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FXUS61 KCTP 201115
AFDCTP

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

.SYNOPSIS...
An upstream shortwave over the Lower Mississippi Valley will
track northeast across Pennsylvania later today. 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 /THROUGH TONIGHT/...
Efficient radiational cooling and warm water temps have
resulted in fog in the deep river/stream valleys of Northern PA
this morning. Farther south, increasing clouds have kept
temperatures a bit warmer as dewpoints slowly creep up. A small
batch of rain showers will move northeastward through the Lower
Susquehanna Valley over the next few hours and exit east by 9
or 10am.

The main focus for today`s weather will be a shortwave that 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 continue to 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.

&&

.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
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. Latest HREF
indicates a mix of sun and clouds on Sunday afternoon with some
fair weather cumulus and a broken deck of cirrus.

Clouds will continue to thicken up overnight Sunday night as
low temperatures continue their slow upward trend. Lows by
Monday morning will be ~5 degrees above normal for this time of
year, ranging from the upper 50s in the north to low 70s across
the southeast. By daybreak Monday, showers should be on our
doorstep ahead of an approaching warm front.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
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 that plenty of cloud cover and more
numerous showers/tsra should hold daytime temps to near seasonal
norms Monday through the upcoming week. 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 /12Z SATURDAY THROUGH WEDNESDAY/...
Higher clouds across central PA this morning will gradually
thicken as the day progresses as a disturbance continues to move
northeastward across the Alleghenies. Generally, VFR conds are
expected throughout the day with the main concern being showers
and isolated thunderstorms mainly along JST/AOO/UNV/IPT and the
LSV (MDT/LNS). At this time, highest confidence at JST/UNV/IPT
of precipitation and have timed out the best timing in the 12Z
TAF package. TSRA will mainly be isolated, but have outlined
VCTS at IPT where slightly more instability could allow for a
thunderstorm between 20Z-23Z Saturday.

Skies are expected to clear out later this evening into the
overnight period and could lead to localized fog formation in
areas that receive rainfall today. At this time, confidence is
low as there could also be some thinner mid-to-high level clouds
lingering overnight that could also limit fog formation. The
highest probabilities of restrictions are outlined at IPT where
there is a higher chance of showers and clearing but have
limited any restrictions slightly above MVFR thresholds at this
time due to low confidence.

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 19 at Harrisburg is
81.2F which is the 4th warmest month-to-date on record (81.3F
in 1966, 2012, and 2020).

&&

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

&&

$$

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