Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 180523 AFDCTP Area Forecast Discussion National Weather Service State College PA 1223 AM EST Mon Dec 18 2017 .SYNOPSIS... A shortwave will pass over the area late this evening, generating some spotty, light mixed precipitation along the I-80 corridor. Slightly colder air moves in for Monday, but temperatures will warm a bit for Tuesday. A back door cold front will bring colder air in from the north on Wednesday. Generally dry weather with a warming trend is then expected for the last part of the week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... Late evening radar loop showing spotty, light mixed precip moving into the central mountains ahead of shortwave moving across the state. Near term model data continues to indicate spotty, light mixed precip will affect the I-80 corridor overnight. Based on model soundings, any precip that makes it much north of I-80 should fall as light snow/flurries and radar trends/model data indicate the odds of measurable precip is low across the southern half of the state overnight. Therefore, we are looking at a narrow corridor of potential fzra along the I-80 corridor. Surface temps are very marginal and a quick look at RWIS data shows road temps within this threat area remain a degree or two above freezing, so believe the threat of icing is fairly low, but not zero. Have issued a SPS to account for the potential icy spots. Shortwave and associated large scale forcing wanes late tonight, causing any lingering light precip to taper off. Cloud cover and WAA should hold temps nearly steady overnight across much of the area. However, partial clearing across southern Pa late is likely to allow temps to fall to the lower 30s across that area late tonight. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TUESDAY/... Jet right overhead Monday into Mon night, but very homogeneous at 140-150kts at that point. The lowest 3-4kft of the atmos is what will drive the sensible weather tomorrow. An increasingly moist upslope flow into the wrn highlands will likely cause some light rain/drizzle to develop late in the day. Model soundings indicate the cloud layer should be too shallow to support snow over most of the region, with the possible exception of the NW Mtns, where wouldn`t rule out a few snowflakes late in the day. Maxes will likely range from the m30s under the clouds/DZ in the NW to the mid 40s SC/SE, where partly sunny skies are expected. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Fast zonal flow continues over the region Tue, with a trough swinging by to our north. This will drag a weakening cold front through on Tuesday, keeping mention of rain showers over the NW as a breezy westerly wind develops with 50kt 850mb jet rotating through in association with FROPA. Pattern gets more interesting for mid/late week as high pressure slides across the Great Lakes and pivots by to our north before building into New England, as the same time low pressure develops over the upper midwest (ahead of a trough sliding across the Rockies). Initial impacts will be that Wed into Wed night will be the coldest spell of the week - though Thu night could also be notably below current forecast guidance over eastern portions as high pressure will still be exerting influence there as it slowly drifts further east. This will be followed by a warmup headed toward next weekend as long- fetch SW flow brings WAA to the Eastern Seaboard ahead of the approaching low. Precip slides toward the region Thu night into Fri, before gradually spreading across the region for Fri into Sat. Precip looks to hold off over the west until the day Fri, which led me to drop mention of poss freezing precip Thu night/early Fri. Also, long range guidance is in surprising agreement bringing a surge of WAA to the region starting Friday into Sat as 850/925mb temps rocket to +5-10C Fri night which should lead to fairly mild lows (esp over the SE) and keep precip in the form of rain. The front eventually lifts through on Sat as the surface low lifts into Ontario, leading to just a glancing shot of colder air that will bring a mix of rain/snow showers to northern half, but persistent trough over central U.S. will keep push of WAA ongoing which should continue milder temps over the SE half into early next week. && .AVIATION /05Z MONDAY THROUGH FRIDAY/...
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Moist upslope flow in the NW mtns has allowed for IFR cigs to form at BFD. Expect these conditions to continue through the overnight period and through the first half of the morning Patchy DZ or very light SHRA is all we should see overnight as deeper moisture continues to diminish as ceilings elsewhere continue to lift. A WSW flow will keep a weak upslope flow going into the Alleghenies and Laurels Monday, so patchy DZ/sct SHRA remain likely. The moisture will decrease Monday Night, and the threat of light precipitation should end. Eastern airfields should become VFR tomorrow afternoon, with central airfields right on the MVFR/VFR border. KBFD and KJST will likely be MVFR/IFR for much of the day. Outlook... Tue...Mainly VFR, Iso SHSN NW. Wed-Thu...No sig wx. Fri...SHRA poss W.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Dangelo/Fitzgerald NEAR TERM...Fitzgerald SHORT TERM...Dangelo/Fitzgerald LONG TERM...RXR AVIATION...Ceru

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