574
FXUS61 KCTP 071521
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1121 AM EDT Tue May 7 2024

.SYNOPSIS...
Central PA will remain in the vicinity of an oscillating frontal
boundary through Wednesday morning, with one area of low
pressure along the front passing north of the state early
Wednesday. Another, more significant, wave of low pressure will
pass south of PA Thursday. An upper level trough will then pivot
into the region late this week into next weekend, cooling
things down a bit, with temperatures near to slightly below
normal.

&&

.NEAR TERM /THROUGH TONIGHT/...
Slow moving frontal boundary across southern PA late this
morning will drift north through the day, helping to lift/thin
out the low clouds and lingering light fog/haze that`s been
trapped beneath the shallow and relatively weak, near-surface
based inversion.

RAP`s sfc-based CAPE to the south of the aforementioned front
were between 500-1000 J/KG, but shouldn`t increase much this
afternoon as a few deg C of warming aloft and meager mid level
lapse rates advect east over the CWA.

Plenty of sunshine will persist across the northern half of PA
while variable amounts of clouds occur near and to the south of
Interstate 80.

Temps through the rest of today will be unusually uniform from
the higher terrain of northern PA to the typically warmer
valleys in Southern PA, with highs in the low to mid 70s and
roughly a 5 deg F or less spread. The temps will be 4-9F above
normal with the greatest departures seen over the northern tier
with much more sun there than in the South.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
Low pressure will move toward PA and wrn NY this evening,
crossing the area overnight. PWAT values and CAPE will increase
through the middle of the night and numerous SHRA/TSRA are
expected with the greatest coverage and intensities over the W
in the warm sector where the LLJet peaks in the evening and
early night. Intense/near-severe storms shouldn`t get much
farther east than a BFD-UNV-AOO line. SPC has placed the SWrn
corner of the CWA into the MRGL risk for svr wx as a cold front
plows thru overnight.

Tonight should be very warm for early May due to the clouds and
mild southerly flow before the cold front passes later at night.
Mins in the L60s will cover most of the CWA.

Model guidance tracks the weak surface low north of PA Wednesday,
with a weak trailing cold front coming through during the morning
hours. Any morning showers should give way to increasing sunshine,
as drier air works in behind the front. Model 850mb temps near
15C support highs ranging from the mid and upper 70s over the N
Mtns, to the low and mid 80s in the valleys of Central/Southern
PA.

Unsettled weather will return Thursday, as an upstream trough
approaches from the Grt Lks. Latest guidance tracks the associated
surface low south of PA, resulting in a rainy/cool Thursday, with
elevated convection and a marginal risk of severe wx along the
southern tier counties. Will likely be undercutting NBM temp
guidance Thursday if current model trends hold. Raw operational
model surface temps struggle to reach 60F over parts of the
area Thursday. Latest ensemble plumes indicate most likely rain
totals Thursday of around a half inch.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
A notable trend toward cooler conditions for late this week
through the coming weekend as a broad trough develops over the
Glakes and Eastern U.S. with several smaller scale shortwaves
moving southeast within the northern branch of the upper jet.

The surface low and deepest moisture is progged to shift east
of the area Thursday night. However, falling heights ahead of
the positive tilt upper trough (and cold 700 mb temps falling to
around -4C) will likely support scattered-numerous, mainly
diurnal showers Friday through Sunday. A low-topped tsra cannot
be ruled out Friday afternoon/early evening.

GEFS mean 850 mb temps slip to between +2 and +4C (or about -1
sigma) Friday night through Saturday, before rebounding a few
deg C Sunday into Monday. Mean 925 mb temps of just 8-10C later
Friday through Sat morning will likely top even cooler LLVL air
under cloudy conditions.

This cool airmass (with Canadian origin and trajectory over
Lake Erie waters still in the upper 40s to around 50F) will
combine with numerous late morning through early evening showers
across at least the Central and Northern part of the CWA Friday
to likely yield the coolest day we`ll see til this Autumn with
high temps staying in the U40s in some spots across the Northern
Mtns. Highs in the mid 50s to mid 60s will be common heading
southeast from the Allegheny Front.

Temps will still be 2-5 deg F below normal over the upcoming
weekend with mins at night near to a few deg F above normal due
to varying amounts of clouds and at least a light breeze, which
should limit any potential for frost to the patchy variety and
confine it to the Northern Mountains Sat, Sun and Mon mornings.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
Fairly widespread and locally dense fog and a low stratus deck
that occurred early this morning across south central PA
(near and to the south of a warm front), dissipated/lifted to a
5-7SM hz and CIGS AOA 1500 FT AGL.

Most or all of central PA will see VFR conds by 17Z today
afternoon afternoon, with a few pockets of MVFR cigs in
southern PA.

Isolated to scattered -SHRA will be possible during the day.

A warm front will lift northeast across western and central PA
this afternoon and night, leading to a trend toward increasing
areal coverage of showers and thunderstorms and a higher
frequency of MVFR and brief IFR conditions, especially after 00z
Wed.

Marginal LLWS will be possible, but left it out of the TAFs for
now, as confidence is low. Drier air will begin to work into
the western airfields around 12z Wed, but sfc fog may develop
prior to sunrise as the low level moisture is slow to scour out.

Outlook...

Tue...AM low cigs/showers possible southern tier of PA.
Scattered evening tsra impacts possible W Mtns.

Wed...AM low cigs/tsra possible.

Thu...Periods of rain/low cigs likely. Scattered afternoon
TSRA.

Fri and Sat...Showers with periods of low cigs possible.

&&

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

&&

$$

SYNOPSIS...Lambert/Dangelo
NEAR TERM...Lambert/Dangelo
SHORT TERM...Lambert/Dangelo
LONG TERM...Lambert/Fitzgerald
AVIATION...Lambert/Gartner/Colbert