543
FXUS61 KCTP 070303
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1103 PM EDT Mon May 6 2024

.SYNOPSIS...
Central PA will remain in the vicinity of an oscillating frontal
boundary through midweek, with one wave on the front passing north
of the state early Wednesday and another more significant wave of
low pressure passing south of Pennsylvania Thursday. An upper level
trough will then pivot into the region late this week into next
weekend.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Late evening water vapor loop shows a potent-looking shortwave
crossing the Central Appalachians into Western VA. Scattered
convection preceding this feature has diminished with boundary
layer cooling this evening. However, falling heights and a bit
of elevated instability supports a slight chance of showers
overnight across Southern PA.

Meanwhile, a weak cold front is currently located just south of
I-80 and is progged to slide into the southwest corner of the
forecast area by dawn. Breaking clouds and drier air north of
this boundary should allow temperatures to cool to the mid and
upper 40s over the northern tier late tonight. Further south,
more persistent cloud cover and higher humidity will result min
temps between 55-60F over the southern half of the state. Have
added patchy fog to the late night forecast over Southern PA.
Dewpoint depressions are near zero, so it will only take a few
breaks in the overcast to cause fog to form.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
Upper level ridging over PA should result in a dry and warm Tuesday
over most of the forecast area with highs in the low to mid 70s.
However, instability and low level convergence in the vicinity of an
approaching warm front will likely result in scattered PM
showers/tsra over the southwest part of the forecast area. Modest
capes of less than 500 J/kg signal little risk of severe weather.
High pressure and associated low-pwat airmass traversing upstate NY
should provide the northern tier counties with mostly sunny skies
Tuesday. Elsewhere, model RH profiles support a mix of sun and
cumulus.

Tuesday night should be very warm for early May, as the region
breaks into the warm sector south of a weak surface low tracking
across the Eastern Grt Lks. Falling heights and surging low level
moisture ahead of the parent shortwave should support a round of
showers/tsra across most of the region Tuesday night accompanying
the passage of the low level jet. The latest HREF supports POPs from
60-90pct, with the highest POPs across the W Mtns.

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 /03Z TUESDAY THROUGH SATURDAY/...
Conditions remain mainly VFR for much of the central PA
airspace this Monday evening. Only reductions attm are from
showers with a few lightning strikes possible around KAOO for
the next hour or two. Another area of showers sliding
northeastward from SW PA could clip KJST as well.

Conditions should slip back through MVFR to IFR in central and
tonight through the mid morning Tuesday with areas of LIFR in
fog and low cigs possible for 2-4 hours centered on daybreak
Tuesday across the Middle and Lower Susq Valley.

In contrast, high pressure building into northern PA from the
Grt Lks, will push drier air into that part of the state,
keeping conditions mainly VFR there through tonight.

A warm front lifts northeast across western and central PA
Tuesday 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.

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...Fitzgerald
NEAR TERM...Fitzgerald
SHORT TERM...Fitzgerald/Bowen
LONG TERM...Lambert/Fitzgerald
AVIATION...Lambert/Gartner