611
FXUS61 KCTP 150544
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
144 AM EDT Mon Sep 15 2025

.SYNOPSIS...
* Clearing skies tonight with river valley fog probable for the
  morning commute across northern Pennsylvania.
* High confidence in dry weather continuing through Tuesday.
* Light rain possible mid-to-late week, especially across
  southeast Pennsylvania.

&&

.NEAR TERM /THROUGH TODAY/...
Recent satellite loop shows fair weather cumulus falling apart
at sunset with high clouds streaming into southeast PA from the
DelMarVA. Valley fog potential looks more favorable tonight
compared to this morning given the overall lack of mid- to-high
level clouds. Recent HREF probabilities are pushing closer to
40-50% for valley fog formation across the northern valleys of
Pennsylvania, with a secondary area of fog formation possible
across Lancaster, Lebanon, and favored areas in Schuylkill
County. At this time, the northern tier looks like the better
bet, thus have highlighted this potential slightly heavier in
this forecast package. Low temperatures overnight based on MAV
guidance under radiational cooling outlines MinTs in the upper
40s across NW PA to the upper 50s across the southern tier.

Rinse and repeat for Monday (with more emphasis on the repeat
than rinse). High pressure keeps abundant sunshine and dry
conditions across the region. We`ll see a bit more high cloud
cover than previous days being on the north side of an upper low
centered over the southeast. Easterly flow and some fair weather
cumulus will be accompanied by afternoon temperatures quite
similar to today (Sunday) ranging from the mid 70s to low 80s.

&&

.SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/...
All model guidance points to fair weather under high pressure
stationed over Ontario/Quebec and into the northeast CONUS,
allowing for continued dry conditions through Tuesday with high
confidence. Increasing cloud cover with easterly flow will
allow for a slight decrease in temperatures on Tuesday, pushing
closer to seasonal averages with portions of the southeastern
Pennsylvania tipping just below average for mid-September. Dew
points will be the trickiest part of the forecast on Tuesday.
Some signals for relatively dry air aloft mixing down are
present with the MinRH "floor" reaching down towards the 20-25%
range across portions of west-central Pennsylvania to 30-35%
across the northern tier.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
A closed low stationed across the southern Mid- Atlantic will
bring increased chances for precipitation chances on Wednesday
and into the second half of the week. Recent deterministic model
guidance has began to converge towards the low pressure system
setting up along the VA-NC border on Wednesday which will bring
about some chances of precipitation across southern and eastern
Pennsylvania; however, model guidance still shows a fair amount
of spread with respect to track of the low, thus there remains
uncertainty later in the week. The current forecast outlines
the best chances for showers and (afternoon/evening)
thunderstorms across southern and eastern Pennsylvania on
Wednesday. Would expect the gradient of QPF on the north side of
the system to tighten as lead time decreases, and would not be
surprised if rainfall totals remain less than 0.10" for anywhere
in our CWA given antecedent dry conditions.

A brief spell of dry conditions is once again expected in the
wake of the coastal low, with moderate-to-high confidence in dry
conditions on Friday. Recent model guidance has slightly slowed
down with respect to the low pressure system in the Midwest
with a fair amount of uncertainty between deterministic model
guidance. Given these changes, have decided to roll with NBM
through Sunday, with the best chances of precipitation coming
after sunrise on Sunday.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
Valley fog can be seen forming on satellite as of 06Z and will
continue to expand across north-central PA, and potentially
southeast PA, into the early morning. We have kept all TAFs VFR
with the 06Z package as confidence on impacts remains low. Model
soundings suggest that the best potential for any reduced
visibility would be at BFD, IPT, and LNS. Fog will dissipate by
14Z, giving way to VFR conditions.

Varying amounts of high clouds will be in place during the day
on Tuesday as a coastal low well to our southeast moves slowly
northwestward. The greatest amount of cloud cover will be over
the southeast, while areas north of I-80 may see mainly clear
skies for much of the day. The clouds will decrease in coverage
after 06Z, allowing for valley fog formation.

Outlook...

Tue...VFR with AM valley fog. Isolated SHRA possible late for
SE PA.

Wed-Thu...Generally VFR, some SHRA possible (20-40%) SE PA.

Fri...VFR with AM valley fog.

&&

.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...NPB
NEAR TERM...NPB
SHORT TERM...NPB
LONG TERM...NPB
AVIATION...Bauco
CLIMATE...Steinbugl