Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 301939 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 339 PM EDT MON MAR 30 2015 .SYNOPSIS... A POTENT BUT RELATIVELY FAST MOVING AREA OF LOW PRESSURE WILL MOVE SOUTHEAST FROM THE WESTERN GREAT LAKES TONIGHT AND RIDE ALONG THE MASON-DIXON LINE TUESDAY...BRINGING HIGHLY ELEVATION DEPENDENT SNOW ACCUMULATION OF A FEW TO SEVERAL INCHES ACROSS THE NORTHERN HALF TO TWO THIRDS OF PENNSYLVANIA. MIXED PRECIPITATION OR RAIN WILL FALL ACROSS THE SOUTHERN TIER OF PENNSYLVANIA. A SHARP MODERATION IN TEMPERATURES WILL OCCUR THURSDAY BEFORE A NEW COLD FRONT APPROACHES FOR FRIDAY WITH RAIN SHOWERS...POSSIBLY CHANGING TO A PERIOD OF SNOW AT NIGHT ACROSS MUCH OF CENTRAL AND NORTHERN PENN. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... GUSTY WNW WINDS WITH MSTLY CLOUDY TO CLOUDY SKIES AND A FEW BANDS OF BRIEF RAIN SHOWERS...AND MTN SNOW SHOWERS WILL PREVAIL THROUGH SUNSET. BRIEF CLEARING WILL OCCUR EARLY TONIGHT WITH WINDS TAILING OFF TO LIGHT AND VARIABLE IN MANY LOCATIONS AFTER MIDNIGHT. THIS WILL ALLOW MIN TEMPS TO SETTLE INTO THE MID 20S TO LOWER 30S. THE STAGE WILL BE SET FOR YET ANOTHER EARLY SPRING /WINTRY/ WEATHER EVENT FOR MUCH OF CENTRAL AND NORTHERN PENN BEGINNING AROUND OR SHORTLY BEFORE DAYBREAK TUESDAY ACROSS THE WESTERN MTNS...THEN SPREADING ACROSS THE REMAINDER OF THE REGION DURING THE MID TO LATE MORNING HOURS. MORE TO FOLLOW IN THE SHORT TERM SECTION BELOW. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... MODELS ARE IN GOOD AGREEMENT ON THE TRACK OF A POTENT CLIPPER ALONG THE MASON-DIXON LINE DURING THE DAY TUESDAY. THREE OR FOUR FACTORS GREATLY COMPLICATE THE FORECAST FOR SNOWFALL AMOUNT ACROSS THE REGION TUESDAY. THE FIRST BEING THE EXACT TRACK AND QPF...SECOND IS THE TIMING OF THE HEAVIEST SNOWFALL RATES DURING THE MORNING /A FEW HOURS FASTER MEAN MORE SNOW/...AND THIRD BEING A LARGE DEGREE ELEVATION DEPENDENCY. IN ANY CASE...A SEVERAL HOUR PERIOD OF MODERATE TO STG UVVEL ASSOCIATED WITH THE LEFT EXIT REGION OF A 100 KT UPPER JET WILL BRING A MODERATE TO BRIEFLY HEAVY SNOW TUESDAY MORNING...GRADUALLY TAPERING TO AREAS OF LIGHTER SNOW/SNOW SHOWERS FOR THE MID TO LATE AFTERNOON. LIKELY SNOWFALL WILL VARY FROM 1-3 INCHES IN THE VALLEYS...AND UP TO 4 OR 5 INCHES OF HEAVY WET SNOW ACROSS THE HIGHER TERRAIN NEAR AND TO THE NORTH OF THE RT 322 CORRIDOR. THERE MAY BE LITTLE OR NO SNOW SOUTH OF THE TURNPIKE AND WEST OF INTERSTATE 81...ALONG AND JUST SOUTH OF THE LOW TRACK. AFTER COORDINATION WITH SURROUNDING OFFICES...WE WANTED TO WAIT FOR AT LEAST ONE MORE RUN TO CONFIRM THE TIMING TRACK AND QPF AMOUNTS BEFORE COORDINATING AN ADVISORY FOR A BORDERLINE AND HIGHLY ELEVATION INFLUENCED EVENT. MULTI MODEL TEMPS FOR TUESDAY/S MAXES ARE IN THE MID 30S ACROSS THE NRN MTNS...AND UPPER 30S TO MID 40S IN CENTRAL PENN...WITH HIGHS AROUND 50F IN THE SOUTH. UNLESS IT SNOWS FAIRLY HARD...MOST ACCUMS AFTER 15Z WILL LIKELY BE ON GRASSY SURFACES. OVER CENTRAL AREAS WHERE A RAIN-SNOW MIX IS LIKELY FOR A TIME...IT SHOULD BE TOO WARM TO STICK. