Area Forecast Discussion
Issued by NWS State College, PA

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614 FXUS61 KCTP 071740 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 1240 PM EST SUN FEB 7 2016 .SYNOPSIS... HIGH PRESSURE WILL PROVIDE ONE MORE FAIR AND RELATIVELY MILD DAY TODAY. A 36 TO 48 HOUR PERIOD OF SNOW WILL LIKELY RESULT IN A A WIDESPREAD LIGHT TO MODERATE SNOWFALL FOR MUCH OF CENTRAL PA MONDAY NIGHT THROUGH TUESDAY. LAKE EFFECT AND UPSLOPE SNOW SHOWERS WILL CONTINUE THROUGH THE END OF THE WEEK WITH ADDITIONAL ACCUMULATION LIKELY IN THE FAVORED NORTHWEST SNOWBELT AND HIGHER TERRAIN ALONG THE ALLEGHENIES AND LAURELS. A MUCH COLDER WEATHER PATTERN IS EXPECTED BY LATER IN THE WEEK WITH A BLAST OF ARCTIC AIR FOR VALENTINES WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... ABUNDANT SUNSHINE...GENERALLY LIGHT WIND...AND TEMPS BETWEEN 6 AND 8 DEG F ABOVE NORMAL WILL BE THE RULE FOR THIS AFTERNOON...AS THE FORECAST AREA STAYS SANDWICHED BETWEEN CLOUDS TO THE NORTHWEST AND SOUTH /ASSOCIATED WITH RAPIDLY DEEPENING LOW PRESSURE OFF THE S CAROLINA COAST/. THIS WILL BE THE LAST FAIR WEATHER DAY FOR SOME TIME AS A A SLOWLY DEVELOPING UPPER LOW DROPS INTO THE EASTERN US AND BRINGS A PROLONGED PERIOD OF SNOWY AND EVENTUALLY MUCH COLDER WEATHER TO THE REGION FOR THE NEW WORK WEEK. FOR THE OVERNIGHT HOURS TONIGHT...WE/LL BEGIN TO SEE A SLOW INCREASE IN CLOUDINESS. IT WILL STILL BE RELATIVELY MILD WITH LOWS IN THE 20S IN MOST AREAS. && .SHORT TERM /MONDAY/... CONSIDERABLE UNCERTAINTY EXISTS WITH THE ONSET OF WHAT AT LEAST INITIALLY LOOKS LIKE SOME LIGHT PRECIPITATION AS THE UPPER LOW DIGS THROUGH THE UPPER MIDWEST ON A TRACK TOWARD THE OHIO VALLEY AND EVENTUALLY NERN US. THE SREF WAS SLOWEST IN BRINGING IN THE PRECIP MONDAY...WHICH COULD ACTUALLY BE A LIGHT MIX OF RAIN AND SNOW GIVEN THE EXPECTED HIGHS IN THE 30S TO LOWER 40S. I USED OUR BLENDED MODEL POPS WHICH ARE A BIT HIGHER THAN THE DRY SREF FOR THE AFTERNOON...WITH THE BEST CHANCE OF SOME LIGHT SNOW...OR A LIGHT RAIN/SNOW MIXTURE BEING OVER WESTERN AREAS...WITH LESSER CHANCES OVER EASTERN ZONES. IN GENERAL I CUT THE ALREADY LIGHT WPC-GUIDANCE SNOWFALL AMOUNTS BY ABOUT HALF GIVEN THAT SKIN TEMPS WILL BE RELATIVELY WARM AND WITH PRECIP RATES WHICH ARE EXPECTED TO BE ON THE LIGHT SIDE. THAT USUALLY MAKES IT HARD FOR SNOW TO STICK TO MUCH MORE THAN GRASSY SURFACES...EVEN IN AREAS WHERE IT DOES NOT MIX WITH RAIN. IT IS FAIRLY CERTAIN CENTRAL PA WILL EXPERIENCE A PROLONGED PERIOD OF LIGHT...POSSIBLY MODERATE PRECIP FOR THE EARLY PART OF THE EXTENDED PERIOD OF THE FORECAST. CONFIDENCE REMAINS LOW HOWEVER AS TO WHICH PERIOD WILL SEE THE BEST CHANCE OF SNOW AMOUNTS THAT MIGHT WARRANT HEADLINES. THE GEFS SHOWS AT BEST A 30% PROB OF HALF INCH QPF IN THE PERIOD BETWEEN 06Z AND 18Z TUESDAY. THE ECENS IS SIMILARLY LOW KEY REGARDING THE BEST PERIOD FOR ACCUM SNOW...TAKING 6 DAYS TO REACH 6 INCH TOTALS...AND THOSE ARE IN THE USUAL LAKE EFFECT AND LAUREL HIGHLAND UPSLOPE AREAS...NOT NECESSARILY ASSOCIATED WITH A SINGLE COHERENT