270
FXUS61 KCTP 200614
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
214 AM EDT Sat Jul 20 2024

.SYNOPSIS...
An upstream shortwave over the Lower Mississippi Valley will
track northeast across Pennsylvania late Saturday. High pressure
will build into the state behind this feature Sunday, then an
advancing warm front will stall out in the vicinity of
Pennsylvania for much of next week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Late evening satellite imagery shows clear skies across Northern
PA, where a high pressure ridge and low-pwat air resides. Some
of the coolest mesonet observations in this area have already
dipped into the upper 50s as of 02Z. Further south, sct-bkn
cumulus are noted over Southern PA, associated with low level
moisture advection and modest height falls ahead of an upstream
shortwave over the Miss Valley. Can`t rule out an isolated late
night shower across the southwest part of the forecast area, as
large scale forcing increases ahead of this feature.

Efficient radiational cooling and warm water temps will likely
result in late night fog in the deep river/stream valleys of
Northern PA. Elsewhere, increasing cloud cover should limit the
fog potential, despite increasing low level moisture. Morning
lows on Saturday should range from around 50F in the coolest
valleys of the NW Mtns, to the upper 60s across the Lower Susq
Valley.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/...
The focus Saturday will be on the upstream shortwave, which is
progged to lift northeast across the Central Appalachians late
in the day, then pass over Central PA during the evening. Model
RH profiles indicate warm advection aloft ahead of the shortwave
will spread of veil of cirrus across all but perhaps the
extreme northwest part of the forecast area, which will limit
diurnal heating. However, a southerly flow and associated low
level moisture advection, combined favorable large scale forcing
beneath the right jet entrance region, should support scattered
convection by afternoon. The focus of the showers and isolated
tsra should be in the vicinity of a weak surface trough running
along the spine of the Appalachians from Somerset County
northeast to Sullivan County.

Latest ensemble output suggest most places will receive less
than a tenth of an inch, with isolated pockets exceeding 0.5
inches possible. Weak shear and very modest instability will
almost certainly preclude any severe weather or flooding
concerns Saturday.

Passage of the shortwave should result in any showers ending by
late evening over the northeast part of the forecast area. High
pressure building into the state behind the shortwave should
bring clearing skies and light winds late Sat night. Latest
SREF/NAMNest indicate the likelihood of patchy late night valley
fog, mainly in the favored deep river/stream valleys of the
Alleghenies, but also in any spots the receive rain Sat PM.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Fair and warm weather with light wind and moderate humidity
is expected Sunday, as surface ridging and associated low-pwat
airmass builds across the state. Ensemble mean 850mb temps near
17C supports max temps ranging from the low 80s over the N
Mtns, to around 90F across the Susq Valley.

Medium range guidance all point to a showery period with high
humidity and more clouds than sun for much of next week, as an
advancing warm front stalls out in the vicinity of PA. The 500mb
pattern features upper ridging off of the East Coast and a
persistent trough over the Grt Lks. A deep southwest flow at the
interface of these features will import GOMEX moisture
northward, interacting with the front to promote multiple days
of diurnally enhanced showers/thunderstorms and potentially
beneficial rainfall. The southern tier of central PA could
really use some rain to lessen the impacts of moderate to severe
drought conditions (D1-D2 drought monitor).

Ensemble plumes indicate highs Monday will be several degrees
above average with only a limited chance of PM convection across
primarily Southern PA. After that, plenty of cloud cover and
more numerous showers/tsra should hold daytime temps to near
seasonal norms. Surging pwats along the frontal boundary should
translate to very warm/muggy nights.

Model guidance begins to diverge toward the end of the forecast
period with some models tracking the upstream trough north of
PA, which pushes the front south of the area and introduces
drier weather by Friday. However, the latest GEFS/EPS look a bit
less progressive, suggesting the fropa and return to drier
weather takes until Saturday.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
High cirrus will be on the increase overnight as an upper level
disturbance moves north out of the southern Appalachians.
Most airfields will remain VFR through the night, although
patchy valley fog is expected once again in the northern
valleys. There is some signal for MVFR cigs at BFD closer to
sunrise (after 10Z), thus have shown some deterioration in this
timeframe with low-end MVFR to high-end IFR vsbys in the
10Z-12Z Saturday timeframe with moderate (50-60%) confidence.

Scattered rain showers and potentially a few areas of
stratiform light rain will develop early Saturday and continue
throughout the afternoon and evening hours mainly east of
BFD/JST. A few thunderstorms are possible as well, but low CAPE
will be a limiting factor. After SHRA tapers off, winds are
expected to become light with clearing skies potentially
allowing for fog formation Saturday night into Sunday morning.

Outlook...

Sun...Primarily VFR. Patchy late night/early morning fog and
low ceilings are possible.

Mon...Primarily VFR. Patchy early morning fog possible.
Scattered afternoon SHRA/TSRA.

Tue-Wed...More widespread PM SHRA/TSRA could lead to at least
brief restrictions.

&&

.CLIMATE...
The average temperature from July 1 to July 18 at Harrisburg is
81.6F which is the warmest July month-to-date.

&&

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

&&

$$

SYNOPSIS...Fitzgerald
NEAR TERM...Fitzgerald
SHORT TERM...Fitzgerald
LONG TERM...Fitzgerald/Steinbugl
AVIATION...Colbert/NPB
CLIMATE...Steinbugl