-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KCTP 200316
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1116 PM EDT Fri Apr 19 2024

.SYNOPSIS...
A weak front will push east across the region early tonight,
accompanied by a narrow band of rain showers. Expect cooler
conditions for the weekend with a gusty west to West-northwest
breeze on Saturday. Frost is possible Sunday and Monday
mornings as high pressure moves overhead.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Falling heights, surging pwats and low level convergence along
an occluded front is producing a band of light showers at 00Z
along the spine of the Alleghenies. Some patchy high elevation
fog/drizzle is also likely occurring to the east of the
occluded front, where model sfc-850mb RH fields are near 100pct.

Expect the chance of showers and high elevation fog/drizzle to
shift east overnight, as the occluded front pushes through.
Behind the front, a much drier westerly flow has already arrived
over the NW Mtns and expect this air mass to spread into all but
the Lower Susq Valley by dawn, accompanied by partial clearing.
Min temps at sunrise should vary from around 40F over the NW
Mtns, to the low 50s in the Lower Susq Valley.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Any lingering showers should exit Lancaster Co by around 12Z
Sat, as the front edges east of the region. A good amount of
sunshine is anticipated during the mid morning hours, but
diurnal heating and cold temps aloft should result plenty of
cu/stratocu by afternoon, especially over the N Mtns. There
could even be a sprinkle or two out of any of the deeper cu
that form across the nrn half of the CWA, but not enough to
warrant anything higher than a 10 PoP. Cloud cover and
anomalously cold air aloft should result in high temps several
degrees below average for most of the forecast area. GEFS 2m
temp anomalies indicate the NW Mtns will be most below average,
while the Lower Susq Valley will close to average for late April.

Deep vertical mixing up through 7-8 KFT AGL will tap some 35-40
KT winds, but taking an average of about 70 percent of the max
in the layer yields peak WNW wind gusts of 25 to 30 kts during
the late morning and afternoon hours.

The setup for frost Saturday night is uncertain, depending on
the timing and coverage of low clouds that may develop in a thin
layer of upslope moisture beneath the low level inversion. If
more clouds develop earlier in the night, Saturday night could
be more of an advective marginal cold freeze setup (vs. more
favorable radiational/decoupling frost pattern.) But for now,
models suggest there could be at least a few hours of mostly
clear skies and light winds before the clouds develop, during
which frost can form. Low temps are fcst in the 30-35F range
over the northwest half of the CWA which could impact counties
activating the growing season April 21 along the US220/I99/I80
corridor.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
-- Changed Discussion --
Model guidance all supports dry conditions Sunday through
through Tuesday morning, as high pressure and an associated
low-pwat air mass builds into the area. However, upper level
troughing does support below average temperatures into early
next week.

The combination of light winds, dry air, and mostly clear skies
associated with surface ridging is likely to result in good
chance of frost Sunday night. The greatest risk of frost is
over the northern mountains where the growing season is not
active, but areas in the growing season further south could also
be affected.

A decent warmup looks likely Tuesday, as high pressure passes
off of the east coast. However, medium range guidance all points
to a chance of showers and a subsequent cool down associated
with a cold front passage Tuesday night into Wed AM. The
moisture return ahead of the front looks unimpressive, but
strong forcing ahead of a potent upper level shortwave suggests
a good chance of rain. Latest plumes support a general 0.2 to
0.4 inch rainfall.

It appears there will be another chance of a frost/freeze Thu
and Fri AM, as Canadian High Pressure builds over the region.
Those with agricultural interests should keep an eye on the
forecast for the end of next week.
-- End Changed Discussion --

&&

.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
Widespread MVFR cigs through the early evening hours with some
patches of IFR cigs near and and along a broken line of SHRA.
These showers will continue to move eastward bringing brief
periods of low-end MVFR to high-end IFR cigs to all airfields
outside of JST/BFD. Later this evening, expect VFR conds to
develop throughout much of western PA with restrictions
remaining across the eastern airfields with low/moderate
(30-40%) confidence. The main source of uncertainty is the
potential for lingering showers to remain at MDT/LNS (lesser
IPT) and keep restrictions down into the 07-09Z timeframe.

In the wake of this broken SHRA, expect quick improvement at
all airfields with VFR expected to prevail through 00Z Sunday,
as observed in recent obs at DUJ/LBE. The main concern after
sunrise Saturday will be a gusty WNW (270-310) wind with
sustained winds 15-20 kts, gusting up towards 30kts developing
for the late morning and afternoon hours and continuing into the
early evening hours.

Outlook...

Sun-Mon...No sig wx expected.

Tue...Slight chance of evening showers/cig reductions NW Mtns.

Wed...Showers move in west-to-east from rain early, continues
throughout the day. TSRA possible SW late PM.

&&

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

&&

$$

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