Area Forecast Discussion
Issued by NWS State College, PA-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KCTP 201452
Area Forecast Discussion
National Weather Service State College PA
1052 AM EDT Thu Oct 20 2016
A storm system will move into Western Pennsylvania today. The
associated cold front will move slowly across the state tonight
and Friday. Windy and much colder weather will move in for the
weekend with the first bout of lake effect and upslope rain and
snow showers Saturday into Saturday night.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --The meso anal early today shows a very complicated surface
pattern with an inverted trough poking up into NWRN Pa, and cool
air damming scenario in place further east over much of central
and eastern Pa. The warm front aloft extends from the northern
mountains SSE into the lower Susq Valley where marginally
unstable air has helped support showers and isolated
Some locally heavy rains in excess of 1 inch have already been
observed over portions of the northern mountains with radar
estimates in excess of 2 inches over parts of Warren County.
The NW looks to remain the focus for the best rains today as a
wave of low pressure forms over the lower Ohio Valley and ripples
up into western Pa by nightfall. As the associated upper trough
deepens and moves toward the NERN US, the wavy front will slow
down with the best rains concentrating along and behind the front,
in almost classic anafront fashion. The models show a
strengthening upper jet entrance region which will support strong
deep layer frontogenetic forcing moving slowly across the forecast
area, mainly tonight through the first half of Friday.
We are outlooked for a Slight Risk of severe storms which is not
unreasonable given the strong surge of moisture and expected
development of several hundred Joules of Cape by mid to late
afternoon as the front enters western Pa. Model depicted deep
layer shear will be similarly intensifying under the deepening
upper trough so the potential for damaging wind gusts will be
enhanced if any discreet convection can manage to organize.
As far as temps go, right now we already have a very mild - for
the time of year - day forecast. If more sun than is currently expected
manages to break out, we could end up warmer still.
-- End Changed Discussion --
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
The first in a series of surface waves will be lifting out of NW
PA late this afternoon. The surface pattern will be rather
complex by that time with a low and potent cold front moving
slowly across 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.
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. The trough axis takes on a slightly negative
tilt as it chugs from the Ohio Valley...east across Pennsylvania.
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
The amplifying upper trough will dig 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 day with a gusty northwest wind (between 30-40 mph at
times - based on BUFKIT depicted mixing depth up through 6-8 kft
agl in some places). A deep, 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.
.AVIATION /15Z THURSDAY THROUGH MONDAY/...
-- Changed Discussion --A complex low and frontal system will dictate the weather over the
next 2 days.
A warm front will progress through the flying area today with
conditions improving to VFR by mid day or early afternoon where
they have not already. BFD being closest to the front will be the
exception likely holding onto MVFR conditions most if not all day.
The rain will become more widespread later today along with
deteriorating conditions from west to east as low pressure enters
from the Ohio Valley. We will be unstable enough for the possibility
of a potent thunderstorm with strong wind gusts, mainly western
Overnight and Friday will feature widespread MVFR/IFR developing
over the entire region as the wavy slow moving front crawls through
Sat...Scattered showers with restrictions NW. Brisk NW wind.
Sun...No sig wx.
Mon...Mainly VFR. MVFR with rain showers possible NW.
-- End Changed Discussion --
Another new daily record maximum temperature was set at
Here are the current records for 10/19:
Harrisburg: 82 in 1945 (New record set 85)
Williamsport: 82 in 1963 (High temp just shy of the record at 81F)