756
FXUS61 KCTP 200217
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1017 PM EDT Fri Jul 19 2024

.SYNOPSIS...
* High pressure over the region will maintain dry weather and
  lower humidity into early Saturday.
* Southerly winds usher in an uptick in humidity on Saturday
  with scattered afternoon showers and thunderstorms.
* Dry conditions on Sunday into Monday precede a more unsettled
  pattern next week with seasonable temperatures.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY 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 SATURDAY MORNING THROUGH SATURDAY NIGHT/...
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 THROUGH FRIDAY/...
Temperatures will trend a few degrees above normal Sunday
afternoon as high temps across the south approach 90 once again.
Dry weather continues Sunday night as clouds continue to stream
in and humidity increases. The uptick and clouds and humidity
will help overnight lows continue to moderate each day into next
week.

Near to below normal pwats beneath a weak area of high pressure
will provide a rain-free and less humid end to second-to-last
weekend of July. There should also be good viewing at night for
the full Thunder or Buck moon with patchy fog developing in the
northern river/stream valleys into early Monday morning.

Latest model and ensemble guidance shows an amplified pattern
that will be fairly slow to evolve next week. The key synoptic
features will be a wavy front on the leading edge of a Great
Lakes to southern Plains mean trough that will promote multiple
days of diurnally enhanced thunderstorms and potential heavy
rainfall across the region. 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).

Max/min temperatures (80-90/60-70F) will remain above the
historical average with for late July with humidity/dewpoints
returning to elevated levels; however the heat and humidity
combination is not expected to be excessive.

WPC introduced a marginal risk ERO for day 5/Tuesday with
guidance ramping pwats to 1.5-2.0 inches or +1-2SD. The Tuesday
into Wednesday timeframe appears to have the best odds for
heavy rainfall (max POPs) before pwats trend lower from NW to
SE as the frontal zone slowly presses to the southeast with
time by late week.

&&

.AVIATION /02Z 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. Opted not to include vsby restrictions at BFD in the
00z TAF package and instead went with VCFG, but the LAMP does
still show nearly a 50 percent chance of IFR or lower vsby at
BFD late tonight into early Sat morning.

Midlevel clouds will thicken after 12z Sat, with scattered rain
showers and potentially a few areas of stratiform light rain
developing. A few thunderstorms are possible as well, but low
CAPE will be a limiting factor. Most airfields will remain VFR
through the TAF period.

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...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...Lambert/Banghoff
NEAR TERM...Fitzgerald
SHORT TERM...Fitzgerald
LONG TERM...Steinbugl
AVIATION...Colbert
CLIMATE...Steinbugl