245
FXUS61 KCTP 230240
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1040 PM EDT Thu May 22 2025

.SYNOPSIS...
* Slow moving upper level low pressure over the Great Lakes and
  NE US will continue our cool and wet stretch of weather with
  frequent showers late today through tonight, before the
  showers become more scattered on Friday.
* Daytime temperatures will be 10 to 20 degrees below the
  historical average through Saturday with no signs of a
  summertime warmup on the horizon
* Slight warming with lowest chance of rain Sunday & Monday
* Cool/wet pattern returns next week

&&

.NEAR TERM /UNTIL 7 AM FRIDAY MORNING/...
The 1004 mb sfc low is currently centered over Lake Ontario and
has been very slowly moving northeastward throughout the day
today. This low along with the upper level trough has seen
additional spokes of energy aloft rotate south and east helping
to elongate and deepen the -2 to -3 sigma 500 mb low/heights over
the Glakes and Mid Atlantic region. The resulting occlusion is
now draped over eastern Pennsylvania down through the
Chesapeake Bay.

The main precip area for tonight will become confined to the
Susq Valley and points east, then primarily the north central
mountains tonight, typical of the late stages of a Miller-B low
pushing through our area with the gradual transfer of energy to
a slowly deepening 1000 mb sfc low near Cape Cod by 06Z Friday.

The deep moisture from today has already to become more shallow
as dry air begins to encroach near 800 mb and above. This has
caused a noticeable decrease in shower coverage across much of
central PA from this afternoon. This and a more Westerly
boundary layer flow will lead to decreasing coverage of showers
over the SW half of the state late tonight into Friday. The
latest HREF ensemble depicts this dry slot in mid levels to
persist through 18Z Friday.

Additional rainfall from this evening through dusk Friday will
range from only around 0.10 of an inch across the south central
Counties of PA to around 0.35 of an inch across the best upslope
areas in Western Somerset County and across the Susq Valley and
locations to the east. Hydro concerns continue to be pretty
much nil as rainfall rates will be mainly 0.10 of an inch per
hour or less through this evening before decreasing late
tonight.

&&

.SHORT TERM /7 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
Pinwheeling double-barrell sfc lows, eventually consolidating
along the Maine Coast Friday afternoon beneath a large scale
cyclonic upper flow/trough will maintain the cool and somewhat
wet pattern for both Friday and Saturday. As is typical with the
upper low passing just to the north of the region and a well
aligned WNW boundary layer flow, most of the SHRA will occur
over the Northern Mtns and Laurel Highlands, with lower chcs to
the SE.

Despite the persistent upper trough, notable drying of the mid
and upper levels (lowering PWATs and sfc Td) and the gradual
shift eastward of the system should diminish the
coverage/frequency of the SHRA. That being said, cool temps
aloft will still support scattered showers, cloudy conditions,
and even some wind gusts approaching 30 mph along the Allegany
front. We may see some improvement in southeast PA by Saturday
afternoon with a few breaks in the clouds thanks to downsloping
northwest flow, but cool temps and mostly cloudy skies are a
good bet for the majority of the area for the majority of the
short term period.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Best chance for a dry day will be Memorial day and perhaps most
of Tuesday.

Similar pattern to what we had yesterday (Wednesday) sets up by
next Wednesday again. Another sfc low stalls over SW Ontario,
as a coastal low reforms off the VA coast. No real sign of the
pattern changing. Some model variation to where the upper level
trough is by next Saturday, which would determine how far west
the area of rain lingers. Cooler than normal temperatures
expected again. A very amplified pattern for late May.

More information below.

If you squint really hard at the upper air charts for Sunday,
you might be able to convince yourself that upper level flow is
becoming slightly less trough-y, but that`s probably just
wishful thinking. We are growing less optimistic to see any
marked improvement before Monday. The recent blocking pattern
has proven to be rather persistent and in no hurry to unravel.
The cyclonic flow and cool temps aloft should translate into a
good deal of cloud cover with POPs peaking during the afternoon
hours coincident with diurnal heating.

Precip probs should bottom on Monday before ramping higher into
Tuesday-Wednesday. Models are coming into better agreement in
tracking the southern stream wave farther to the north. There
are even signs that the briefly split-stream flow will try to
close off into another upper low in the Great Lakes/Ohio Valley
region by the middle of next week. So it appears the cool and
wet pattern will continue into the end of the month with no
signs of summer weather on the horizon (meteorological summer
begins on June 1).

&&

.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
Late evening update.

Not much left on the radar. Adjusted the TAFS some.

Earlier discussion below.

For the 00Z TAF package, looking at mainly low CIGS into
Friday Morning. Visibilities will be low at times with fog
and scattered showers.

For Friday afternoon, expect CIGS to become VFR across
most of the area, but still MVFR across the higher sites
like BFD and JST. Dry air will help improve conditions.

Still a chance of a shower Saturday into Sunday, as weak
systems rotate around a deep upper level low. Best chc
for dry weather will be Memorial Day.

More detail below.

MVFR CIGS will persist through dusk at most other TAF sites then
lower to IFR and LIFR as we head through the middle of tonight
and early Friday.

IFR to MVFR cigs with numerous -SHRA will persist across the NW
Mtns and Laurel Highlands on Friday while a gradual mid to late
morning improvement to higher end MVFR and VFR will take place
across the SE half of the CWA where the best downslope component
will be found.

Outlook...

Sat-Sun...Still a chance of a shower.

Mon...Dry with VFR conditions.

Tue...Widespread showers expected again.

&&

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

&&

$$

SYNOPSIS...Lambert/Dangelo
NEAR TERM...Dangelo/Bowen
SHORT TERM...Dangelo/Bowen
LONG TERM...Lambert/Martin
AVIATION...Lambert/Martin