Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 291207 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 707 AM EST THU JAN 29 2015 .SYNOPSIS... HIGH PRESSURE WILL DRIFT OFF THE ATLANTIC SEABOARD TODAY...ALLOWING CLOUDS TO THICKEN UP AHEAD OF AN ALBERTA CLIPPER. THIS FAST MOVING AREA OF LOW PRESSURE WILL CROSS THE AREA THIS AFTERNOON AND TONIGHT...PRODUCING A FEW PERIODS OF SNOW...ALONG WITH THE CHANCE FOR SOME LIGHT MIXED PRECIPITATION ACROSS SOUTHERN PENNSYLVANIA. HIGH PRESSURE WILL RETURN FOR LATE FRIDAY INTO SATURDAY. A NEW STORM MAY BRING A ROUND OF WINTRY WEATHER FOR LATER SUNDAY INTO MONDAY...BEFORE ANOTHER SURGE OF COLD AIR WORKS INTO THE AREA EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... MID AND HIGH CLOUD COVER THICKENING UP ACROSS THE WESTERN HALF OF PENN EARLY THIS MORNING...WHILE SKIES ARE STILL MCLEAR ACROSS THE SUSQ VALLEY AND POINTS EAST. THE EARLIER CLEAR SKIES...LIGHT WIND AND FRESH SNOW COVER ALLOWED TEMPS TO BRIEFLY DIP AS LOW AS -4 TO -7F ACROSS PORTIONS OF ELK...MCKEAN AND POTTER COUNTIES. TEMPS THERE HAVE INCREASED A FEW DEG F OVER THE PAST 2 HOURS AS THE THICKER CLOUDS OVERSPREAD THE AREA. MESO OBS SHOW TEMPS NEARING MINS /IN THE SINGLE DIGITS TO LOW TEENS/ ACROSS THE SUSQ VALLEY ATTM. A FEW REPORTS BELOW ZERO WERE NOTED AT KSEG /-1F/ AND AT MANSFIELD IN TIOGA COUNTY /-8F/. THE LOWERING/THICKENING...MID CLOUD SHIELD WILL REACH A KELZ TO KUNV AND KMRB LINE AROUND 12Z...BEFORE PROGRESSING EAST ACROSS THE SUSQ VALLEY DURING THE LATE MORNING HOURS. ASIDE FROM A FEW FLURRIES ACROSS THE NW MTNS AROUND OR SHORTLY AFTER DAYBREAK...CONDITIONS WILL BE BONE DRY AND VERY COLD THROUGH 13Z. CLOUDS WILL THICKEN QUICKLY TODAY WITH WARM ADVECTION PRECIP OVERSPREADING THE AREA DURING THE AFTERNOON. A STRONG SHOT OF WAA ALOFT AND MODERATELY STG UPPER LEVEL DIVERGENCE ASSOCIATED WITH THE RIGHT ENTRANCE REGION OF AN UPPER LVL JET MAX ACROSS SRN ONTARIO WILL LEAD TO PERIODS OF LIGHT /TO BRIEFLY MDT SNOW/ FOCUSED ACROSS THE NW HALF OF THE STATE THIS AFTERNOON INTO TONIGHT. 00-06Z OPERATIONAL MODELS/GEFS...ALONG WITH THE 21-03Z SREF ALL AGREE IN SHOVING A WEDGE OF WARMER AIR ALOFT INTO THE AREA THIS MORNING...BUT FORECAST SOUNDINGS SHOW THE INITIALLY VERY DRY AND SLIGHTLY ABOVE FREEZING COLUMN /ACROSS THE SOUTHERN HALF OF PENN/ QUICKLY COOLING TO A FEW DEG C BELOW ZERO ONCE PRECIP STARTS...SO THE THREAT FOR SIG ICING WILL BE MINIMAL AT BEST. MODEL CONSENSUS REMAINS UNCHANGED TO A LARGE DEGREE WITH RESPECT TO THE QPF FROM THE CLIPPER SYSTEM MOVING BY JUST TO OUR NORTH ACROSS LAKES ERIE AND ONTARIO LATE TODAY AND TONIGHT. A GENERAL 2-4 INCH SNOWFALL IS LIKELY OVER THE ALLEGHENIES OF WRN PENN WHERE A WINTER WEATHER ADVISORY IS IN EFFECT FROM LATE THIS MORNING THROUGH 12Z FRIDAY. THE CENTRAL RIDGE AND VALLEY OF THE STATE WILL 1-2 INCHES BY MIDNIGHT TONIGHT...WHILE COUNTIES THROUGHOUT THE LOWER SUSQ VALLEY RECEIVE GENERALLY LESS THAN 0NE INCH. A BIT OF SLEET AND EVEN PATCHY ICE FROM LIGHT FREEZING RAIN IS POSSIBLE ACROSS SOUTHERN PENN LATE TODAY AND THIS EVENING AS THE RATHER SHALLOW WEDGE OF WARMER AIR ALOFT DRIFTS EAST. HIGHS THIS AFTERNOON WILL REACH THE UPPER 20S TO AROUND FREEZING IN THE INCREASING/BRISK SW FLOW AHEAD OF THE CLIPPER/ARCTIC FRONT. