Area Forecast Discussion
Issued by NWS State College, PA-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KCTP 200029
Area Forecast Discussion
National Weather Service State College PA
729 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.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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.
.SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
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.
.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
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
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.
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --Low clouds have cleared out over all but the northern tier of Pa
this evening, as the inversion falls. GLMP MELD suggests low
clouds may break up at BFD around 06Z. However, given the
00Z sfc relative humidity at BFD of 100 pct, expect any
clearing late tonight to result in fog. Elsewhere, upstream
observations and latest near term model data support widespread
VFR conditions through at least 06Z. A moistening southeast flow
late tonight could result in some IFR stratus developing at JST
late tonight and MVFR possible at UNV/AOO.
An approaching warm front will bring a period of rain and low
CIGs to the entire region on Friday. Based on current model
data, arrival time of rain should range from 12Z-13Z at JST to
17Z-18Z at IPT. The rest of central Pa should see rain/low CIGs
develop in between those times. The steady rain will exit the
area between 20Z-00Z. However, low clouds/drizzle are expected
to linger into the evening over most of central Pa.
Sat...Low CIGs likely, mainly in the morning.
Sun...IFR/MVFR CIGs likely. Rain advances fm S-N.
Mon...Rain/low CIGs likely with snow possible central Mtns.
Tue...AM rain/snow and low CIGs possible.
-- End Changed Discussion --