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000
FXUS61 KCTP 210323
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1123 PM EDT Sat Apr 20 2024

.SYNOPSIS...
An upper level trough with unseasonably cold air aloft will
swing through eastern Canada and the northeastern states late
this weekend. Frost is expected in many areas of Central and
Northern PA Sunday morning, and may be even more likely on
Monday morning as high pressure moves overhead and the sky
clears. Monday night will be on the cold side still.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Clearing skies, a diminishing wind and anomalously low pwats
will set the stage for efficient radiational cooling tonight,
with temperatures 5-10 degrees below average. Have trended below
NBM min temps due to the nearly ideal conditions for rad
cooling, with expected lows ranging from the mid 20s in the
coldest northern valleys, to the upper 30s in the more urbanized
parts of the Lower Susq Valley. A frost advisory remains in
effect for those counties in the active growing season, where
widespread frost is expected. Patchy frost appears likely even
in the normally colder rural parts of the Lower Susq Valley.

Playing this early season frost on the cautious side, since
we`ve bumped up the start of the official growing season by
about 10 days across much of the SE half of the CWA and have
received calls concerned about the frost. That being said, the
negating factor for potentially more widespread frost is a layer
of thickening Cirrus/Cirrostratus that will drift across much
of Southern PA late tonight. Across the NW Mtns, expect
increasing stratocu late tonight associated with cooling temps
aloft ahead of an approaching shortwave.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
Dry weather and relatively light winds are expected Sunday
associated with surface ridging over the area. However, upper
level troughing will result in a cool day for late April
standards, with highs ranging from the upper 40s over the higher
elevations of the Alleghenies, to the mid to upper 50s in the
Lower Susq Valley.

Warm advection aloft preceding the trough will likely result a
good deal of cirrus across Southern PA through early afternoon,
and cold temps aloft should result in a fair amount of cumulus
across the north. Brightening skies are likely by late
afternoon, as a shortwave passes east of PA. Can`t rule out a
light shower/sprinkle over the N Mtns, where low level
instability is greatest. However, in general, boundary layer
moisture should be too dry for any showers Sunday.

Clearing and chilly conditions are expected Sunday night, as the
upper trough and associated cloudiness depart. Surface ridging
and dry air will again result in efficient radiational cooling,
with lows in the low to mid 30s for most of the region with
areas of frost.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Model guidance all supports dry conditions Monday through
through most of Tuesday, 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 Monday night across the central and
northern counties.

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.

The next chance of rain will come Friday night into Saturday
associated with low pressure lifting into the Grt Lks and the
associated warm front approaching PA.

&&

.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
VFR conds are expected to continue through 00Z Monday with high
(> 90%) confidence. Some SCT low-level clouds (5000-8000ft AGL)
will continue for the next couple of hours across NW PA before
giving way to SKC conditions. Some low-level clouds are expected
to return during the morning/early afternoon hours on Sunday
with ceilings above 5000ft AGL expected.

Winds will slowly be on the decrease overnight at 300-340 with
recent observations outlining some gusts up to 20-25kts across
SE PA. Winds are expected to dip below 10kts sustained by 2Z
Sunday and continue into the early afternoon hours. Later in the
TAF period, there is moderate (50-60%) confidence in gusts
between 15-20kts at 280-320 after 18Z Sunday at all airfields
outside of MDT/LNS.

Outlook...

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.

Thu...Clearing as high pressure builds into the area.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Frost Advisory until 8 AM EDT Sunday for PAZ019-025>028-034-
035-045-046-049>053-056-057.

&&

$$

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