Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 180545
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1245 AM EST Mon Dec 18 2017

.SYNOPSIS...
A shortwave will cross the region overnight, 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/...
Early morning radar loop continues to show patchy light rain
over portions of the Central and South Central Mountains, thanks
to 5h shear axis overhead and weak return flow around northern
New England anticyclone. Near term HRRR indicates a few more
hours of light spotty precip, perhaps mixed along and north of
I80...into the pre dawn hours.

Based on the 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. Farther south,
surface temps are very marginal and RWIS data shows road temps
remaining a degree or two above freezing. Shortwave and
associated large scale forcing wanes by08z, 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 /06Z 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...Dangelo/Fitzgerald
NEAR TERM...DeVoir/Fitzgerald
SHORT TERM...Dangelo/Fitzgerald
LONG TERM...RXR
AVIATION...Ceru



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