SURFACE CYCLONE. THE 00Z GFS COMES THE CLOSEST TO ZEROING IN ON A THREAT AREA...SHOWING THE SERN 1/3 OF THE CWA UNDER THE GUN AFTER 06Z TUESDAY THROUGH 18Z...WITH AN ELONGATED SURFACE LOW HELPING SUPPORT AN AREA OF FRONTOGENETIC FORCING INTO THE LOWER SUSQ VALLEY. IT SUPPORTS THIS IDEA WITH ABOUT 12-18 HOURS OF FAIRLY STRONG EASTERLY LOW LEVEL FLOW WHICH THE GEFS IS NOT NEARLY AS ROBUST IN PORTRAYING. THE ECENS FOR THE SAME TIME FRAME HAS A MUCH LESS VIRILE DEPICTION OF THIS WRAP-BACK INTO THE SERN AREAS. THE NAM/SREF ARE SIMILARLY LESS IMPRESSIVE WITH THE POTENTIAL FOR SIG SNOW OVER SERN ZONES. IT ALL POINTS TO CONTINUING LOW CONFIDENCE IN PICKING OUT THE BEST PERIODS FOR THE MOST QPF...BUT A RELATIVELY HIGH CONFIDENCE THAT ONCE PRECIP BEGINS...IT WILL CONTINUE FOR SEVERAL FORECAST PERIODS. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... ANOMALOUS WESTERN US RIDGE/EASTERN US TROUGH PATTERN WILL BE IN PLACE THROUGH MID WEEK. THE GLOBAL ENSEMBLE MEANS GENERALLY KEEP THIS PATTERN CONFIGURATION INTACT INTO THE WEEKEND BUT AT A SLIGHTLY DECREASING AMPLITUDE..ESPECIALLY THE WESTERN US RIDGE. AS THE BROAD UPPER LEVEL CIRCULATION DEPARTS OVER THE NORTHEAST TOWARD THE END OF THE WEEK...THE GLOBAL MODELS SHOW IT BEING REPLACED BY A POLAR VORTEX DROPPING SOUTH FROM THE ARCTIC. COLD AIR WILL BEGIN SPILLING SOUTHWARD FROM CANADA LATER IN THE WEEK REINFORCED INITIALLY BY A SECONDARY FRONT ON THURSDAY...FOLLOWED BY A SIGNIFICANT ARCTIC AIR INTRUSION FOR VALENTINE`S WEEKEND. RESIDUAL SNOWS ASSOCIATED WITH THE UPPER TROUGH ON WED SHOULD TRANSITION TOWARD LAKE EFFECT/UPSLOPE FOR SEVERAL DAYS THU-SAT WITH ADDITIONAL ACCUMULATION LKLY OVER THE FAVORED AREAS DOWNWIND OF LAKE ERIE AND IN THE HIGHER TERRAIN OF THE ALLEGHENIES/LAURELS. CONFIDENCE IS HIGH IN THE FCST COLD PATTERN WHICH SHOULD PEAK OVER THE WEEKEND. MAX/MIN TEMPERATURE DEPARTURES OF 20 DEGREES BELOW CLIMO ARE PROBABLE SAT-SUN. WIDESPREAD SUB ZERO WIND CHILLS APPEAR LIKELY SATURDAY NIGHT INTO EARLY SUNDAY...WITH PROJECTED MINIMUM WC VALUES BETWEEN -10 TO -25 DEGREES BELOW ZERO. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... HIGH PRESSURE OVER THE AREA WILL RESULT IN JUST A FEW HIGH CLDS LATE TODAY...THOUGH THE SOUTHEAST TAF SITES /KLNS AND KMDT/ WILL SEE A THICKER SHIELD OF CIRROSTRATUS OCCASIONALY DIMMING THE SUN. OVERALL...A NICE FLYING DAY FOR EARLY FEBRUARY WITH GENERALLY LIGHT AND VARIABLE WIND. A COMPLEX WEATHER PATTERN MAY RESULT IN SOME SNOW AND COLDER TEMPERATURES AFTER TODAY AS A DEEP UPPER TROUGH BECOMES CARVER OUT OVER THE EASTERN U.S. OUTLOOK... MON...PM LGT SNOW POSSIBLE...ESP W MTNS. MON NIGHT AND TUE...LGT SNOW LIKELY...ESP CENTRAL AND WRN MTNS. WED...IFR/MVFR IN SHSN WRN AIRSPACE. MVFR-VFR CIGS CENTRAL/EAST. SFC WIND GUSTS 20+KT FROM 270-300. THU...MVFR IN -SHSN POSSIBLE W MTNS. && .CTP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...STEINBUGL/LA CORTE NEAR TERM...LAMBERT/LA CORTE SHORT TERM...LA CORTE LONG TERM...STEINBUGL AVIATION...LAMBERT/MARTIN

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