Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 192240

Area Forecast Discussion
National Weather Service State College PA
540 PM EST Thu Jan 19 2017

High pressure overhead will retreat and a warm front will push
rain across the state on Friday. Relatively mild conditions
will persist for the next several days. A very complicated storm
system may bring a prolonged period of rain from Sunday into
early next week. Snow or mixed precipitation is also possible
from that same storm early next week.


Clouds breaking up now - esp so in the S. This trend should
continue but the nrn mtns may stay cloudy longest this evening.
In a tricky part of the forecast, some low clouds may form again
later tonight on the higher elevations as SE flow begins ahead
of the warm front approaching. However, the overall cloud
forecast is generally cloudy tonight with high clouds over the
area. As the low levels stay generally clear, the temps may cool
to below freezing in spots like FIG, MUI, THV, and lots of the
area N of IPT.


Warm frontal precip moves in Fri morning around sunrise or a
little later in the Laurels and spreads a band of 3-6hr light
rainfall across the entire area during the daylight hours.
Timing is very solid amongst all models and forecast confidence
is very high. There is one very small trouble with the rain - if
it moves in quickly enough to get to some of those patches where
it will be below freezing, there might be some fzra. However,
most of the places which may dip below freezing will have a bit
of daylight to help it warm up slightly. Also, the wet-bulb
effect could present a minute chance of it freezing up - mainly
over the NE - but again, those areas should have the chance to
warm up enough to keep the fzra threat low. Have not put the
mention in the grids yet. Maxes/diurnal swing will be held down
once again by the cool air trapped and not quite get into the
40s over a good portion of the area - with mid 30s the
expectation in the NE and the central mtns. Even MDT and LNS may
not eclipse 40F.


The upper ridge is forecast to re-establish itself over the
eastern U.S. over the upcoming weekend, bringing mild and mainly
dry conditions Saturday, through at least the mid morning hours on

Daytime temperatures across most of Central Pennsylvania will be
well above normal, but the departures for overnight lows should be
greater by several degrees more throughout the entire extended

The ridge axis will shift to the Hudson Valley and Eastern
Seaboard early Sunday as a sfc backdoor cold front drifts swwd
into PA and stalls out as a potent and moisture laden nearly
stacked low lifts NE from the deep south to the Delmarva region by
12Z Tuesday.

Temps could be marginal at the start of pcpn overnight Sunday for
some ice or snow, and soundings via the GFS/GEFS and EC appear
cold enough for Sunday night through Monday night for a mix of
rain/snow (or even periods of all wet snow at times across the
northern mtns of PA). However, the bulk of pcpn across the
Central Ridge and Valley Region looks to be rain at this point
through Monday afternoon.

The trend in most operational models and ensembles has been
further to the south and east with this particular late
weekend/early week system. This places parts of the fcst area in
the sweet spot for potentially several inches or more of heavy,
wet snow (especially later Monday/Monday night across the nrn and
wrn mtns of PA at elevations of 1400 ft or higher), as the mean
850 mb low in the GEFS and EC tracks NE along the I-95 corridor in
VA and adjacent SERN PA/Southern NJ.

U-wind anomaly at 850 mb peaks at -4 to -5 sigma during much of
Monday as a 45-55kt easterly llj develops between this approaching
low, and the aforementioned colder airmass pushing swwd from SERN
Canada and the New England states. Rainfall amounts are expected
to be in the 1 - 1.5 inch range across roughly the SE half of PA
with lesser amounts to the NW.

Another short wave ridge will slide east from the Ohio Valley and
move over the Commonwealth Wednesday, accompanied by light wind
and fair/generally dry conditions.


Low clouds have cleared out over all but the northern tier of Pa
this evening as the inversion falls. However, the low clouds
may return to the higher elev sites later tonight, as a light
SE flow develops ahead of an approaching warm front. The warm
front will bring lowering clouds from high-mid-low as it
approaches anyway. But the low clouds may form aside from that
more obvious progression. Timing from all models is nearly
identical and leads to very high confidence forecast of rain
timing, beginning about 13z in JST and 17Z in MDT & IPT. There
could be a brief period of IFR at all sites, but esp JST/BFD.
The WAA rainfall passes by 18Z in JST and by 00Z Sat at IPT.
However, low clouds and patches/widespread drizzle are expected
as the moist air sits over the mountains.


Sat...MVFR cigs W/VFR cigs elsewhere.

Sun...Widespread IFR/MVFR restrictions - mainly S. RA advances
fm S-N.

Mon-Tue ...Widespread IFR restrictions in -RA and poss SN on
higher elevations. LLWS poss.




NEAR TERM...Dangelo
SHORT TERM...Dangelo
LONG TERM...Lambert/Gartner
AVIATION...Dangelo/Fitzgerald is the U.S. government's official web portal to all federal, state and local government web resources and services.