Irving, Pennsylvania Weather Forecast Discussion

866
FXUS61 KCTP 180919
AFDCTP
Area Forecast Discussion
National Weather Service State College PA
519 AM EDT Thu Sep 18 2025
.SYNOPSIS...
* Areas of Dense Valley Fog expected (primarily across portions
  of Scent and NW PA) through the Morning Commute to work and
  school today.
* High pressure and dry weather builds in for today and Friday.
* Still dry, but slightly cooler with a refreshing fall-like
  airmass highlighted by low daytime humidity this weekend
  before temperatures trend above average next week - not much
  rain in sight.
&&
.NEAR TERM /THROUGH TONIGHT/...
A slowly weakening area of low pressure was located about 100 NM
east of KACY with mid level low pressure following close behind
just to its south. These weather features will continue to drift
ENE and away from our region today.
A ridge of high pressure will build into the region today as
the thermally indirect cell and subsiding branch beneath the
right exit region of a nwrly mid level jet approaches from the
Glakes.
Lingering stratus/stratocu clouds across southeast PA will
gradually erode from North to South by late this morning.
Further west, across Scent PA where skies cleared and sfc
dewpoints were in the upper 50s, we`re seeing dense fog form in
the valleys. A Dense Fog Advisory was recently issued for this
area, along with Warren and Mckean counties in NW PA.
Elsewhere, lower sfc dewpoints and still a 1-2 deg F T/Td
spread in many locations was keeping vsbys at P6SM and the
window for fog formation will be in 11-12Z time period and more
localized.
Lows around sunrise today will vary from the mid 40s across the
north to the low 60s across the Lower Susq Valley where bkn-ovc
sky conditions and dewpoints in the low 60s persisted.
It will take a little while for the moisture in southeast PA to
be replaced by a drier airmass, so expect the air to still feel
a bit humid today.
For the daylight hours today, expect mostly sunny conditions,
light wind this morning and a 5-8 kts WNW breeze breeze with
minor gusts into the low teens this afternoon.
High temps today will range from the upper 70s to around 80 at
elevations above 1500 ft MSL, to the lower and mid 80s in the
valleys of Central and Southern PA.
&&
.SHORT TERM /FRIDAY/...
Friday will be a continuation of what we`ve seen for a majority
of the past couple weeks with plenty of sunshine, seasonably
mild temperatures, and light winds.
Highs will be slightly cooler than Thursday across the north
Friday (in the wake of a weak secondary/backdoor cold front
drifting down from the north), while maxes in the south will be
1-3F higher.
There will be an increase in cloud cover north of US-6 Friday
and this will be the only noteworthy aspect of its arrival.
Even drier air awaits in its wake...
&&
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Friday night - the aforementioned backdoor cold front will
slide through Pennsylvania with a strong 1028mb high surging in
behind it. Dewpoints will plummet by Saturday morning,
supporting a return to below-normal overnight temperatures with
clear skies and calm winds. Surface high pressure will set up
off the New England Coast for the weekend, ensuring moist
southeast flow and tranquil weather. Highs will tick down a few
degrees for the weekend, with highs in the 70s and lows in the
50s most likely at this time.
Heading into next week, high pressure will begin to lose its
grip on the region as an upper trough tries to disrupt the
persistent ridge of high pressure aloft. Still plenty of
uncertainty on how much, if any, precipitation will get into
Pennsylvania, but southerly flow ahead of the approaching
system will support continued warmer than average temperatures
for the start of Astronomical fall.
&&
.AVIATION /08Z THURSDAY THROUGH MONDAY/...
Conditions slowly improving over the southeast with only a
isolated patch of -DZ here and there. Did leave a MVFR to slowly
improving VFR at KMDT and KLNS as the low pressure system exits
to the east.
Slightly more cloud cover this evening could limit earlier fog
projections, with recent RAP/GLAMP guidance scaling back on fog
mentions overnight. The western terminals (BFD/JST/AOO) will
have the highest chances of clear conditions overnight, which
will allow for some formations; however, this looks more limited
to valley locations at this time. Have progged IFR/LIFR
restrictions at AOO based on recent GLAMP/HREF probabilities
with moderate (50-60%) confidence; however, lower confidence
(20-30%) at BFD/JST in fog reaching into the airfield between
07-11Z Thursday. While model guidance does outline lower chances
for IPT/MDT/LNS clearing out, increased low- level moisture
coupled with easterly flow will retain some threat for fog/low
stratus potential; however, low confidence in this occurring.
Coastal low continues drifting east of the area with widespread
clearing expected after 12Z Thursday. Any fog/low stratus
development could linger through until ~14Z Thursday with
widespread VFR conditions progged by all model guidance after
14Z/15Z through the end of the TAF period.
Outlook...
Fri-Sun...VFR with AM valley fog.
Mon...Slight chance SHRA/PM TSRA possible across NW PA.
&&
.CLIMATE...
Astronomical fall officially begins with the autumnal equinox
on Monday, September 22, 2025 @ 2:19 p.m. EDT. The Autumn 2025
season will last 89 days, 20 hours, and 43 minutes. Daylight
saving time will end just after Halloween with clocks falling
back at 2 a.m. Sunday, November 2, 2025.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Lambert/Banghoff
NEAR TERM...Lambert
SHORT TERM...Lambert/Banghoff
LONG TERM...Lambert/Banghoff
AVIATION...NPB/Tyburski
CLIMATE...Steinbugl

NWS CTP Office Area Forecast Discussion