518
FXUS61 KCTP 260258
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1058 PM EDT Sat May 25 2024

.SYNOPSIS...
A shortwave passing north of the region will push a weak cold
front through the state Saturday night. Low pressure will then
track west of Pennsylvania Sunday night into Memorial Day, with
the trailing cold/occluded front coming through Monday evening.
An upper level trough will build into the region for the
remaining portion of next week.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Showers and tsra have exited the forecast area as of 03Z.
Clearing skies, wet ground and a calm wind has led to extensive
valley fog late this evening over Northwest PA. A weak and
diffuse cold front over NW PA will push southeast across the
region tonight. Can`t rule out a lingering late night shower
with the fropa over the southeast part of the forecast area,
where higher pwats and some lingering instability remain.
Otherwise, the rest of the night should be rain-free.

Expect valley fog to become widespread over the entire region
overnight, as skies clear from west to east. Dewpoints don`t
dip much at all. Mins of 60-65F in the SE half and 55-60F in the
NW half are a little milder than normal. Not much wind at all
in the morning, so it may take 2-3hrs after sunrise before all
the fog goes away.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY/...
As the fog lifts on Sunday, another warm day is expected with
highs surging into the upper 70s to middle 80s and ample
sunshine. The front that sweeps through tonight will turn around
and lift northward again Sunday afternoon and usher in more
moisture Sunday night. Scattered thunderstorms will develop
across the southern tier Sunday afternoon south of the front
where MLCAPE may approach 1000 J/kg. Although instability is
rather meager, slow storm motions could result in some localized
flooding in the afternoon and overnight, as reflected in the
MRGL excessive rainfall outlook from WPC.

By Sunday night, a seasonably strong surface low will move northeast
across the Great Lakes, with a trailing cold/occluded front
likely coming through Central PA Monday night. Falling
heights/upper level diffluence ahead of the associated upper
trough, combined with surging pwats along the attendant low
level jet, should result in numerous showers/tsra late Sunday
night through Memorial Day. Ensemble median rainfall during this
time period is 0.50-1.00 inches, representing the most likely
areal averages. However, embedded tsra should result in locally
heavier amounts and potentially an isolated flood threat.

Latest guidance indicates the threat for severe weather on
Monday is worthy of monitoring, especially given that it will
occur on Memorial Day and many outdoor activities/festivals are
planned across the Commonwealth. The Storm Prediction Center has
placed south central PA (areas south/east of I/99 & I-80) in a
Slight Risk for severe weather. An elevated mixed layer is
progged to advect into the region on Monday over top of a
northward advancing warm sector. The result will be MLCAPE
likely in excess of 2000 J/kg for some portion of southern PA
(perhaps as far north as I-80) along with strong mid level flow
and deep layer shear. Model soundings and hodographs (from the
NAM in particular) are supportive of discrete cells with all
hazards possible, including a tornado or two.

In addition to the threat for damaging winds, hail, and a
tornado or two, heavy rain/flash flooding is possible on Monday.
Anomalous PWATs (>97th percentile) will provide ample moisture
in a convective environment supportive of training storms and
perhaps multiple rounds of convection. Ensemble mean rainfall
amounts are generally 0.75" to 1.5" from Sunday night through
Monday night with the majority falling between 8AM and 8PM on
Monday. WPC has drawn a Slight Risk of excessive rainfall in
eastern PA extending from Harrisburg northeast into the
Poconos. In this area they mention the potential for up to 2.5"
of rain in an hour and rainfall totals of up to 5" in areas that
receive multiple rounds of showers.

There remains some uncertainty with the northward extent of the
warm sector, location of heaviest rain, and mode of storms on
Monday. As forecast details come into focus, the most important
takeaway is that those with outdoor plans on Monday should
continue to monitor the forecast and make contingency plans for
moving activities indoors as conditions warrant.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Medium range guidance all points to a period of cool weather
later next week, as a deep upper level trough pivots southeast
from the Grt Lks. The cold temps aloft should support a daily
chance of diurnally-driven showers, with the highest POPs across
the elevated heat source of the Allegheny Plateau. The best
chance of showers and isolated tsra overall should come with
the passage of a strong shortwave Wednesday. Both the GEFS and
EPS signal dry and warmer weather late next week, as the upper
trough shifts east of PA and Canadian High Pressure builds
southeast into the region.

&&

.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
Scattered showers and storms will continue to impact the Susq
Valley (IPT, MDT, LNS) before pulling east of the region late
this evening. Elsewhere, predominantly VFR conds are expected
through late evening.

Overnight into Sunday morning, confidence remains high (60-80%)
that IFR conds in lower ceilings and/or fog will develop over
much of central PA. LAMP guidance has backed off a bit on fog
development across the Lower Susq Valley, but the HREF is
holding onto a 50-70% chc of IFR conds there overnight.

Restrictive conditions are expected to improve by mid to late
morning on Sunday, with VFR conds returning by ~14z in most
spots.

Outside of any thunderstorms this evening, surface winds look
fairly light through the TAF period (generally 5 kt or less).

Outlook...

Monday... Persistent restrictions are expected in widespread
showers and thunderstorms.

Tue-Wed...Brief restrictions are possible in scattered showers,
but much of the time should be VFR.

Thu...Predominantly VFR.

&&

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

&&

$$

SYNOPSIS...Fitzgerald
NEAR TERM...Fitzgerald/Banghoff
SHORT TERM...Banghoff
LONG TERM...Fitzgerald/Banghoff
AVIATION...Evanego