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Area Forecast Discussion
||Wed, Dec 31, 7:00pm EST
FXUS61 KCTP 181953
Area Forecast Discussion
National Weather Service State College PA
253 PM EST Mon Dec 18 2017
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.
.NEAR TERM /THROUGH TONIGHT/...
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
.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
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.
.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/...
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
Wed-Thu...No sig wx.
Fri...SHRA poss W.
Fri PM-Sat...SHRA. IFR poss.