NWS Forecast Discussion
233
FXUS61 KCTP 090350
AFDCTP
Area Forecast Discussion
National Weather Service State College PA
1150 PM EDT Thu May 8 2025
.SYNOPSIS...
*Cooler with periods of rain overnight across the SE half of the
state, gradually pivoting to cover mainly the eastern third of
PA by Friday night
*A pleasant weekend is on tap, with drier and seasonable
conditions Saturday and Sunday
&&
.NEAR TERM /THROUGH FRIDAY/...
Surface cold front has slowly pushed to the southern border of
PA along and to the east of I-81, and into the MD panhandle and
WVA further to the west.
The approach of better large scale UVVEL beneath the right
entrance region of an upper jet and deepening upper
trough/closed low over the Lower Glakes will gradually
strengthen a surface low (currently 1012 b over Central VA) as
it rides NE along the boundary overnight and Friday.
Elevated, slightly negative LIs (0 to -1C) in the 925-850 mb
layer across the far SE zones this evening will support some
low-topped convection and a few more hours of briefly heavy
rainfall rates, with a transition to a cooler, stratiform rain
after midnight. Additional rainfall totals overnight/Friday will
average between 0.25 and 0.30 near and just SE of a KAOO to KIPT
line with a little over an inch likely across the region SE
of I-81.
For our far NW zones, little to no rain will fall through
Friday except for some isolated to scattered showers at the pool
of coldest low to mid level air moves overhead.
Min temps tonight will display a pretty hefty gradient from NW
to SE, ranging from the upper 30s across the NW Mtns to the low
to mid 50s in Lancaster Cty (and around 60F in the Greater
Philly area.
&&
.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
A slow moving and nearly stacked low pressure wave near the
Delmarva coast will be our main controlling feature Friday into
Friday evening. This system will continue to bring light-
moderate rain, mainly for areas near and east of US-15, as well
as south of I-78/US-22. The back edge of the steadier rain
shield is expected to slowly drift towards the east, with an
anticipation that much of the afternoon could end up rain-free
for areas west of a Williamsport-State College- Altoona line.
Given thicker clouds, rain, and a cooler, maritime type air
mass, afternoon highs will be stuck in the upper 50s-lower 60s
for most.
By later Friday night, much of the rain should push east of PA,
with at least partial clearing likely to develop, particularly
farther west near the Allegheny plateau. Any areas that clear
out Friday night could well see at least patchy fog, given damp
ground conditions and light winds.
A substantial improving trend in the weather is still expected
this weekend, as the aforementioned rain-making system tracks
well offshore, with a large high pressure ridge expanding into
the Commonwealth from eastern Canada. This pattern evolution
should bring clearing skies to all on Saturday, with a sunny,
pleasant Mother`s Day, featuring seasonable high temperatures in
the upper 60s and 70s.
&&
.LONG TERM /MONDAY THROUGH THURSDAY/...
Medium range models shows quite a remarkably symmetrical rex
block Sunday night with its axis extending just west of the Miss
River (and SW and SE US coast ridges connecting with the 500 mb
positive anomaly over Minnesota).
This pattern will break down on Monday, allowing the fairly
deep cutoff low over the gulf coast to lift NE and carry
abundant Gulf Moisture for a Tuesday to Wednesday rain event.
Models do show some slight timing differences in this feature,
but all do show the same basic evolution of this breakdown to
the stable upper level pattern that will bring us a 3 day string
of dry, pleasant weather for the upcoming Mother`s Day weekend.
Previous Disc...
Monday will mark the last day in a stretch of dry days over
Mother`s day weekend. High pressure ridging will be present over
much of the Mid-Atlantic region, and max temperatures for the
beginning of the extended period will be in the low to mid 70s
across all of Central PA. However, another upper level closed
low progged to approach up the Mississippi and Ohio Valleys on
Tuesday signals the return of a multi day unsettled pattern for
the region.
The chance for scattered showers (or even periods of steady
light to moderate rain) increases starting on Tuesday with
south easterly upper-level flow expected ahead of the low
providing ample moisture from the Atlantic Coast. Confidence
decreases in the spacial extent of precipitation as the long
range models have significant differences in how they resolve
this closed low. The deterministic ECMWF holds onto a blocking
type pattern with a deep trough over the Commonwealth, similar
to what occurred this past week, while the GFS shows more
progression into zonal flow over Central PA. Given the spread in
guidance we`re choosing to lean on the side of being unsettled
and stormy towards the middle and end of next week.
&&
.AVIATION /04Z FRIDAY THROUGH TUESDAY/...
Showers (and even a few low-topped TSRA near and to the south of
a KTHV to KLNS line early tonight) will evolve into a more
extensive shield of light to moderate rain over about the SE
half of PA late tonight and Friday as an area of sfc low
pressure over Central Virginia gradually strengthens as it moves
NE along a stalling sfc front.
A 5-10 kt north to northeast flow across Central PA and the Susq
Valley will transport cooler/moist air into the region and lead
to gradually lowering cloud bases overnight and Fri AM. Bases
will fall through the MVFR range and dip into the IFR Category
for numerous locations Friday morning, before slowly improving
(but still staying MVFR for the bulk of the airfields Friday
afternoon).
Later tonight and Friday morning, there is high confidence
(80-90%) in the development of widespread lower clouds and rain.
Ultimately, fuel alternate-IFR restrictions are anticipated.
Any improvement Fri afternoon would favor the western terminal
sites (KBFD and KJST), but this won`t take place until after
18z.
Outlook...
Sat-Mon...Mainly VFR.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Jurewicz/Lambert
NEAR TERM...Jurewicz/Lambert
SHORT TERM...Jurewicz/Lambert
LONG TERM...Bowen
AVIATION...Jurewicz/Lambert
NWS CTP Office Area Forecast Discussion
