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000
FXUS61 KCTP 210005
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
805 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/...
Monday looks to be dry but still colder than normal. With
light winds and dry air in place, still looking at potential
for more frost Monday night. Models show 850 mb temperatures
over Hudson Bay at times as cold as 24 degrees below at 850 mb.
Central PA nothing that cold, but did see some snow flakes at
times earlier this afternoon at JHW. I think the calender
reads late April, but mother nature making up for the all the
mild weather we had this winter and spring season so far.

Good timing between models with more showers moving into the
area around 00Z Wednesday. Showers likely to be largely out
of the area by late Wednesday evening.

While dry weather is expected Thursday into Friday, as high
pressure builds into the area, there will be potential for
frost again on Thursday night.

Temperatures will moderate by next weekend, but there will be
a chance of some showers. EC has more upper level ridging across
our area next weekend, which would support drier and warmer
conditions than the GFS would support.

&&

.AVIATION /00Z 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 from 2 AM to 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...Martin
AVIATION...NPB