT BEGIN TO INCREASE AHEAD OF THE APPROACHING FRONTAL SYSTEM WHILE SFC WINDS REMAIN RELATIVELY LIGHT OUT OF THE SE. WESTERN HIGH TERRAIN TERMINALS WILL HOLD ONTO REDUCED CONDITIONS THROUGH MUCH OF CHRISTMAS DAY AFTER WINDS SHIFT TO THE WEST BEHIND THE COLD FRONT...WHILE CENTRAL AND EASTERN TERMINALS WILL SEE CEILINGS IMPROVE TO THE 3000-5000` RANGE BY LATE TONIGHT OR FAIRLY EARLY CHRISTMAS MORNING. OUTLOOK... FRI...FAIR AND MOSTLY VFR. SAT...VFR. SUN...MVFR TO IFR WITH SCATTERED RAIN SHOWERS. MON...NO SIG WX. && .CTP WATCHES/WARNINGS/ADVISORIES... WIND ADVISORY UNTIL NOON EST THURSDAY FOR PAZ004>006-010>012- 017-018-024-033. && $$ SYNOPSIS...LA CORTE NEAR TERM...FITZGERALD SHORT TERM...FITZGERALD/LA CORTE LONG TERM...LAMBERT/GARTNER AVIATION...MARTIN

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