Welsh Run, Pennsylvania Weather Forecast Discussion

601
FXUS61 KCTP 051125
AFDCTP
Area Forecast Discussion
National Weather Service State College PA
725 AM EDT Sun Oct 5 2025
.SYNOPSIS...
* Dry conditions with above-average temperatures continue
  through Monday under the influence of high pressure stationed
  south of the region.
* Increased rain chances Tuesday through Wednesday morning with
  an approaching cold front.
* Dry conditions return for the second half of next week with
  overnight low temperatures pushing closer to the freezing
  mark.
&&
.NEAR TERM /THROUGH TONIGHT/...
Current (as of 0730Z/3:30 AM EDT) ECONUS Nighttime Microphysics
outlines valley fog formation across the deepest valleys of
Pennsylvania, which is expected to continue slowly expanding
through sunrise. Current observational systems outline no
restrictions below 4SM and anticipate any visibilities below
1/4SM to be limited to the typical valley locations through
12Z/8 AM EDT, thus no DFA/SPS consideration this morning across
central Pennsylvania.
Fog is expected to quickly dissipate with another sunny-to-
mostly sunny day across the forecast area as high pressure
continues to build to the south. Biggest forecast challenge
today will remain dew points with extremely dry air (~10-15% RH
at 700mb) aloft above a weak inversion. This will allow for dry
air to mix down to the surface and almost certainly requires
undercutting on NBM dew points. MinRH readings this afternoon in
the 25-35% range seem the more probable solution; however, spot
RHs pushing closer to the ~20% mark could be in the cards
across south-central Pennsylvania in the 2-7 PM timeframe.
Despite low RH values and recent dry conditions, high pressure
influence keeps winds fairly low with sustained winds generally
below 10 mph across the forecast area, which will keep any RFW
considerations out of the picture this afternoon.
&&
.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
All model guidance points to continued dry conditions on Monday
as high pressure stationed south of the region begins to push
eastward into the northern Atlantic. Overall, a similar
environmental set-up will be in place across central
Pennsylvania with morning valley fog potential across mainly the
northern half of the Commonwealth. The main difference
pertaining to surface dew points, where dry air stationed aloft
will be notably less dry on Monday as moisture returns
increase, especially by the afternoon hours. Cloud cover will
begin to increase late Monday evening and continue into the
overnight hours as a surface low pressure begins to track
northeastward into Ontario, which is expected to limit fog
potential Monday evening into Tuesday morning.
&&
.LONG TERM /TUESDAY THROUGH SATURDAY/...
The aforementioned (short-term) surface low pressure system
continues to shift northeastward into northern Ontario/Quebec in
the beginning stages of the long-term forecast period. This
track allows for a cold frontal passage to occur across central
Pennsylvania Tuesday into Wednesday morning. Rain chances start
to increase Tuesday late morning/early afternoon generally in a
northwest-to-southeast across the forecast area with the bulk of
precipitation expected to occur through Wednesday afternoon
based on recent GEFS plumes. There remains some model disparity
in timing; however, with the best chances of precipitation
across the northwestern half of the CWA mainly in the Tuesday
afternoon/evening timeframe. QPF returns continue to look
overall unimpressive in terms of a "drought-busting" with
current QPF form this system generally under one inch across the
entire forecast area, in fair agreement with recent
deterministic model guidance, outside of the ECMWF that does
outlines spot amounts just above one inch. At this time, have
leant towards the GFS solution, as instability remains to appear
weak, thus general thought is that it will be harder to come by
those spot amounts reaching over one inch.
Dry conditions (once again) seem to be in play as the cold
front clears the region by Wednesday afternoon/evening as high
pressure builds into the region. Recent model guidance shows
fair agreement with regards to the aforementioned 1032mb high
pressure setting up directly over the region, allowing for clear
skies and ample radiational cooling across central Pennsylvania
Wednesday night and Thursday night. Freeze concerns are
becoming increasing likely across the northern tier of
Pennsylvania on Wednesday night, with recent NBM guidance
outlining near-to-sub 32 degree temperatures across portions of
McKean and Potter Counties for multiple cycles. Frost concerns
appear increasingly likely for the bulk of the area Wednesday
and Thursday nights outside of the south-central and Lower
Susquehanna Valley zones; however, less confidence on the
southeastward extent at this time.
Fair amount of uncertainty resolves towards the end of the
long-term forecast period with recent deterministic model
guidance outlining two separate solutions for the Friday and
Saturday forecast periods. Main source of uncertainty comes with
respect to the upper-level pattern. First solution outlines an
amplified trough at 500mb bringing some rain chances to central
Pennsylvania later on in the afternoon/evening Friday and into
Saturday morning. While the second solution outlines a slightly
less amplified upper-level trough potentially leading to less
rainfall chances. Given the spread in model guidance, have
decided to roll with NBM this cycle.
&&
.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
A very dry air mass continues overnight. Will maintain
generally VFR/unrestricted conditions and light winds through
the forecast period.
Went with persistence for the potential for patchy valley fog
toward the end of the forecast period as dry airmass will
saturate little over the next 24 hours.
Outlook...
Mon...AM Fog (Mainly N PA); otherwise VFR.
Mon night...Incr clds, SHRA poss W toward sunrise.
Tue...Sct SHRA. TSRA poss W & S late.
Tue PM...CFROPA. SHRA. TSRA poss. IFR fog poss mainly NW.
Wed...Sct AM SHRA SE. Otherwise becoming VFR.
Thu...AM fog then VFR.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...NPB
NEAR TERM...NPB
SHORT TERM...NPB
LONG TERM...NPB
AVIATION...Tyburski

NWS CTP Office Area Forecast Discussion