829
FXUS61 KCTP 260317
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1117 PM EDT Wed Sep 25 2024

.SYNOPSIS...
Damp and unsettled weather will persist into Thursday, with
perhaps a brief dry break Thursday night into early Friday. A
stationary front draped across the Mason-Dixon Line will bring
an increasing chance of showers for late Friday and into the
weekend. A steadier period of rain is possible over parts of
Central Pennsylvania Saturday night or Sunday as the weakened
moisture remnants of Helene very slowly pull away from the
region.

&&

.NEAR TERM /THROUGH THURSDAY/...
Persistence rules as easterly ageostrophic flow and western
Atlantic component being overrun by moisture WSW flow at 850mb
and above, yielding dense low clouds cover and widespread
drizzle and patchy light rain this evening. Current conditions
will persist for most of tonight and Thursday, as central PA
remains sandwiched between an upper- level trough crossing New
England and upper low centered over the Lower Ohio Valley.

Blanket of clouds will keep overnight temperatures mild, with
lows in the upper 50s to mid 60s running about 15 degrees above
normal for late September. Thursday should be a bit milder
than the past few days, with highs expected to reach the 70s
areawide.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
Little in the way of changes for Days 2 through 4 as the upper-
level trough over New England moves off the the Atlantic Coast
Thurs night into Friday, while the moisture remnants of Helene
become wrapped up in the upper low over the Lower Ohio Valley.

At the sfc, a stationary front will become draped across
southern Pennsylvania. We will have to see how the remnant
moisture from Helene interacts with the stationary front. The
trend is for rainfall farther north and sooner on Friday, but
the location of the aforementioned front will determine how far
north showers travel, and how long they remain in the forecast
into this weekend, esp across southern PA.

Temperature-wise, the days will see temperatures fairly close
to average, while clouds will keep nighttime temperatures well
above average for early fall.

There is still some uncertainty in regards to how Helene will
impact central Pennsylvania, mainly dependent on interactions
with an upper-level low stationed across the eastern Tennessee
Valley. Deterministic model guidance has outlined that the bulk
of rainfall will stay west of the area while a rather narrow,
negatively tilted upper-level ridge holds strong from the Great
Lakes through the Upper Ohio River Valley. Given the uncertainty
with regards to upper-low interactions, did not deviate much
from continuity and NBM guidance this cycle.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
11 PM Update is mainly to nudge some PoPs upward. Big upper low
creeps in from the OH Valley and still has some moisture in it
despite entraining lots of continental air during the short term
period. Slight ridging aloft could provide enough of a break to
actually give us a entire dry day by the end of the long range.

Prev...
An upper-level low over the Ohio Valley will likely drift east
across the Commonwealth into the beginning of next week, keeping
rain chances around through at least Tuesday. Uncertainty begins
to increase towards the middle of the week as a northern stream
shortwave tracks near the region, bringing a cold front along
with it. The timing of this feature is a little unclear with
some ensemble members showing the front tracking through early
Wednesday morning while others show a later frontal passage.
Moisture appears to be limited ahead of the front and the best
forcing looks to remain to our north, so widespread rainfall
does not appear likely at this point.

Most guidance shows high pressure building in behind the front
which will bring drier weather and cooler temperatures. By
Wednesday, expect high temperatures in the upper 50s and 60s and
lows mainly in the 40s.

&&

.AVIATION /03Z THURSDAY THROUGH MONDAY/...
03Z update holds no changes. While IPT is still MVFR, expect
them to drop to IFR shortly. UNV sky/cig sensor appears to be
down. So, for safety, we`ll keep the forecast there in IFR all
night with LIFR past 07Z and improvement to MVFR gradually from
sunrise to noon local.

Prev...
While there has been a slight uptick in cigs here and there
over the last hour or so, most terminals are still IFR. IPT had
it`s cig improve as a larger patch of rain came through. This
may have been because the rain precipitated out the finer
droplets of clouds/DZ. Still, IFR ceilings are expected to
persist into Thursday mid-day along with patchy rain and fog
that will be worst on the windward (SE, in this case) side of
the ridges.

Model soundings and MOS guidance support widespread ceilings
below 500 feet overnight at all airfields, and the HREF suggests
a 30 to 40% chance of LIFR fog developing across the northern
half of Central PA.

Ceilings may slowly rise Thursday afternoon with most guidance
showing MVFR ceilings in the northwest after 15Z and after
18-19Z elsewhere. Patchy RA/sct SHRA will continue into the
early afternoon.

Outlook...

Fri...Patchy AM valley fog possible N Mtns. Chance of
showers/low cigs across the south.

Sat-Mon...Chance of low cigs/showers, mainly across the south.

&&

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

&&

$$

SYNOPSIS...DeVoir/Evanego
NEAR TERM...DeVoir/Evanego
SHORT TERM...DeVoir/Evanego
LONG TERM...Dangelo/Bauco/NPB
AVIATION...Dangelo/Bauco