Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 181953 AFDCTP Area Forecast Discussion National Weather Service State College PA 253 PM EST Mon Dec 18 2017 .SYNOPSIS...
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Upslope flow 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 /THROUGH TONIGHT/...
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Very moist upslope flow tonight and two weak short wave troughs moving east from the Great Lakes will combine over the next few hours. This will start some showers shortly (say that 5 times, fast) over the NW, then keep them going off and on through the night. Some patchy drizzle is possible in between the somewhat- convective showers. Some fog is possible in locations which still have some snow on the ground. No snow is left in the SE, so advection fog risk is lower there, but they might stay mainly clear and have almost no wind. This tips the scales in favor of radiation fog there. Mins should stay very mild under the clouds and with a little wind over the Alleghenies and central mtns.
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&& .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
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Tuesday/Tues PM look mainly dry, but the clouds will hang around for the NWrn 2/3rds of the area. Fast W-E flow aloft, but systems are to our south and north, and n`er the twain shall meet. However, the northern system shoves a slug of cold air down through the state from the north very late in the day and through Tues night. Maxes on Tues will be balmy 50s in the south, but just a bit above normal in the north - under the clouds. Due to shallow wedge of cold air moving in, the temps at night will drop into the m20s N and m30s S. Any --precip lingering after fropa will turn to flurries.
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&& .LONG TERM /WEDNESDAY THROUGH MONDAY/... 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 /20Z MONDAY THROUGH SATURDAY/...
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Moist upslope flow in the wrn mtns will continue through the entire period. Two upper level short-wave troughs will pass overhead tonight and generate some showers. It will stay mild under the clouds and only rain is expected. VFR conditions in the eastern airfields should continue unless some radiation fog can form. That is possible, since the sky should be mostly clear in the SE tonight, but lower/mid clouds could spill down from the central mtns and make fog formation difficult. KJST and KBFD will stay IFR in cigs and perhaps fog all night and most of Tues. MVFR cigs are expected at AOO/UNV, although they may dip to IFR for a brief time. Temps on Tuesday will get more mild, but a backdoor front dropping down from NY will drop the temps Tues PM, and if any --precip is left over, it would turn to --sn. Outlook... Wed-Thu...No sig wx. Fri...SHRA poss W. Fri PM-Sat...SHRA. IFR poss.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Dangelo NEAR TERM...Dangelo SHORT TERM...Dangelo LONG TERM...RXR AVIATION...Dangelo/RXR

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