Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 120511 AFDCTP Area Forecast Discussion National Weather Service State College PA 1211 AM EST Tue Dec 12 2017 .SYNOPSIS... An alberta clipper will track over northwestern PA late tonight, with a trailing arctic cold front sweeping through the area early Tuesday. A deep upper level trough will remain over the eastern conus through the rest of this week with another weak clipper likely affecting the area Thursday. The upper trough will likely lift out by next weekend. A low pressure system lifting northeast from the Great Plains will bring a southwest flow of milder air for the weekend. && .NEAR TERM /UNTIL 8 AM TUESDAY MORNING/... Only very light snow/flurries S of Route 6 right now and the expected pivot to the best lift is about to start as the low pressure center gets close to KCLE. Have lowered POPs some in the srn half of the area for the overnight as most near-term guidance makes little or no QPF south of Route 22. Prev... Low pressure over IN attm. Good band of snow stretches from Erie back through Rock City to Valpo. Mid clouds from WAA ahead of this is generating a few flurries for the NW, but most of the area will remain only mo/cloudy for the first 2/3rds of the night. As the low center passes over BFD, the wind will pivot and drag a line of snow showers through late tonight/almost to sunrise (per latest CAMs). Little in the way of instability when this first volley is slated to arrive. In fact, the temps may be mild enough that the first volley could be a mix instead of straight snow south of I-80. Prev... Dry and milder conditions prevailing this afternoon thanks to high pressure building into the region. Downsloping subsidence resulting in clear skies across the south central mountains and now working through the southeast while stratocu lingers beneath subsidence inversion over the northwest mountains. Increasing mid and high level cloudiness arriving ahead of clipper over the Great Lakes on schedule, and will continue to thicken late this afternoon and evening as clouds increase farther east and south as well. Model consensus brings a batch of warm advection snowfall to western and northern sections this evening through overnight with a coating to 1 to 3 inches from I80 northward to the NY border respectively. Main impacts from this system will come as the cold front ushers in the coldest air of the season into PA later Tuesday, after FROPA Tue morning. As per collaboration with PBZ and BUF, Winter Storm Watch was already upgraded to Lake Effect Snow Warning for Warren County. Also expanded Winter Weather Advisory southward to include the rest of the Laurels (Clearfield, Cambria and Somerset Counties). && .SHORT TERM /8 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... The coldest air of the season is forecast to arrive behind trailing arctic cold front Tuesday with more lake effect snow lasting through midweek. Northwest Warren County should get into some of the more robust lake effect banding later Tuesday and continuing into Wednesday. Lake Effect Snow Warning in effect for this, per collaboration with BGM, for widespread 10 to 15 inches, with local amounts up to 18 inches over extreme northwest Warren County. Model blended qpf supports a long duration advisory over Elk/Mckean counties, as well as Clearfield/Cambria/Somerset Counties where 4 to 8 inches are expected from 12z Tuesday through 18z Wednesday. Still some concern about snow squalls accompanying cold front passage between 12Z-18Z Tuesday. However, lower tropospheric lapse rates look less impressive than would be expected for a significant snow squall event and are actually separated from the best frontal/isallobaric forcing. Still isolated snow bursts and a few squalls are possible on Tuesday. It appears the Lower Susq River Valley will be spared from any snow squall threat Tuesday since boundary layer temps appear borderline for shra vs shsn and surface temps are likely to be near 40F. Gusty wnw winds will develop Tuesday behind the cold front with bufkit soundings supporting frequent gusts of 30kts+ by late in the day. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... Gusty northwest winds and snow showers will be the main issue Tuesday Night into Wed. Warnings and advisories in effect until 18Z Wed. Models show another system for Thursday. This system looks weak and EC a little further south, as been the case. Thus just have very light amts in. Maybe more of an impact for the far southeast, than system for Tue into Wed. After this the pattern supports a deep low tracking northeast from the Great Plains for the weekend, which will result in milder conditions. As been the case, the Gulf of Mexico is not really open, so looking at a mainly dry weekend. Complex pattern for Monday, perhaps a little light snow, but nothing major. Minor changes to the extended package. && .AVIATION /04Z TUESDAY THROUGH SATURDAY/... Some feeder bands have moved through out ahead of an alberta clipper that will track just north of Pennsylvania tonight. These feeder bands are fairly light and low level stratocu has set up over the region. Brief IFR conditions are possible between 06Z to 08Z. More widespread IFR cigs and vsbys will occur as a trailing arctic cold front sweeps through the area early Tuesday around 06Z at BFD. Between 06Z to 15Z the front will spread from the NW across the state though the worst cigs and vsbys will primarily be over the NW half of CWA. There is some concern about snow squalls accompanying cold front passage between 12Z- 18Z Tuesday. Then gusty WNW winds develop with frequent gusts of 30kts+ by late in the day. Reducing conditions will continue for the western and central TAF sites through most of Tuesday and will slowly improve into Tuesday night, though reducing cigs and vsbys could linger at BFD and JST into Wednesday. Outlook... Late tonight and Tuesday...Periods of light snow - mainly NW half. Widespread MVFR likely, with periods of IFR and brief LIFR cigs and vsbys NW. Wed...Snow showers with IFR NW Mtns. Sct snow showers with MVFR NW half. Otherwise VFR. Thu-Fri...Sct snow showers. Reductions west. Sat...Mainly VFR. Perhaps a snow shower north early. && .CTP WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 7 AM Tuesday to 1 PM EST Wednesday for PAZ005-010-017-024-033. Lake Effect Snow Warning from 7 AM Tuesday to 1 PM EST Wednesday for PAZ004. && $$ SYNOPSIS...DeVoir/Fitzgerald/Martin NEAR TERM...Dangelo/DeVoir/Fitzgerald SHORT TERM...DeVoir/Fitzgerald LONG TERM...Martin AVIATION...DeVoir/Ceru

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