730
FXUS61 KCTP 260553
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
153 AM EDT Thu Sep 26 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 TODAY/...
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 /TONIGHT 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 /06Z THURSDAY THROUGH MONDAY/...
06z update... IFR conditions (low ceilings and light rain) are
probable (70-80% confidence) at the central PA terminal sites
through early afternoon (17-19z).

There is medium confidence (50-60%) that ceiling bases will
elevate a bit this afternoon, allowing nominal category
improvements into the fuel alternate-MVFR ranges.

By this evening (00-03z), the expectation is that ceiling bases
will lower again to categorical IFR reductions (70-80%
confidence).

Surface winds of 5-8 kt from the E-SE can be anticipated this
afternoon, with otherwise light and variable winds less than 5
kt.

Outlook...

Fri...Areas of morning fog and low ceilings possible area-wide,
then the best chance of showers/low ceilings across southern PA.

Sat-Mon...The highest probabilities for low ceilings and
showers should again be across southern PA.

&&

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

&&

$$

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