Area Forecast Discussion
Issued by NWS State College, PA

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758 FXUS61 KCTP 180953 AFDCTP Area Forecast Discussion National Weather Service State College PA 453 AM EST Mon Dec 18 2017 .SYNOPSIS...
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Cloudy conditions will prevail today as a mild and fairly moist Pacific flow resides over the northern United States. Patchy very light rain or drizzle is expected from the Alleghenies westward, while the remainder of central Pennsylvania remains dry. 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 through Thursday, before a wet and mild storm system arrives for Friday afternoon and night.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/... Early morning radar loop shows dwindling light precipitation echoes over central PA as shortwave exits to the north. Areas of fog extend from the Ridge and Valley region through the Central Mountains westward through the Northwest/West Central Mountains and Laurels. After a morning lull, an increasingly moist upslope flow into the wrn highlands will likely cause some light rain/drizzle to develop later this afternoon and this evening. 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. Sfc temperatures will be above freezing, so will indicate mainly R-- or patchy drizzle this afternoon into this evening. Maxes will range from the mid 30s in the NW to the mid 40s SE where partly sunny skies are expected. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... Upper trof will swing through the region this evening delivering slightly drier air aloft and continued upslope into the Alleghenies. Patchy R-- and drizzle will persist as a result, with partly to mostly cloudy skies expected elsewhere. Mins under extensive cloud cover will be fairly homogeneous in the mid to upper 30s throughout. Milder conditions are expected on Tuesday with dwindling POPs as H5 forcing shifts southward. Drier air eventually starts to work in aloft late in the day over the northwest. Much of central PA will remain on the cloudy side, but downsloping should promote some partial clearing in the far south and southeast. This will help boost highs into the mid 50s south...while highs up north top out around 40F. && .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 /10Z MONDAY THROUGH FRIDAY/... 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. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...DeVoir NEAR TERM...DeVoir SHORT TERM...DeVoir LONG TERM...RXR AVIATION...Ceru

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