Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 200204

Area Forecast Discussion
National Weather Service State College PA
1004 PM EDT Wed Oct 19 2016

A weak cold front will move through and stall just south of the
region today. Unsettled conditions will redevelop for the end of
the week as a series of low pressure areas ripple up along an
approaching cold cold front. Brisk and much colder weather will
move in for the weekend.


The meso analysis suggests what`s left of the slow moving front is
pretty much stalled in the vicinity of the Mason-Dixon line. The
most enhanced clouds pretty much depict this feature from SW Pa to
the lower Susq Valley.

Temps are rising quicker than earlier expectations pretty much
assuring more records will fall in the unusually warm and even a
bit humid airmass. Latest update tweaked afternoon max`s up
several degrees across the board.

It will continue mild overnight as the low level flow quickly
turns southerly ahead of the wave that will be approaching from
the midwest. Increasing warm advection will help bring about an
increasing chance for rain the deeper into the overnight we get,
with the best chances for rain by morning being over my western
and northern zones.


The first in a series of surface waves will enter Pa by Thursday
afternoon. The surface pattern will be rather complex by that time
with a low and cold front moving into the western part of the
state, and a warm front extending east before dog-legging down
through the Central Mountains and east to the coastal plain. The
forecast surface based LI`s depict this cool air damming scenario
lasting at least through mid afternoon before we mix out and see
the warm front become established to the NE of the region.

This also complicates the rain forecast with the best chance of
rain for the first half of the day looking to be over NWRN Pa
associated with the increasing frontogenetic forcing under the
strengthening right upper jet entrance region. To the east we
should see a more misty/showery rain overrunning the wedge of
cooler air over most of central and eastern Pa. As we see the warm
air progress north we could actually end up with another very warm
and rain free afternoon over much of the central and eastern part
of the forecast area as the rain concentrates closer to the low
and cold front over western areas.


The models have converged significantly with the timing/strength of
an amplifying upper trough moving into the Eastern U.S. over the
next couple of days. Initial surface low development along a frontal
zone over the OH Valley on Thursday will give way to a deepening low
center that will elongate as it crosses the Central Appalachians and
Mid-Atlantic States on Friday and interacts with another area of low
pressure tracking northeast in the western Atlantic from the Turks
and Caicos Islands. The full range of guidance shows strong low
pressure consolidating and lifting toward New England as its
trailing cold front pushes off the coast by Saturday morning.

The amplifying upper trough will start to take shape on Thursday as
it digs through Mid MS/TN Valley and eventually closes off, taking on
a negative tilt moving through the Mid-Atlantic/Northeast States
Fri-Sat. The right entrance region of 100+kt upper level jet
should be in a favorable position to provide dynamical support and
enhanced synoptic scale lift. Low level 850mb winds accelerate
ahead of the surface low which helps to draw in precipitable water
values +2SD above normal over Central PA into western NY. The deep
layer upward vertical motion afforded by the upper level
divergence and the sustained moisture flux convergence along the
pivoting frontal boundary should result in 24-36 hour rainfall
totals of 2-3 inches across northwest into north- central PA by
Friday night.

A colder and brisk/gusty northwest flow pattern will set up Friday
night into early Saturday with wrap around/deformation precipitation
on the backside of the low giving way to a cold advection lake
effect/upslope shower regime focused downwind of Lake Erie and
over the higher terrain of the Alleghenies/Laurel Highlands.
Surface- 850mb temps will be marginally cold enough to support
rain/snow showers Saturday (and especially Saturday night) over
the NW mtns and Laurel Highlands with a low probability for a
light coating of snow at the highest elevations. Some wet snow
flakes or pellets may even be possible in the lee of the
Alleghenies over the central ridges and valleys especially in
heavier bands/pcpn rates. 25-35 mph wind gusts will add an
additional blustery chill to below normal temps on Saturday.

GFS/EC still show a fast-moving low diving through the Great
Lakes into early next week. This system has low predictability
given it weak state embedded within a progressive WNW flow aloft.

Temperatures will trend noticeably colder/below normal by the
weekend with highs easily 20-25 degrees colder than today. The
roller-coaster up and down swing in temperatures is not uncommon
for this time of year and will only continue as the calendar turns
towards winter. Overall the pattern looks to stabilize into early
next week with temperatures returning to normal for late October.


VFR conditions prevail this evening across Central Pennsylvania.

A developing storm/frontal system over the Ohio Valley will
spread low clouds and rain into the western mountains
overnight...with more showery precipitation reaching the central
mountains near dawn.

Thursday will feature morning rain and showers, most widespread in
the north and west, tapering to more showery activity before a
larger scale rain event will bring widespread rain and flying
reductions to much of the region Thursday Night and Friday. Once
again, heaviest precipitation, and most significant reductions in
conditions, will be across the west and north.


Thu-Fri...Rain and showers with widespread reductions in
conditions, with lowest ceilings in the north and west.

Fri...Widespread rain and restrictions in flying conditions.

Sat...Scattered showers with restrictions NW. Brisk NW wind.

Sun...No sig wx.

Mon...Mainly VFR. MVFR with rain showers possible NW.


Another new daily record maximum temperature was set at
Harrisburg today.

Here are the current records for 10/19:

Harrisburg: 82 in 1945 (new record set 85)
Williamsport: 82 in 1963




NEAR TERM...La Corte
LONG TERM...Steinbugl
AVIATION...Jung/La Corte
CLIMATE...Steinbugl is the U.S. government's official web portal to all federal, state and local government web resources and services.