Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 182057 AFDCTP Area Forecast Discussion National Weather Service State College PA 357 PM EST Sat Nov 18 2017 .SYNOPSIS... Low pressure near Toledo, Ohio late this afternoon will move northeast and intensify over the Lower Great Lakes tonight. A strong cold front trailing south from this low will plow east across the Commonwealth. Colder air with strong, gusty west to northwest winds, and some lake effect snow will then affect the area Sunday. Conditions will gradually improve into Monday. High pressure will bring moderating temperatures and dry conditions Tuesday through at least Friday. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... A large swath of moderate to heavy rain (lifting gradually NE across the NW mtns the Central Mtns and Lower Susq Valley) was being generated by moderately strong south to swrly Isentropic upglide within the 285-290K theta layer, at the nose of a 60 kt 850 mb swrly jet. Sfc temps are struggling to reach 40F this afternoon throughout the deepest central valleys of the CWA, while other locations across the Wrn Mtns and Lower Susq will slowly creep through the lower and mid 40s this evening, before peaking right ahead of the approaching Cfront that`s progged to push across the Wrn Mtns of PA around midnight, and 07-09Z Sunday across the Central mtns and Susq Valley. Expect a sharp drop in temps after the cfropa, and a quick increase in wind as an area of 7-9 mb/3hr sfc pressure rises moves NE from the Ohio River Valley to the Finger Lakes and Pocono region of NEPA between 05Z-14Z Sunday. The Wind Advisory previously in effect for the SW Mtns has been expanded to cover the entire CWA late tonight through 17Z Sunday. A Winter Weather Advisory for LES has also been issued for Warren and McKean Counties in the NW snowbelt from 09Z-18Z Sunday. The layer below 850 mb stays quite stable across the central and eastern 2/3rds of the CWA until just ahead of the Cold front late tonight, when Lifted Indices AOA 850 mb dip to slightly below zero, supporting a slight chance for a few TSRA. An expanding region of elevated instability from Ecent Ohio (that`s currently producing TSRA between I-70 and I-80), that will move over about the SW half of PA late this afternoon/early tonight. Included chc TSRA along with the predominant Periods of light to moderate Rain. Will continue to advertise a large area of 1-1.5 inch rainfall amounts across the region of Central PA and northern PA from along the 22/322 corridors and points north, where models show a stripe of enhanced QPF from the steepest ascent of the moist and increasing unstable air over the persistent/nearly stationary llvl boundary. The rain should become lighter and more intermittent across the southern 1-2 layers of counties of PA for a while this evening as the warm front lifts a bit more to the north. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/... A very windy and cold day is on tap for Sunday with frequent gusts of 40 to 50 mph during the mid to late morning hours as the area of strong 3-6 hourly pressure rises moves NE across the region. SREF mean 850 mb temps of about -7C across the NW and -4 to -5C across the SE support max temps in the l-m 30s INVOF KBFD and KJST and mid to upper 40s INVOF KMDT and KLNS with upper 30s to low 40s throughout the Central Mtn zones. Scattered to numerous snow showers will bring a coating to 2 inches of wind whipped snow accum across the Laurels and northcentral mtns, while the NW Snowbelt receives 3-5 inches of LES. SE of the Allegheny Front, frequent flurries and a few narrow, sinuous bands of snow showers/squalls could whiten the ground quickly in some locations. Some peeks of sunshine will mix in across the Lower Susq Valley at times, with some brief, mixed rain/snow showers. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
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The extended part of the forecast will see the season`s first real lake effect snow event winding down early in the period, followed by several days of cool but tranquil weather. Model soundings show the inversion heights falling quickly Sunday evening through Monday morning, which will begin the process of shutting off the lake effect machine. Look for accumulating snow to continue overnight over the normal snowbelt areas of the NW and even down into the Laurels-with lesser amounts. The snows will continue shrinking back closer to the immediate vicinity of the lakes by Monday morning and by Monday afternoon there should be little more than a few leftover flurries as the high builds off to our south and we see the thermal advection switch from cold to warm. High pressure will keep conditions dry into Tuesday before a weakening front sliding by to our north brings the small chance of a snow shower to northern areas Tuesday night and Wednesday. Another area of high pressure will build east and keep us mainly dry at least through the end of the week, before a new frontal system takes aim at the area.
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&& .AVIATION /21Z SATURDAY THROUGH THURSDAY/... Poor flying conditions are expected to continue through at least the first half of tonight across much of the region with widespread MVFR and frequent dips into the IFR CIG/VSBY range as a warm front lifts slowly NE across PA with shallow cool air trapped in the deep valley of Central and Northern PA until the passage of a strong cold front around 05-06Z across TAF sites KJST and KBFD, then 07-09Z Sunday over the Central Valleys Susq Region. Borderline LLWS will continue until the CFROPA as a potent 50-60 kt southwesterly wind max tops the stable colder airmass entrenched up through a few kft AGL. Periods of rain will continue through the first half of tonight across the west and into the early morning hours Sunday across the East. Southerly winds may become gusty late this evening over the western and southern airspace, as strong winds aloft begin mixing to ground level. Latest NAM/HRRR suggests gusts in the 25-30kt range are possible between 00Z-06Z Sunday. Some of the ridge tops over the Laurel could see south to SSW wind gusts topping 40KTS early tonight as the warm front lifts north of that region and allows better vertical mixing of the higher wind speed air from aloft. Outlook... Sun...Windy with frequent gusts 35-40kts from 270-300 degrees. IFR snow showers NW trending MVFR central to VFR east. Mon...AM shsn/reduced vsbys possible NW mountains. Tue-Wed...No sig wx expected. && .CTP WATCHES/WARNINGS/ADVISORIES... Wind Advisory from 4 AM to noon EST Sunday for PAZ006-012-018- 019-026>028-035>037-041-042-045-046-049>053-056>059-063>066. Wind Advisory from 1 AM to noon EST Sunday for PAZ010-011-017. Wind Advisory from 7 PM this evening to noon EST Sunday for PAZ024-025-033-034. Winter Weather Advisory from 4 AM Sunday to 1 PM EST Monday for PAZ004-005. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Dangelo LONG TERM...La Corte/Lambert AVIATION...Fitzgerald/Lambert is the U.S. government's official web portal to all federal, state and local government web resources and services.