Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 170418 AFDCTP Area Forecast Discussion National Weather Service State College PA 1118 PM EST Tue Jan 16 2018 .SYNOPSIS... Low pressure will pass off the Mid Atlantic coast tonight. In its wake, a deep upper level trough will swing through the area Wednesday, then be replaced by a building east coast ridge by next weekend. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... 02Z regional radar mosaic showing light snow falling over nearly the entire forecast area with snow band enhancement in vicinity of I-81 associated with fgen forcing beneath right entrance region of 130+ kt jet. Latest models indicate light snow will taper off from west to east overnight, with enhanced band of moderate snow linked to jet streak exiting the southeast portion of the forecast area by midnight. Using blended qpf of latest HRRR/NAM and earlier NBM, expect additional accums between 00Z-12Z ranging from less than an inch over the western half of the forecast area, to 3 inches from Sullivan/Columbia/Schuylkill counties. Examination of omega/temp time sections suggest snow/water ratios will be close to 15/1. Snow totals in the 6-8 range appear likely over the Mid Susq Valley/Poconos, just short of 24hr warning criteria, so no changes planned to the current headlines. Breaking clouds and dropping temps will overspread most of the forecast area by dawn, as high pressure and associated low PWAT air mass arrive. NBM/Superblend numbers indicate readings by dawn ranging from the lower single digits over the Alleghenies, to the low 20s over the Lower Susq Valley. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... The back edge of the light snow should taper off by around dawn over the eastern part of the forecast area. Arrival of high pressure and associated low PWAT air mass should result in a mostly day across the central portion of the forecast area. Model soundings indicate cirrus shield may linger over the southeast counties for much of the day, but clearing eventually expected by late in the day. Over the Allegheny Plateau, lake moisture, combined with upslope flow will likely yield some stratocu. However, low inversion heights indicate nothing more than a flurry. Ensemble mean 925mb temps of around -13C support highs no better than the mid teens across the western mountains, to the mid 20s over the Susq Valley. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... The medium range will feature a fairly long period of dry- tranquil weather with soon to moderating temperatures. After an initial reinforcement of cold air that will keep highs below freezing tomorrow, a milder westerly flow will develop as as a surface high slides along the Gulf coast toward the SERN US. By Friday a milder WSW flow will push daytime highs above freezing over most of the forecast area, and temperatures are expected to continue to creep upward into the weekend. Temperatures by the weekend will be well above normal under the building eastern ridge. The next chance for precipitation looks to not be until later Saturday into the overnight with a surge of warm advection that is made to develop with the approach a warm front that should slide up to our west into NY state. The chance of showers favoring mainly western areas will continue through Sunday. There is remarkably good agreement at this range in dragging a significant cold front through the area Monday afternoon or evening. The GEFS takes the best PWAT anomaly up through the eastern lakes mainly west of the CWA and right now shows a generally light-moderate rain event. Of course any kind of warmup accompanied by rain will create ice-jam and flooding concerns so that looks to be the next big threat moving forward. && .AVIATION /04Z WEDNESDAY THROUGH SUNDAY/...
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Area of snow over Central Pennsylvania continues to rapidly diminish this evening. While conditions over much of the region still IFR, starting to see areas of MVFR and even some spotty VFR develop across the Central Mountains region. Expect visibilities to rapidly improve overnight, as light winds shift to the WNW and pick up to 5 to 10 mph. Ceiling heights also improving overnight, but at a much slower pace. Appears that snow will be completely out of the area between 09z and 11z. While mountains of the west and north will hold onto lower cielings into Wednesday, central and eastern areas should become VFR around or by sunrise Wednesday morning. Thursday looks to be breezy with gusts to 15-25 mph. Outlook... Wed...VFR over central and eastern areas, but ceiling restrictions across the Northern and Western Mountains as a result of isolated snow showers. Thu-Sun..Mainly VFR.
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&& .HYDROLOGY... The threat of ice jamming is diminishing. Dry and colder weather into mid week will form additional ice as stream flows and open channels decrease. Another warm up is expected by the end of the week into the weekend with rain to accompany a frontal system early next week. && .CTP WATCHES/WARNINGS/ADVISORIES...
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Winter Weather Advisory until 7 AM EST Wednesday for PAZ036- 051>053-056>059-063>066. Winter Weather Advisory until 4 AM EST Wednesday for PAZ012- 018-019-026>028-037-041-042-045-046-049-050.
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&& $$ SYNOPSIS...DeVoir/Fitzgerald NEAR TERM...Fitzgerald SHORT TERM...DeVoir/Fitzgerald LONG TERM...La Corte AVIATION...Jung HYDROLOGY...

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