Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 031643 AFDCTP Area Forecast Discussion National Weather Service State College PA 1143 AM EST Sat Dec 3 2016 .SYNOPSIS... High pressure will build in later today but slide quickly off to the east on Sunday. A weak frontal boundary passing through Sunday night will cause light snow in the north and rain or snow in the south. A storm with mainly rain may affect the area during mid- week, some mixed precipitation may occur at the beginning of that storm. && .NEAR TERM /UNTIL 7 PM THIS EVENING/... 1030 AM update... Widespread stratocu will persist through the afternoon hours as slowly decreasing, deep cyclonic flow combines with broad large scale lift beneath the right entrance region of an anomalously strong 170-180kt upper jet lifting north across the state attm. Well-aligned flow on an approx 310 deg axis in the lowest several kft agl will maintain several narrow bands of light snow/rain showers across the NE half of the CWA thanks to a tap of llvl moisture with a fetch over a fairly long axis of lake erie. Pops in the chc to low likely category were still limited to mainly the higher terrain to the north of I-80, though some very light rain and snow showers will reach about 20-30 miles south at times with QPF of 0.01 or 0.02 possible in a few locations. a light additional coating of snow is possible at elevations over 2000 ft MSL, otherwise, sfc temps are too warm and precip rates generally to light. Current temps are on track to reach highs in the mid to upper 30s across the nrn and western mtns and 40s throughout the central and SE zones. The brisk northwest wind will continue, before slowly abating late today/this evening as a ridge of high pressure builds in from the Ohio Valley. && .SHORT TERM /7 PM THIS EVENING THROUGH MONDAY/... Flow relaxes tonight as sfc ridge slides overhead for Sunday morning. Some decrease in cloud coverage is expected overnight (mainly over the SE half of the CWA), but it turns right around during the day on Sunday. A solid bkn-ovc mvfr to IFR stratocu deck may linger for much of the night across the Alleghenies of northern and Western PA. High/mid/low cloud progression will darken things again wherever breaks/clearing does occur. The E/SE will stand the best chance for complete clearing. Temps will be cooler tonight without so much wind to keep us well-mixed. Biggest challenge in this cycle is what kind/how much precip falls Sunday night from the passage of a weak front. All the models and most of the GEFS members crank out 0.05-0.20 inches of QPF for Sun night as the feature is carried steadily through by mainly zonal flow. Most of the precip should be snow, but it is not likely to stick in many places SE of the Allegheny Front. Just the highest hill tops of the SE may get a dusting. For a few runs, a weakness exists in the QPF right through Central PA from W-E. This seems to be a disconnect between the moisture and the left-exit region of a 150kt jetlet which passes right over the state. Temps are marginal for accums, and QPF is light. Have drawn 1-2 inches across the nrn tier of counties. It is a nighttime event, and temps in the nrn tier are much more likely to be sub-freezing all night. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... There is decent agreement in bringing the SW US upper low up through the Ohio Valley on Tuesday as a shearing out shortwave and diffuse surface low. Unless cold air damming traps enough chilly air in the low levels to make for some freezing rain, the precip type with this midwest system looks to be mainly rain. Have raised POPs into the categorical range as it seems unlikely that we will get missed. The end of the week brings some model disagreement with the GFS/GEFS being faster than the ECMWF with the next large upper trof and frontal system. Either way, precip looks like a good bet around the Thu/fri period as all solutions eventually bring this trough through. So predictability is increasing, but timing issues remain. Best bet for precip at this point is mainly rain over the SE as decent push of warm air lifts ahead of the system, with a rain/snow mix further north where warm air will not infiltrate as much. Behind the trough, looks like a chilly weekend in store with a potential sharp dropoff in temps. && .AVIATION /16Z SATURDAY THROUGH WEDNESDAY/... 16Z satellite loop shows widespread, mainly non-precipitating shallow/warm stratocu blanketing all central PA taf sites. CIGs ranging from IFR at KJST to low MVFR at KBFD, with VFR between 4-5kft at the lower elevation Central PA airfields, including KIPT/KMDT/KMDT. These conditions will likely be very stable through at least 00Z Sunday, if not through much of tonight as the flow within the lowest 3-4 kft agl stays quite well-aligned from about 290 deg with a feed of llvl moisture off Lake Erie. This moist WNW flow forced to ascend the Appalachians will create borderline IFR/low MVFR CIGs and occasional snow showers. Downsloping flow will result in progressively better conditions further east, with MVFR cigs likely at KUNV/KAOO and VFR conditions at KIPT/KMDT/KLNS. High pressure approaching from the west will cause snow showers to diminish across the NW Mtns later today. However, model soundings still indicate persistent MVFR CIGs at KBFD/KJST through this evening. WNW winds should continue to gust between 15-22kts through mid afternoon, followed by gradually diminishing winds this evening as high pressure builds in. Outlook... Sun...Light snow/reduced vis possible at night, mainly NW Mtns. Mon...No sig wx expected. Tue...Mixed precip/low CIGs possible, especially late. Wed...Lingering low CIGs possible. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Dangelo/Lambert NEAR TERM...Lambert/Ceru SHORT TERM...Lambert LONG TERM...Gartner/RXR AVIATION...Fitzgerald/Ceru

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