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... HIGH PRESSURE SHOULD BRING DRY WEATHER FOR MIDWEEK BEFORE THE PATTERN TURNS INCREASINGLY UNSETTLED DURING THE LAST PART OF THE WEEK. THE LATEST NAEFSBC HAS NOT CHANGED THE OVERALL THINKING THAT A WARMING TREND WILL DEVELOP AHEAD OF THE LATE WEEK COLD FRONT. THE DETAILS OF THE FRONT AT THIS RANGE REMAIN FUZZY AS THE OPERATIONAL ECMWF AND GFS HAVE TIMING AND INTENSITY ISSUES. THE GFS DROPS THE FRONT INTO PA THURS NIGHT WHILE THE ECMWF STILL HAS IT THROUGH THE LOWER GR LAKES. THE DIFFERENCES BETWEEN THE TWO OPERATIONAL MODELS MEAN FRIDAY COULD EITHER BE MAINLY DRY WITH THE FRONT SETTLING SOUTH...GFS...OR WET AS THE FRONT ENTERS THE REGION...ECMWF. FROM THERE IT GETS A LITTLE MORE COMPLICATED AGAIN WITH A TRAILING WAVE OR WAVES MADE TO SURGE OUT OF THE TN VALLEY INTO THE REGION FRIDAY NIGHT INTO SATURDAY. THE EC ENSEMBLE HINTS AT A WAVY FRONT WITH PERHAPS A COUPLE OF LOWS RIPPLING ALONG IT EVENTUALLY MOVING THROUGH CENTRAL PA...WHILE THE GFS/GEFS ARE MORE IN LINE WITH A SINGLE MORE COHERENT LOW TAKING A MORE SOUTHERN TRACK. BECAUSE OF THE UNCERTAINTY WITH THESE SCENARIOS...I KEPT POPS IN THE CHANCE RANGE FOR THURS INTO FRIDAY NIGHT BEFORE BEGINNING TO DRY THINGS OUT FOR SATURDAY. IT SEEMS LIKELY THERE WILL BE SOMEWHAT OF A COOL DOWN OVER THE WEEKEND AFTER THE FRONT PASSES AND WE SEE THE UPPER LOW OVER HUDSON`S BAY SINK SOUTH ONCE AGAIN. WHILE WE WILL COOL DOWN...THE LARGER SCALE FLOW OVER WESTERN NOAM IS EXPECTED TO HAVE MORE OF A PACIFIC ORIGIN SO TEMPS SHOULD NOT CONTINUE THE TREND OF BEING WELL BELOW NORMAL AS WE HAVE SEEN FOR MUCH OF THE LAST 2 MONTHS. && .AVIATION /19Z MONDAY THROUGH SATURDAY/... GUSTY WNW WINDS AVERAGE 10-15 KTS FOR THE NEXT SEVERAL HOURS...WITH GUSTS OF 25 TO 30 KTS AT TIMES WILL BE THE RULE IN THE WAKE OF THE COLD FRONT THROUGH THE REST OF THE DAYLIGHT HOURS. VFR WILL CONTINUE ACROSS ALL CENTRAL PA AND SUSQ VALLEY TAF SITES...WHILE MVFR CIGS WILL BE FOUND FOR THE REST OF TODAY ACROSS THE HIGHER ELEVATION AIRFIELDS OF KJST...KFIG AND KBFD. A FAST MOVING CLIPPER TYPE LOW WILL SPREAD A SHIELD OF STEADY LIGHT TO MDT SNOW ACROSS THE NORTHERN THIRD TO HALF OF PENN VERY LATE TONIGHT AND TUESDAY MORNING WITH CONDITIONS DROPPING TO IFR/LIFR FROM BFD TO POINTS EAST TWD KIPT AND KAVP. IFR IN MIXED PRECIP OR SNOW APPEARS LIKELY FOR THE CENTRAL THIRD OF THE STATE TUESDAY MORNING/EARLY AFTERNOON...WHILE A FEW PERIODS OF LIGHTER RAIN/SNOW SHOWERS WILL OCCUR ACROSS THE SOUTHERN TIER COUNTIES OF PENNSYLVANIA. SOME BRIEF AND LIGHTER RAIN AND SNOW SHOWERS FOR LATE TUESDAY AFTERNOON INTO EARLY WEDNESDAY...IN THE WAKE OF THE LOW PRESSURE AREA. LOOKING COLD BUT DRY ON WED. A SHARP...BUT BRIEF WARMING FOR THURSDAY...WITH A GUSTY SW WIND OF 20-30KTS. OUTLOOK... TUE...CHANCE OF LIGHT SNOW/RAIN...MAINLY ACROSS THE NW HALF WITH MVFR REDUCTIONS. WED-THU MORNING...MAINLY VFR...AS HIGH PRESSURE BUILDS ACROSS THE AREA. THU PM-FRI...LOWERING CONDITIONS TO MVFR WITH SCATTERED RAIN SHOWERS...AS A COLD FRONT MOVES EASTWARD. && .CTP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...LAMBERT NEAR TERM...LAMBERT SHORT TERM...LAMBERT LONG TERM...LA CORTE AVIATION...LAMBERT

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