927
FXUS61 KCTP 040754
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
354 AM EDT Fri Oct 4 2024

.SYNOPSIS...
* Valley fog redevelops overnight; clouds and a stray shower
  possible over east-central PA later Friday and Friday night
* A great start to the first weekend of October; rain showers
  return from NW->SE later Sunday through Sunday night
* Drying out and cooling down next week with frost risk

&&

.NEAR TERM /UNTIL 8 AM THIS MORNING/...
Fog has begun to fill in the West Branch and tribs N of UNV.
The valley fog should continue to expand. Thus far, not bad or
widespread enough for a fog advy. Lower clouds moving up from
the S are not solid as of yet. 00Z NAM continues to be the most
aggressive model at cloud coverage/spread northward. Thus far,
it`s too aggressive. We`ll keep with the going fcst of overcast
not quite getting up to I-80 by sunrise.

SEG the cold spot at 51F at 02Z. Low temps will range from
mid/upper 40s in the northern tier to mid 50s along the MD
border (+5-10F above the historical average for early October).
When clouds arrive/develop in the S, they might help temps go up
a couple degs, and almost certainly level them off.

&&

.SHORT TERM /8 AM THIS MORNING THROUGH SUNDAY/...
Valley fog and low clouds to start the day on Friday. Model
guidance indicates a shortwave trough rotating through the lower
Great Lakes tomorrow afternoon/evening coinciding with a surge
of low level moisture in advance of a weak sfc cold front. These
features will combine to drive low POPs over the northern and
eastern portions of the CWA through Friday night.

Warm advection preceding the cold front should push temps into
the low to mid 70s Friday afternoon with the largest anomalies
over the Allegheny Plateau, where the most sunshine is expected.

High pressure and an associated low-pwat airmass is progged to
build southeast into PA Saturday, providing the region with
mostly sunny skies. Ensemble mean 850mb temps in the 7-9C range
support highs ranging from the mid 60s over the N Mtns, to the
mid 70s in the Lower Susq Valley. Have undercut NBM dewpoints
Sat afternoon based on model soundings, which show very dry air
above a weak inversion.

Fair and seasonable weather appears likely into the second half
of this weekend, as surface high pressure builds across the
state. We`ll continue to slightly undercut NBM min temps
Saturday night, when conditions favor efficient radiational
cooling directly under the surface high. This will also be
favorable for morning fog across typical fog prone areas across
the Commonwealth through the weekend.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Increasing clouds ahead of the next chance of showers are
expected Sunday night as a cold front approaches central
Pennsylvania. This forecast continues to outline the best
chances for rainfall in the overnight period into Monday morning
across the northern tier and the Laurel Highlands. Rainfall is
expected to continue with a east/northeasterly progression
throughout the Monday morning hours. Instability continues to
look fairly limited to the earliest hours Sunday night across
the western highlands along with the Lower Susquehanna Valley,
so have retained SChc of thunderstorms in this period. Storm
chances decrease closer to daybreak on Monday, so have limited
precipitation mentions to just showers this forecast cycle.

Enhanced westerly flow in the wake of the cold front will allow
for lingering showers across mainly NW PA throughout the day on
Monday. Guidance does outline high pressure beginning to build
into the area late Monday and into the mid-week allowing for
drier conditions to prevail for the bulk of central PA although
have retained low-end SChc PoPs across NW PA on Wednesday with
enhanced westerly flow continuing throughout the period.

High pressure influencing the area will allow for clear/mostly
clear skies which does promote undercutting NBM MinTs Tuesday
and Wednesday nights. The combination of clear skies, light
winds,and cooler temperatures start to bring the first concerns
of frost into the forecast across N PA. Have introduced frost
mentions on Tuesday night given a slightly more favorable set-
up for frost formation while limiting mentions on Wednesday
night due to more uncertainty, but given similar environmental
set-up, subsequent forecast packages may need to introduce
frost mentions for this period.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
Fog concerns begin entering the forecast area again, with the
highest probabilities in HREF guidance lighting up at AOO
(09-13Z Friday) and UNV (10-13Z Friday) with lower- level cloud
decks being the main concern. There is some spread in model
guidance with GLAMP being less keen on any restrictions
throughout the period; however, given a combination of previous
GLAMP model cycles, RAP model soundings, and HREF probs, have
outlined a period of MVFR/IFR conditions throughout this
timeframe. There is moderate (40-50%) confidence in restrictions
at AOO/UNV with lower confidence on low-level moisture
manifesting further east at IPT/MDT/LNS overnight.

Any valley fog that does form begins to mix out ~14Z Friday
with VFR conditions expected outside of the Lower Susquehanna
Valley through 18Z Friday with moderate (~60%) confidence.
Guidance does suggest a lower-level (~2-4kft) cloud deck making
way into LNS/MDT for a period of MVFR ceilings early in the day
before scattering back towards VFR in the 18-20Z Friday
timeframe.

Outlook...

Sat-Sun PM...Patchy AM Valley Fog; otherwise, VFR prevails.

Sun PM-Mon...SHRA moves in west-to-east, some TSRA possible.

Tue-Wed...VFR, no sig wx.

&&

.CLIMATE...
Total precipitation for the month of September was 1.11 inches
at Williamsport (-3.65" below average) which ranks as the 11th
driest on record.

The average temperature for the month of September was 63.1
degrees at Bradford (+4.2F above average) which ranks as the
warmest September on record.

Harrisburg (MDT) consecutive days streak of measurable rain
ends at 9 with only a trace recorded yesterday 10/2. This ties
the record for longest such stretch set from April 7-15, 1893
and matched May 15-23, 1893 and July 28-August 5, 1971.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SYNOPSIS...Steinbugl
NEAR TERM...Dangelo/Steinbugl
SHORT TERM...Fitzgerald/Steinbugl
LONG TERM...NPB/Bowen
AVIATION...Gartner/Bowen
CLIMATE...Steinbugl/Banghoff