Monday, December 18, 2017, 5:12 PM EST
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Area Forecast Discussion
Valid At
Wed, Dec 31, 7:00pm EST
FXUS61 KCTP 182135
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
435 PM EST Mon Dec 18 2017

.SYNOPSIS...
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 /UNTIL 6 AM TUESDAY MORNING/...
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.

&&

.SHORT TERM /6 AM TUESDAY MORNING 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. 

CAA on Wed as a trough slides by to the north followed by a weak
shortwave in quick zonal flow. Weaker CAA continues into Thu as
a surface high pressure area slips by and then builds over New
England. These will be the coldest days of the week dip to near
or slightly below normal. 

By Friday, trough over the Rockies lifts toward the Great Lakes,
with surface low pressure area deepening to around 1000MB as it
also lifts through the Ohio Valley just to our west. Accompanied
by strong WAA on long-fetch increasing SW flow, expect a warm-up
Fri and Sat. Precip does slide toward the region by early Fri, 
before gradually spreading across the region during the day Fri
into Sat. Precip may begin as a period of light snow or freezing
rain over mainly northern mountains before WAA turns all preci
to plain rain. 

This low lifts toward the Canadian Maritimes by Sunday as
deepening trough is reinforced over the northern Plains. Bit of
an interesting forecast over Xmas as extended models do place a
weak low over the mid-atlantic region on Monday (along stalled
boundary from cold front earlier in the week). Still looks like
we'll have enough warm air in place to bring chances for rain
SE and a rain/snow mix further NW before colder air swings in
from the west for midweek. But light accums not out of the
question over NW half of CWA on Xmas.

&&

.AVIATION /21Z 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
--sn.

Outlook...

Wed-Thu...No sig wx.

Fri...SHRA poss W.

Fri PM-Sat...SHRA. IFR poss.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...Dangelo
NEAR TERM...Dangelo
SHORT TERM...Dangelo
LONG TERM...RXR
AVIATION...Dangelo/RXR

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