Shellsville, Pennsylvania Weather Forecast Discussion

355
FXUS61 KCTP 040821
AFDCTP
Area Forecast Discussion
National Weather Service State College PA
421 AM EDT Sat Oct 4 2025
.SYNOPSIS...
* Dry, pleasant early Autumn weather over this weekend and into
  early next week with well-above normal temperatures.
* A cold front will push east across Pennsylvania late Tuesday
  into Wednesday morning bringing a few periods of showers.
* Dry and cooler conditions return for the second half of next
  week with overnight low temperatures approaching the freezing
  mark in the northern tier and colder valleys of central PA.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Meso ob data showing most sites are at a 0 or 1 deg F T/Td
spread at 0730Z and GOES-19 night fog channel was showing plenty
of valley fog forming throughout the Allegheny and Susq West
branch tributaries in Northern PA. Fog coverage will expand
significantly in the Central and southern valleys over the next
few hours and will be keeping a watchful eye on the possibility
of issuing a Dense Fog Advisory for at least portions of
Central and Northern PA.
The perennial cold spots will dip to around 40F at sunrise, but
most locations will settle into the 45-50F range.
After the valley fog dissipates between 9 and 10 AM, expect a
spectacular late morning and afternoon today with abundant
sunshine, light wind, low humidity and afternoon max temps
in the upper 70s to low 80s equating to temp departures of
12-17 deg F above normal on average, which are similar to
normal temps in late June or Early August. Still, record high
temps for the date are 5+F greater than the forecast highs.
A weak subsidence inversion is favorable for mixing of much
drier air from aloft and cutting sfc dewpoint values below most
guidance and strongly blending in lower, NBM 25th percentile
values.
Per previous discussion - Don`t want to go too wild with a
departure from guidance. But, did nudge mid-day/aftn dewpoints
down a few degs from NBM, esp in the mtns and Lower Susq.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
Mainly clear skies tonight with just some patchy thin cirrus
drifting SE across the region. Min temps will average 2-3 deg F
higher tonight and valley fog wont be quite as extensive. min
temps will range from the mid 40s (NW) to the low 50s in the
Lower Susq Valley.
Sunday will be a near carbon copy of today (Saturday), with
respect to sky cover, high temps, wind, and RH.
&&
.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
The dry and warm pattern Sunday night through Monday night will
give way to the next opportunity for rain by Tue-Wed as surface
low pressure from the central US tracks northeastward into
Ontario. The low will drag a cold front through the area,
bringing some rainfall to central Pennsylvania.
While there should be decent moisture return ahead of the front,
with PWAT values rising to the 1.25-1.4 inch range (~90th
percentile for this time of year), there is still some
uncertainty as to just how much rain will fall. Ensemble mean
QPF is generally around 0.50 inch in northwest PA, with lesser
amounts as you move south and east, but some of the
deterministic guidance, namely the 12Z GFS, continues to show
the potential for over an inch of rain over parts of central PA.
This does not appear to be the most likely solution at this
point, however, as most guidance shows the best synoptic scale
forcing passing well to our north and more detached from the
tropical moisture stream. Additionally, weak instability should
help to limit rainfall rates.
All guidance shows high pressure building into the region at the
surface and aloft in the wake of the cold front. This setup
would allow for another spell of dry weather into the latter
half of the week. With a 1030 mb surface high expected to be
centered over the region Wednesday and Thursday nights, ideal
radiational cooling conditions are anticipated with mainly
clear skies and light winds. Temperatures will fall into the 30s
and 40s both nights and frost formation is likely over the
north and west. There is also some potential for temperatures to
drop below freezing Wednesday night across the northern tier and
colder valleys of central PA.
&&
.AVIATION /07Z SATURDAY THROUGH WEDNESDAY/...
Clear skies are currently being observed across central
Pennsylvania with some valley fog beginning to form across the
northern tier. High clouds are expected to stream in over the
next couple of hours across western Pennsylvania which could
limit some fog potential into BFD/JST/AOO overnight. Do expect
to see a short timeframe of IFR at BFD in the 06-07Z timeframe;
however, the confidence on this continuing throughout the entire
hour is low at this time. Higher confidence in clear skies
prevailing overnight across the Susquehanna Valley, with highest
probabilities of fog formation at IPT. Non- zero chances of fog
formation remain at all airfields, but confidence remains too
low for mentions in the TAFs outside of some visibility
restrictions between 09-11Z Sat at AOO/UNV.
After 11-12Z Sat, VFR conditions are virtually certain through
06Z Sunday under the influence of high pressure. High clouds
will continue streaming across central Pennsylvania with
relatively dry air filling in and allowing for skies to trend
clear by the afternoon/evening hours.
Outlook...
Sun-Mon...AM Fog (Mainly N PA); otherwise VFR.
Tue...Sct SHRA.
Tue PM...CFROPA. SHRA. TSRA poss. IFR fog poss mainly NW.
Wed...Sct AM SHRA SE. Otherwise becoming VFR.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Lambert
NEAR TERM...Lambert/Colbert
SHORT TERM...Lambert
LONG TERM...Colbert/Bauco/NPB
AVIATION...NPB

NWS CTP Office Area Forecast Discussion