402
FXUS61 KCTP 090919
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
519 AM EDT Fri May 9 2025

.SYNOPSIS...
*Noticeably cooler end to the week with periods of rain
 pivoting over the southeastern half of the forecast area
*Areas of frost to start Mother`s Day weekend over the western
 Alleghenies; otherwise rain-free and very pleasant conditions
 expected through Monday
*Wet weather returns Tuesday-Wednesday with temperatures
 trending above the historical average through mid May

&&

.NEAR TERM /THROUGH TONIGHT/...
Seasonably strong upper trough/closed 500mb low pivoting over
central PA will result in periods of rain and noticeably cooler
temperatures to close out the week. Initially, stratiform rain
will cover the southeastern half of the CWA and then become
more showery as it shifts into the eastern/northeastern parts
of the forecast area this afternoon into tonight. Modest rain
rates will fall short of 1/3/6 hr FFGs, but forecast totals will
add up to 1-1.25" across the lower Susquehanna Valley - where
it is needed the most based on ongoing D2/severe drought
conditions.

With the exception of the far NW mtns, expect plenty of clouds
today especially over the eastern portion of the area with highs
in the 50-60F range sinking 10 to 20 degrees vs. yesterday.
These max temp readings are also 10 to 20 degrees below daily
climo.

Clouds break and rain comes to an end generally from west to
east tonight. High pressure nosing into western PA should allow
for decent radiational cooling with areas of frost probable
along the Allegheny Front from the Laurel Highlands into the NW
mtns. Based on growing degree day (GDD) calculated thresholds
and regional phenology network leaf and bloom indices, we
activated the growing season for the remainder of the CWA and
issued a frost advy for parts of the western and northern
Alleghenies in coordination with WFOs PBZ and CLE.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
Very pleasant and rain-free weather conditions are expected
through Mother`s Day weekend as Canadian high pressure builds
into the Keystone State. Forecast soundings support lowering
dewpoints in the afternoon (via blend of NBM10th %tile) with
large wedge of very dry/low pwat air setting atop a weak
subsidence inversion. Despite minRH values in the 20-30% range,
seasonal green-up and recent multi day rainfall totals have
effectively ended the Spring fire wx season in central PA.

&&

.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 /09Z FRIDAY THROUGH TUESDAY/...
An extensive shield of light to moderate rain will remain over
about the SE half of PA today associated with an area of sfc
low pressure over Central Virginia that will gradually
strengthen as it moves NE along a stalling sfc front. Visibility
reductions in light to moderate rainfall are expected.

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 early this morning. Bases
will fall through the MVFR range and dip into the IFR Category
for numerous locations this morning, before slowly improving
(but still staying MVFR for the bulk of the airfields Friday
afternoon). Improvement to VFR is expected from west to east
later this afternoon into the overnight hours as high pressure
builds in.

Outlook...
Sat-Mon...Mainly VFR.

Tues...Restrictions likely in -SHRA.

&&

.CLIMATE...
Based on seasonal growing degree day calculated thresholds and
regional phenology network leaf and bloom indices, the National
Weather Service office in State College has activated the growing
season across the Western and Northern Allegheny Mountains in
Central Pennsylvania. The growing season is now active across
all of Central Pennsylvania and NWS State College will issue
frost/freeze headlines as needed.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Frost Advisory from 2 AM to 8 AM EDT Saturday for PAZ004-005-
010-017-024-033.

&&

$$

SYNOPSIS...Steinbugl
NEAR TERM...Steinbugl
SHORT TERM...Steinbugl
LONG TERM...Bowen
AVIATION...Lambert/Banghoff
CLIMATE...Steinbugl