Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 021937 AFDCTP Area Forecast Discussion National Weather Service State College PA 237 PM EST Fri Dec 2 2016 .SYNOPSIS... A large and deep storm system will move slowly southeast across northern New England late today and Saturday, keeping a prolonged period of cool northwest flow and a gusty wind over the local area. A ridge of high pressure will slide east across the commonwealth for Saturday night and Sunday accompanied by fair dry weather and light wind. A weak disturbance aloft and surface frontal boundary will cross the region Sunday night and Monday accompanied by some light snow across the northern half of the state...and a period of light mixed precipitation in the south. && .NEAR TERM /THROUGH TONIGHT/... Shallow and relatively warm strato cu deck will continue to blanket practically all of the CWA late today and tonight. little in the way of precip is expected across most of the northern and western mtns of the state this afternoon and early this evening as the mean llvl flow will remain westerly with little tap of significant moisture off the upper Great Lakes. Significant breaks in the cloud deck will occur across the Middle and Lower Susq valley at times, but clouds will spread back across that area between 20-22Z today. The Central Ridge and Valley Region will be in between with mainly and ovc deck high-based strato cu this afternoon and evening with nothing more than a sprinkle or flurry. With the temps mainly in the mid 30s late this afternoon across the NW mtns where frequent snow showers will occur, expect to see less than an inch or snow accumulation, which will be confined to grassy areas for the rest of the daylight hours. Elsewhere over Central and Southeastern parts of the Forecast Area, high temps will be in the low-mid 40s. Some locations to the east of I-83 and south of I-81 could reach 50F during the early to mid afternoon. A 20-30 deg veering of the wind overnight tonight following the passage of a weak sfc/upper level trough will allow for a longer, well-aligned fetch of chilly air across multiple glakes. Combine this with neutral temp advection or slight cooling aloft and increasing/moderately strong NW flow of 35-45 kts in the upper boundary layer means that we should see increasing amounts of NW/SE oriented, thin bands of snow showers streaming well inland across the NW mtns and Laurel highlands, and ocnly spilling into the Central Ridge and Valley Region. A light accum of a coating to one inch should occur across the Laurel Highlands overnight, while the NW mtns (specifically Warren and Mckean counties see snowfall totals of 1-2 inches with locally higher amounts possible north and west of the city of Warren. Additional light snowfall Saturday morning from LES showers could bring 18-24 hour totals to 3 or 4 inches throughout the typical snowbelt of NW Warren County (and perhaps portions of Mckean County). However, these amounts will be just under LES Advisory Criteria of 3 inches/12 hours. NW winds should even increased by 3-5 kts in sustained speeds tonight, and with gusts some 5-10 kts night tonight as the thermally direct subsiding left entrance region of a powerful 160 kt upper jet lifts north across the state. Gusts of 25-30 kts possible, especially across the western high terrain and gaps just east of ridges and along the Allegheny Front. Min temps early Saturday will vary from the upper 20s across the higher terrain of nrn and wrn PA, to the l-m 30s elsewhere. && .SHORT TERM /SATURDAY/... The stacked low pressure over moves over the Canadian Maritimes. The mean WNW boundary layer flow off the Great Lakes will be persistent with multiple narrow bands of mainly lake effect snow expected to spread a little more inland (developing south across the Laurel Highlands) and last into Sat Night. Clouds will be pesky and linger across much of the CWA right through the day Saturday. Max temps Saturday will be slightly colder across the north and west, but slightly warmer than today (Friday) across the Susquehanna River Valley. Still, these numbers are within a few degs of normal for the first part of Dec. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... Late Sat night and Sunday brings a brief respite as high pressure builds east across the state. Sunday evening and night, a period of light snow is looking likely as a northern stream shortwave races through the region with a burst of warm advection. QPF looks to be on the order of a tenth of an inch or less, but occurring overnight many places could see their first coating of snow of the young season by Mon morning. Snow is more likely in the NW than SE. Another ridge moves through on Monday as progressive weather pattern becomes more active. On Tues there is decent agreement in bringing the SW US upper low up through the Ohio Valley 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. 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 /19Z FRIDAY THROUGH WEDNESDAY/... Mid afternoon satellite loop continues to show stratocu covering most of Central PA, associated with slow moving low pressure over Southern Quebec. Cold air flowing over Lk Erie is producing lake effect snow showers across Northwest Pa. Will stick with persistence at KBFD/KJST and forecast predominantly MVFR conditions. However, there will still be ocnl dips to IFR with passing snow showers at KBFD. Downsloping flow east of the mountains should result in progressively better (high-end MVFR and low-end VFR cigs) conditions further east. Mainly VFR at KIPT/KMDT/KLNS, with temporary dips to MVFR cigs overnight. Ocnl snow showers will likely drop vsbys into the 1 1/2SM-3SM range at KBFD/KJST late today through Saturday. The entire region will continue to see breezy conditions last through the next 24 hours. Bukfit soundings support sustained winds between 10-20kts across the entire region today and tonight, with occasional gusts around 25kts (especially late tonight and early Saturday) as mean winds in the lowest 5 kft agl veer by about 20 degrees to around 290 Deg. Outlook... Sat...SHSN with ocnl IFR vsby at KBFD/KJST, mainly in the morning. Sun...Light snow/reduced vis possible at night, mainly NW Mtns. Mon...No sig wx expected. Tue...Mixed precip/low CIGs possible across the nrn mtns, with a mdtly heavy 0.50-1.00 rainfall expected across much of Central and Southern PA. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...La Corte/RXR AVIATION...Lambert

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