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Area Forecast Discussion
National Weather Service State College PA
1143 AM EST Sat Dec 3 2016

.SYNOPSIS...
High pressure will build in later today but slide quickly off to
the east on Sunday. A weak frontal boundary passing through Sunday
night will cause light snow in the north and rain or snow in the
south. A storm with mainly rain may affect the area during mid-
week, some mixed precipitation may occur at the beginning of that
storm.

&&

.NEAR TERM /UNTIL 7 PM THIS EVENING/...
1030 AM update... 
Widespread stratocu will persist through the afternoon hours as
slowly decreasing, deep cyclonic flow combines with broad large
scale lift beneath the right entrance region of an anomalously
strong 170-180kt upper jet lifting north across the state attm. 

Well-aligned flow on an approx 310 deg axis in the lowest several
kft agl will maintain several narrow bands of light snow/rain
showers across the NE half of the CWA thanks to a tap of llvl
moisture with a fetch over a fairly long axis of lake erie. 

Pops in the chc to low likely category were still limited to
mainly the higher terrain to the north of I-80, though some very
light rain and snow showers will reach about 20-30 miles south at
times with QPF of 0.01 or 0.02 possible in a few locations. a
light additional coating of snow is possible at elevations over
2000 ft MSL, otherwise, sfc temps are too warm and precip rates
generally to light. 

Current temps are on track to reach highs in the mid to upper 30s
across the nrn and western mtns and 40s throughout the central and
SE zones. 

The brisk northwest wind will continue, before slowly abating late
today/this evening as a ridge of high pressure builds in from the
Ohio Valley. 

&&

.SHORT TERM /7 PM THIS EVENING THROUGH MONDAY/...
Flow relaxes tonight as sfc ridge slides overhead for Sunday
morning. Some decrease in cloud coverage is expected overnight
(mainly over the SE half of the CWA), but it turns right around
during the day on Sunday. A solid bkn-ovc mvfr to IFR stratocu
deck may linger for much of the night across the Alleghenies of
northern and Western PA.

High/mid/low cloud progression will darken things again wherever
breaks/clearing does occur. The E/SE will stand the best chance
for complete clearing. Temps will be cooler tonight without so
much wind to keep us well-mixed.

Biggest challenge in this cycle is what kind/how much precip falls
Sunday night from the passage of a weak front. All the models and
most of the GEFS members crank out 0.05-0.20 inches of QPF for Sun
night as the feature is carried steadily through by mainly zonal
flow. Most of the precip should be snow, but it is not likely to
stick in many places SE of the Allegheny Front. Just the highest
hill tops of the SE may get a dusting. For a few runs, a weakness
exists in the QPF right through Central PA from W-E. This seems to
be a disconnect between the moisture and the left-exit region of a
150kt jetlet which passes right over the state. Temps are marginal
for accums, and QPF is light. Have drawn 1-2 inches across the
nrn tier of counties. It is a nighttime event, and temps in the
nrn tier are much more likely to be sub-freezing all night.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
There is decent agreement in bringing the SW US upper low up
through the Ohio Valley on Tuesday as a shearing out shortwave
and diffuse surface low. Unless cold air damming traps enough
chilly air in the low levels to make for some freezing rain, the
precip type with this midwest system looks to be mainly rain. Have
raised POPs into the categorical range as it seems unlikely that
we will get missed. 

The end of the week brings some model disagreement with the
GFS/GEFS being faster than the ECMWF with the next large upper
trof and frontal system. Either way, precip looks like a good bet
around the Thu/fri period as all solutions eventually bring this
trough through. So predictability is increasing, but timing issues
remain. Best bet for precip at this point is mainly rain over the
SE as decent push of warm air lifts ahead of the system, with a
rain/snow mix further north where warm air will not infiltrate as
much.

Behind the trough, looks like a chilly weekend in store with a
potential sharp dropoff in temps.

&&

.AVIATION /16Z SATURDAY THROUGH WEDNESDAY/...
16Z satellite loop shows widespread, mainly non-precipitating 
shallow/warm stratocu blanketing all central PA taf sites. 

CIGs ranging from IFR at KJST to low MVFR at KBFD, with VFR between
4-5kft at the lower elevation Central PA airfields, including
KIPT/KMDT/KMDT. These conditions will likely be very stable
through at least 00Z Sunday, if not through much of tonight as the
flow within the lowest 3-4 kft agl stays quite well-aligned from
about 290 deg with a feed of llvl moisture off Lake Erie.

This moist WNW flow forced to ascend the Appalachians will create
borderline IFR/low MVFR CIGs and occasional snow showers.
Downsloping flow will result in progressively better conditions
further east, with MVFR cigs likely at KUNV/KAOO and VFR
conditions at KIPT/KMDT/KLNS.

High pressure approaching from the west will cause snow showers to
diminish across the NW Mtns later today. However, model soundings
still indicate persistent MVFR CIGs at KBFD/KJST through this
evening.

WNW winds should continue to gust between 15-22kts through mid
afternoon, followed by gradually diminishing winds this evening
as high pressure builds in.

Outlook...

Sun...Light snow/reduced vis possible at night, mainly NW Mtns.

Mon...No sig wx expected.

Tue...Mixed precip/low CIGs possible, especially late. 

Wed...Lingering low CIGs possible.

&&

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

&&

$$
SYNOPSIS...Dangelo/Lambert
NEAR TERM...Lambert/Ceru
SHORT TERM...Lambert 
LONG TERM...Gartner/RXR
AVIATION...Fitzgerald/Ceru

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