Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 151912 AFDCTP Area Forecast Discussion National Weather Service State College PA 212 PM EST Fri Dec 15 2017 .SYNOPSIS... A weak upper level disturbance will swing down across the region today as a surface low forms over the Outer Banks and tracks out to sea. High pressure and a brief moderating trend in the temperature are expected by Sunday. A series of cold fronts will move across the area late Sunday into Wednesday. Windy and colder temperatures will follow. && .NEAR TERM /THROUGH TONIGHT/... A fairly potent upper level shortwave/Alberta clipper is diving SE out of the Gr Lakes. Forcing in the favorable left front quad of the upper jet streak is helping support a brief period low level convergence/frontogenetic forcing and fairly widespread - but light snow. CAMs suggest the best chance for a coating to an inch or so of snow will be over my SERN zones where advisory criteria is small and travel issues common with even light snowfalls. At this point it doesn`t seem to warrant a headline, but we did issue a Special Weather Statement to alert for the potential of locally slippery travel. Models use the shortwave to develop a weak surface wave over coastal NC and speeding it well offshore later today and overnight bringing a quick end to the SERN snows. Moisture will also increase over the northwest throughout the day as cold front approaches. That will bring increasing snow shower chances the deeper into the day we get. As the winds shift more westerly behind the upper trough this evening and overnight, cold flow over the lakes will become more favorable for lake effect snow showers. The flow will favor a more westerly than NWLY direction suggesting the best snows will stay closer to the lake, mainly affecting NRN Warren and McKean counties. Lows in the teens and 20s will average about 3-6 deg colder than normal. && .SHORT TERM /SATURDAY/... Lake effect snow showers will continue Saturday morning, tending to diminish during the afternoon as large scale subsidence begins to develop under rising heights aloft. It will still be colder than normal with highs ranging from the upper 20s northwest to around 40 over the south. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
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This coming week will see the long-wave upper level trough that has been dominating out weather shift east as a deep trough digs over the Western U.S. Lake enhanced snow showers should be ending by Saturday night with the surface high pressure ridge moving off the coast and the winds becoming move west to southwesterly. The western trough kicks a strong shortwave out across the Plains Sunday into Monday. The associated low center will move northeast across the Great Lakes staying to our North and west. This system will bring in warmer air in southwest flow ahead of it. However, we may be cold air dammed near the surface so the +1 to -2C air at 850 hPa may not translate to a warm boundary layer. The warm advection should bring snow and snow to rain in the south but QPF amounts are light. Will have to watch for potential for some ice also Sunday night. We look to move into a fast moving pattern of weak shortwaves and chances for precipitation (mainly over the northern mountains) through the week. As a northern stream wave zips by to our north by Monday night, it should drag cold air back into the region Tuesday into Wednesday. The northwest flow triggers snow in relatively high POPS in NW PA due to LES. This cold surge should be relatively fleeting and high pressure and a potential surge of relatively warmer air follows Thursday. The warm advection and approaching cold front will likely produce increased potential for snow in NW Thursday into Friday. Farther south any precipitation would likely be mixed or rain. A strong frontal boundary will likely push another surge of cold air into the region Friday into Saturday as the eastern long wave trough tries to re-establish itself.
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&& .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/... * Cloud/Ceiling info will be missing at KBFD until new part can be installed * Areas of light snow and pockets of MVFR/IFR over central and eastern terminals will continue into the late afternoon with improving conditions between about 21-00Z. Over the NW the flow will take on more of an over-lake trajectory which will bring occasional snow showers into the normal snow belt areas and Laurel Highlands. Expect mainly VFR conditions with locally IFR/LIFR under heavier bands of snow showers. Outlook... Sat...Scattered snow showers and local restrictions NW/Laurels. Sun-Mon...Mainly VFR. Tue-Wed...mainly VFR, but possible restrictions in the western and northern mountains in snow showers. && .CTP WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 7 PM this evening to 4 PM EST Saturday for PAZ004-005. && $$ SYNOPSIS...La Corte NEAR TERM...La Corte SHORT TERM...La Corte LONG TERM...Watson AVIATION...La Corte

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