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/... THE BRUNT OF THE CURRENT STORM SYSTEM WILL OCCUR LATE THIS AFTERNOON AND EARLY TONIGHT...WITH SOME BRIEF PERIODS OF MDT SNOW LIKELY AS ONE OR MORE N/S BANDS OF ENHANCED 850-700 MB UVVEL CROSSES THE REGION. 03Z SREF INDICATES THAT AN AXIS OF ANOMALOUS /2-3 SIGMA/ 850MB MOISTURE FLUX AND SIMILARLY ANOMALOUS /50 KT/ SWRLY LLJ WILL BE GRADUALLY WEAKENING AS IT CROSSES PENN BETWEEN 21Z AND 06Z FRI. SFC COLD FRONT EXTENDING SOUTH FROM THE LOW...PUSHES ACROSS OUR WESTERN ZONES LATE THIS EVENING...THEN CLEARS THE SUSQ VALLEY BETWEEN 07-09Z FRIDAY. SNOW WILL TAPER TO SNOW SHOWERS BY LATE TONIGHT...MAINLY IN THE ISOLATED FORM ACROSS THE CENTRAL AND SOUTHERN VALLEYS. LOW TEMPS TONIGHT WILL RANGE FROM THE MID TO UPPER TEENS ACRS THE WRN MTNS...TO THE MID AND UPPER 20S ACROSS THE SUSQ VALLEY. A SLIGHTLY EARLIER TIMING OF THE CFROPA WILL KNOCK THESE VALUES DOWN BY A FEW DEG F. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... PERIODS OF GENERALLY LIGHTER SNOW WILL LINGER INTO EARLY FRIDAY...AS THE MAIN COLD FRONT DROPS SE. A TIGHT LLVL PRESSURE GRADIENT IN THE WAKE OF THE COLD FRONT WILL BRING GUSTY NORTHWEST WINDS AND SLOWLY FALLING TEMPS ACROSS THE REGION DURING THE DAYLIGHT HOURS FRIDAY. WIND GUSTS WILL BE IN THE MID TO UPPER 20 KT RANGE FOR MOST AREAS CREATING A WIND CHILL IN THE SINGLE DIGITS TO LOW TEENS IN THE SUSQ VALLEY....AND 5 BELOW TO 15 BELOW ACROSS THE NRN AND WRN MTNS. FRIDAY NIGHT WILL BE BITTERLY COLD...AS SKIES CLEAR AND WINDS DIE DOWN. LOW TEMPS WILL VARY FROM THE SINGLE DIGITS BELOW ZERO ACROSS THE NORTH...TO SINGLE DIGITS ABOVE ZERO IN THE SOUTH. A BRIGHT DAY ON SAT...BUT NOT REAL WARM. STILL HAVE CHC POPS ON SUNDAY. A LOT OF SPREAD IN THE MODEL OUTPUT THE LAST FEW DAYS. 12Z MODELS BACKING OFF SOME NOW. PATTERN SUPPORTS LOW PRESSURE SYSTEMS THAT ARE FAST MOVING AND WEAK. WOULD STILL EXPECT SOME LIGHT SNOW INTO MONDAY MORNING. A COLD NIGHT MONDAY NIGHT...AS THE NEXT HIGH BUILDS INTO THE AREA. SOME HINTS AT ANOTHER FAST MOVING LOW FOR MID WEEK...FOR NOW WENT WITH CHC POPS. MINOR CHANGES TO THE PACKAGE MADE. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... VFR WILL CONTINUE THROUGH THE FIRST HALF OF THE DAY. CLOUDS WILL INCREASE AS CONDITIONS DETERIORATE AS THE SNOW WILL START AROUND MID DAY OVER WESTERN TERMINALS...SPREADING RAPIDLY EAST THROUGH MID AFTERNOON. THERE WILL BE SOME MIXED PRECIPITATION THROUGH THE SOUTHERN HALF OF CENTRAL PA. EXPECT IFR CONDITIONS AT MOST TERMINALS BEGINNING WEST TO EAST BETWEEN 19Z TO 00Z AND DECREASING RAPIDLY FROM MVFR TO IFR. REDUCED CONDITIONS SHOULD IMPROVE OVERNIGHT AROUND 06Z FRIDAY...THOUGH MVFR COULD CONTINUE UNTIL 12Z FRIDAY...ESPECIALLY AT BFD AND JST. OUTLOOK... FRI...CONDITIONS IMPROVING DURING THE DAY...BUT REMAINING MVFR OVER THE HIGHER ELEVATION TERMINALS OF THE WEST AND NORTH. SAT...VFR. SUN...RESTRICTIONS DEVELOPING WITH SNOW OVERSPREADING FROM THE WEST. MON...REDUCED CONDS EARLY IN SNOW. IMPROVING FROM WEST TO EAST AFTERNOON ONWARD. && .CTP WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY FROM 11 AM THIS MORNING TO 7 AM EST FRIDAY FOR PAZ004>006-010-011-017-024-033. && $$ SYNOPSIS...LAMBERT NEAR TERM...LAMBERT SHORT TERM...LAMBERT LONG TERM...LAMBERT/MARTIN AVIATION...CERU/GARTNER

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