Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 182355
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
755 PM EDT Mon Mar 18 2024

.SYNOPSIS...
An amplifying upper level trough will drift across Pennsylvania
through tonight, followed by a reinforcing shortwave and
associated cold front Wednesday.

High pressure is likely to build over the area Thursday. A
dying cold front is likely to approach from the Great Lakes late
next week, as a southern stream shortwave passes south of the
state.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Water vapor loop at 22Z shows a deep upper level trough pushing
into PA from the Grt Lks. Modest instability ahead of it is
producing mostly light snow showers across the Alleghenies and
central mountains, while dry air and downsloping flow is
maintaining fair but chilly dry conditions across the Susq
Valley.

Large scale subsidence behind the exiting trough should result
in breaking clouds east of the mountains tonight, while lake-
enhanced orographic snow showers persist across the Allegheny
Plateau. Near term model guidance indicates the plume of best
lake moisture will begin the evening over the NW Mtns, then
pivot south into the Laurel Highlands late tonight. Progged
inversion heights are fairly low and the airmass remains dry
outside of lake bands, so overnight accumulations will be light.
Latest ensemble mean qpf supports overnight accums ranging from
a dusting over most of the Alleghenies, to around an inch over
the Laurel Highlands.

A well mixed boundary layer and only weak cold advection suggest
temperatures will fall slowly tonight, with daybreak readings
ranging from the mid 20s over the higher terrain of the
Alleghenies, to the low 30s in the Lower Susq Valley.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
Latest guidance continues to track a clipper across the Northern
Grt Lks Tuesday. Backing flow ahead of this feature should
result in a break in the lake effect activity early Tuesday.
However, warm advection along the attendant low level jet is
likely to support some light snow across primarily the N Mtns
Tuesday. Latest ensemble mean qpf indicates accumulations of
less than an inch are likely. Temperatures will edge up a bit
Tuesday under warm advection regime, but plenty of cloud cover
should still result in max temps several degrees below average,
ranging from the 30s over the N Mtns, to the low and mid 40s in
the southern valleys.

The best isentropic lift shifts north of the border Tuesday
night. However, residual low level moisture ascending the
Allegheny Plateau should result in a few lingering snow showers
overnight in that part of the state, with clearing skies
expected downwind (east) of the mountains.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
The passage of the trailing cold front Wednesday should be
accompanied by scattered rain/snow showers, a few of which
could survive into the Susq Valley, due to strong forcing ahead
of the upper level shortwave. Steep lower tropospheric lapse
rates indicate the potential of some heavier snow squalls
across the N Mtns. Deep cold advection and passage of a strong
isallobaric couplet signal a period of gusty northwest winds
behind the cold front late Tuesday. Latest Bufkit soundings
support gusts in the 30-40mph range late Tuesday into Tue
evening. Fair, but still cool, weather appears likely Thursday,
as the trough lifts out and surface ridging builds in from the
Grt Lks.

Medium range guidance suggests a few rain showers are possible
Friday, mainly over the N Mtns, associated with the approach of
a dying cold front. The bulk of guidance tracks a more
significant southern stream shortwave and associated area of
low pressure well south of PA next weekend. Therefore, fair and
seasonal conditions currently appear likely next Sat/Sun.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
Mainly VFR will continue into Tuesday across much of the
central and SE PA airspace under varying amounts of stratocu
based AOA 3500 ft AGL.

There will be occasional to persistent MVFR across PA`s
northern and western mtn airfields tonight and even some brief
periods of MVFR Cigs at KUNV and KAOO in -SHSN this into this
evening.

West-northwest winds will be moderately gusty this evening and
tonight for all TAF sites.

A dual or multi-layered cloud shield (mainly VFR) will spread
across the region Tuesday as the low level flow backs a bit more
to the west-southwest, helping to confine most of the snow
showers across the far NW zones, with generally mostly cloudy
skies and breezy and dry conditions elsewhere.


Outlook...

Tuesday-Saturday...Periodic snow showers and reductions,
primarily across the higher terrain of northern and western PA.
This will be enhanced by reinforcing shots of unseasonably cold
air and gusty W/NW winds. West to northwest wind gusts could
peak in the 35 to 40 mph range on Wednesday.

&&

.CLIMATE...
Astronomical Spring (vernal equinox) begins on Tuesday March 19
at 11:06 PM EDT.

&&

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

&&

$$

SYNOPSIS...Lambert
NEAR TERM...Fitzgerald
SHORT TERM...Lambert/Fitzgerald
LONG TERM...Fitzgerald
AVIATION...Lambert/Gartner
CLIMATE...Steinbugl


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