617
FXUS61 KCTP 252116
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
516 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/...
Isolated thunderstorms have continued to fire across the warm
sector ahead of showers associated with the surface trough in
western PA this afternoon. Despite 1000+ J/kg of mixed layer
CAPE, weak deep layer shear (<30kts) has capped storm intensity
thus far with only small hail and sub-severe winds. Scattered
storms will continue to cycle in southeast PA this evening with
more widespread showers and embedded thunderstorms along the
surface trough in their wake. Storms in western PA have had a
history of producing wind gusts near severe criteria and will
need to be watched as they move into an environment with DCAPE
of around 800 J/kg.

In addition to wind and small hail, localized flooding is
possible tonight. A few locations have picked up >2" of rain so
far based on radar estimates (Blair/Huntingdon border and
eastern Juniata County). Any flooding should be isolated in
nature due to the progressive nature of storms. Hi- resolution
guidance brings the line of showers to AOO/UNV/IPT by 6 or 7PM
and southeast of I-80 by 9 or 10PM.

After showers exit the region overnight, drier air will move in as
a cold front pushes across. The front will likely be behind the
forcing and not make more than an isold SHRA or two as it
passes. Have kept PoPs below mentionable for the second half of
the night. The clearing and rain today will likely lead to fog
forming over a good portion of the CWA tonight. 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 drier and warmer weather late next week, as the upper
trough shifts east of PA.

&&

.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
18z update... Outside of brief restrictions in thunderstorms
this afternoon and early evening, mainly VFR conditions are
foreseen through much of this evening (02-04z). If restrictions
do develop with passing thunderstorms, it is expected to last
for 30 minutes or less.

Later tonight into early Sunday, confidence remains high
(60-80%) that lower ceilings and fog will develop over most of
central PA. IFR to low IFR conditions appear to be most likely
between 08z and 12z.

Early indications are that restrictive conditions will improve
fairly quickly Sunday morning, with VFR returning by 14-15z.
Confidence in this timing is moderately high (50-70%).

Surface winds look fairly light through the period (generally 5
kt or less). The one exception could be in or near any
thunderstorms, where brief gusts of 20-30 kt would be possible.

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 could well end up in VFR status.

&&

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

&&

$$

SYNOPSIS...Fitzgerald
NEAR TERM...Banghoff
SHORT TERM...Banghoff
LONG TERM...Fitzgerald/Banghoff
AVIATION...Jurewicz/NPB