Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 032031 AFDCTP Area Forecast Discussion National Weather Service State College PA 331 PM EST Sat Dec 3 2016 .SYNOPSIS...
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High pressure over the Ohio Valley will build east across the region tonight and Sunday. A weak frontal boundary passing through Sunday night will cause light snow in the north, and a mix of 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.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Widespread stratocu will persist through the rest of the afternoon and most of the overnight 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 will be limited into this evening across 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. Any clearing of the lower/stratocu deck tonight will be topped by increasing cirrostratus, then altostratus from the SW. Current 19Z temps are within a deg either side of fcst high temps...ranging from 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 and veering slightly to the west late today/tonight as a ridge of high pressure builds in from the Ohio Valley. Temps will be cooler tonight without so much wind to keep us well-mixed. Expect lows in the m-u 20s across the mtns, and generally lower 30s elsewhere.
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&& .SHORT TERM /SUNDAY/...
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Thickening High to mid...then low cloud transition will occur on Sunday as a fairly fast moving upper vort max and sfc trough in the northern stream moves east from the Ohio Valley. Biggest challenge still surrounds what exact type and how much precip falls Sunday night from the passage of the relatively weak system. All the models and most of the GEFS members continue to display anywhere from 0.05-0.20 inches of LEQ QPF for Sun night. Most of the precip should be snow, but it is not likely to stick in many places SE of the Allegheny Front where sfc temps will be around or just above freezing. Just the highest hill tops of the SE may get a dusting. Similar to the past few model runs, a weakness exists in the QPF somewhere across central or ncent PA from W-E. Since the core of the nearly East/West upper jet, this seems to be reasonable, since some locations across our CWA will be impacted by the descending branch/right exit region of another (150kt) branch of the jet moving in from the Ohio Valley. Temps are marginal for accums, and QPF is light. Have maintained the 1-2 inches of snowfall 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.
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&& .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... 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 /20Z SATURDAY THROUGH THURSDAY/...
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19Z satellite loop shows widespread, mainly non-precipitating shallow/warm stratocu blanketing all central PA taf sites. CIGs ranging from lower end 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 03Z Sunday, if not through most 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. Evening though the mean llvl flow backs a bit more to the West late tonight...this still moist flow will be forced to ascend the Appalachians will create borderline IFR/low MVFR CIGs and occasional light snow showers. In contrast, the downsloping flow will result in progressively better conditions further east, with MVFR cigs likely at KUNV/KAOO and VFR conditions at KIPT/KMDT/KLNS. WNW winds should continue to gust between 15-22kts through 23-01Z followed, by gradually diminishing winds this evening as high pressure builds in. Outlook... Sun...Thickening and gradually lower cloud deck from mid to high-level overcast...to stratocu and nimbostratus. Light snow/reduced vis possible at night, mainly NW Mtns. Mon...No sig wx expected. Monday night and Tue...Mixed precip/low CIGs possible, especially late. Wed...Lingering low CIGs possible. Wed night and Thursday...strong cold front pushes east across the region with widespread mvfr in showers and mixed precip, then areas of significant reduction in mtn upslope snow showers and localized Lake Effect snow respectively from KJST to KBFD.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Gartner/RXR AVIATION...Lambert

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