Area Forecast Discussion
Issued by NWS State College, PA

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935 FXUS61 KCTP 111926 AFDCTP Area Forecast Discussion National Weather Service State College PA 226 PM EST Mon Dec 11 2017 .SYNOPSIS... An alberta clipper will track just north of Pennsylvania tonight, with a trailing arctic cold front sweeping through the area 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. && .NEAR TERM /THROUGH TONIGHT/...
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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).
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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 collab 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.
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&& .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Model soundings suggest wind advisory criteria is possible early Wed, as large scale subsidence and pressure fall/rise couplet moves through. Have added blowing/drifting to the forecast, where sig snow is expected over the northwest mountains. Base of upper trough and coldest air will be over the region Wed, with temps likely not reaching 20F over the Allegheny Plateau and only reaching the upper 20s across the LSV. Lake effect snow is likely to abate late Wed, as weak surface ridge builds in from the Grt Lks. Med range guidance indicates another clipper is likely to affect the area Thursday with another potential light snowfall. After that, ECENS and GEFS both indicate upper trough will lift out, resulting in a marked warm up next weekend. Latest EC ensemble MOS guidance indicating temps returning to near or slightly above climo by next weekend. && .AVIATION /19Z MONDAY THROUGH SATURDAY/... Mainly VFR conditions prevailing this afternoon, with a scattered to broken deck between 5000 and 12000 feet. Winds will be westerly at 5 to 10 knots. An alberta clipper will track just north of Pennsylvania tonight, with a trailing arctic cold front sweeping through the area Tuesday. Light snow will begin to impact NW mountains after midnight, and spread into the NW half around 10-14z Tues. The snow will be accompanied by cig/vsby reductions - again primarily over the NW half of CWA. 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. 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. && .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 NEAR TERM...DeVoir/Fitzgerald SHORT TERM...DeVoir/Fitzgerald LONG TERM...Fitzgerald AVIATION...DeVoir/RXR is the U.S. government's official web portal to all federal, state and local government web resources and services.