708
FXUS61 KCTP 201545
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1145 AM EDT Sat Jul 20 2024

.SYNOPSIS...
*More humid start to the weekend with a couple of thundershowers
*Trending hotter but rain-free and less humid end to the weekend
*Seasonably warm with daily opportunities for much-needed rain
 next week

&&

.NEAR TERM /THROUGH TONIGHT/...
950AM/1350Z: Radar trends this morning show a couple of showers
developing near or just to the southeast of a subtle low level
convergence/moisture boundary located roughly from KJST->KN37.
Latest model guidance show sct convection continuing to expand
along and to the southeast of this boundary through the
afternoon with a couple of thundershowers/downpours most likely
over the southeastern 1/2 of central PA through the evening.
Partly to mostly cloudy skies today with highs near late July
climo in the 80-85F range. Expect more noticeable/sticky
humidity with dewpoints 60-65F to the east of the Allegheny
Front. Not everyone will get wet today and it won`t be raining
all the time with max POP 50-60%. Showers and a few t-storms
could linger and be slow to dissipate/shift to the east tonight
as indicated by the latest hires ensemble mean/NBM precip fields.

Previous Discussion Issued: 540 AM EDT Sat Jul 20 2024

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 TUESDAY/...
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.

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.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
An upper-level trough axis will remain centered over the Great
Lakes Wed into Thurs, with unsettled weather continuing for
central PA under a continued chc of (mainly aftn/eve)
SHRA/TSRA. Southwesterly flow at the sfc and aloft will keep us
warm and humid as well.

The trough axis should finally swing through by the end of the
week, accompanied by a cold frontal passage, which should bring
a decrease in PoPs Friday into next weekend. Temperatures look
to remain seasonably warm, although humidity should come down
following the passage of the front.

&&

.AVIATION /16Z SATURDAY THROUGH WEDNESDAY/...
At 15z, considerable high and mid-level cloudiness is
overspreading all but far northwestern PA and some cu is
beginning to pop up. There is a patch of SHRA (and even a bit
of thunder) over the southern Alleghenies (SW of KAOO).

Expect scattered showers (and isolated thunder) to continue to
pop up with the heat of the day, primarily along and southeast
of I-99. Outside of any SHRA/TSRA, VFR conds should prevail.

Skies should clear out later this evening into the overnight
hours, and winds will diminish. This could aid in the formation
of some fog, especially in areas that receive rainfall today.
Have not hit the fog hard at any TAF sites yet, but have hints
of it at several locations.

Sunday should feature predominantly VFR conds, once any fog
burns off in the AM.

Outlook...

Mon-Wed...Patchy early morning fog possible. Otherwise,
scattered (mainly aftn/eve) SHRA/TSRA developing with brief
restrictions possible.

&&

.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).

The average temperature from June 1 to July 19 at Harrisburg is
78.1F which is the warmest summer-to-date on record.

The average temperature from January 1 to July 19 at Harrisburg
is 55.6F which is the warmest year-to-date on record.

&&

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

&&

$$

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