Halls, Pennsylvania Weather Forecast Discussion

848
FXUS61 KCTP 171010
AFDCTP
Area Forecast Discussion
National Weather Service State College PA
610 AM EDT Wed Sep 17 2025
.SYNOPSIS...
* Several bands of light to moderate rain/showers pushing west
  across the Susquehanna Valley and South-Central Mountains of
  PA today and tonight, with the coolest high temperatures of
  the week occurring today.
* Rainfall amounts generally between one tenth and one quarter
  of an inch. Locally over one half of an inch across portions
  of the Lower Susquehanna Valley.
* Dry conditions return areawide on Thursday and will persist
  through the weekend with temperatures rebounding to well-above
  normal.
&&
.NEAR TERM /THROUGH TONIGHT/...
Slowly weakening and northward moving low pressure (1012 MB) was
located over the southern tip of Delaware at 07Z. A persistent
and slightly increasing, deep easterly flow will combine with
several spokes of diff PVA and increasing mid level FGEN
forcing/diffluence aloft to push several bands of light to
briefly mdt/hvy showers westward over the SE 1/3 of of CWA today
into early tonight.
Near, and just to the SE of the I-99/RT 220, a few lighter rain
showers will likely occur, but won`t amounts to more than a
few/svrl hundredths of an inch in most places.
This same easterly flow, downsloping west of the Alleghenies,
will bring dry conditions and significant breaks in the cloud
cover, along with temps as much as 10-12F above normal near and
to the west of RT 219 in the NW Mtns.
The generally thick cloud cover across the SE two thirds of the
CWA, persistent easterly flow will keep temperatures
significantly cooler than recent days.
Look for high temps in the upper 60s to near 70s along and to
the south/east of I-99/I-80, while locations farther west soar
into the 80s.
SFC dewpoints will rise another several deg F acrs the Susq
Valley and crest the 60F mark for the first time in quite awhile
as tropical moisture swirls into the region accompanied by
PWATs over 1.5". Along with this, a layer of elevated
instability will be advecting westward across the Lower Susq
Valley and Southern Poconos late this morning through this
afternoon. 925-850 mb Lifted Indices via the 06Z NAM will dip
to -2 to -4 at 18z, near and to the SE of Interstate 81. This
will support the slight chc/chc for some TSRA with brief
downpours in that part of the CWA.
The radar at times today may show returns extending into
northern PA (north of I-80). However, a deeper layer of dry air
at low levels should prevent most of the rain from reaching the
surface there, though. Rainfall totals by this evening will
range from locally up to 0.5" across the Lower Susq Valley to
little or nothing over the NCent and NW Mtns.
For tonight, the aforementioned coastal low will move off the NJ
coast and the single, closed-contour upper level low will
transition to a positive-tilt. open wave causing the low to mid
level flow to back through the NE then North by morning. This
will lead to a significant decrease in POPS and areal coverage
for showers by or shortly after midnight tonight.
&&
.SHORT TERM /THURSDAY THROUGH FRIDAY/...
Satellite imagery over Central PA at daybreak may be quite
striking as numerous valleys in northern PA become blanketing by
fog for 2-3 hours around/shortly afternoon daybreak.
Thursday and Friday will be a continuation of what we`ve seen
for a majority of the past couple weeks with plenty of sunshine,
seasonably mild temperatures, and light winds. It will take a
little while for the moisture in southeast PA to be replaced by
a drier airmass, so expect the air to feel a bit humid still on
Thursday. Highs will generally be in the 80s with lows in the
upper 40s (NW) to lower 60s (SE). A backdoor, moisture-deprived
cold front will sag south into northern Pennsylvania Friday
afternoon, with an increase in cloud cover north of US-6 being
the only noteworthy aspect of its arrival. Drier air awaits in
its wake...
&&
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Friday night - the aforementioned backdoor cold front will
slide through Pennsylvania with a strong 1028mb high surging in
behind it. Dewpoints will plummet by Saturday morning,
supporting a return to below-normal overnight temperatures with
clear skies and calm winds. Surface high pressure will set up
off the New England Coast for the weekend, ensuring moist
southeast flow and tranquil weather. Highs will tick down a few
degrees for the weekend, with highs in the 70s and lows in the
50s most likely at this time.
Heading into next week, high pressure will begin to lose its
grip on the region as an upper trough tries to disrupt the
persistent ridge of high pressure aloft. Still plenty of
uncertainty on how much, if any, precipitation will get into
Pennsylvania but southerly flow ahead of the approaching system
will support continued warmer than average temperatures for the
start of Astronomical fall.
&&
.AVIATION /10Z WEDNESDAY THROUGH SUNDAY/...
Showers will continue to rotate into southeastern PA on the
northwestern side of a low pressure system currently located
east of Maryland and will continue to impact MDT and LNS for
much of the day. Ceilings will gradually lower at these two
sites as well, though most guidance continues to back off on
just how low clouds get. The GLAMP continues to suggest that a
prolonged period of IFR ceilings will be possible, particularly
at LNS, but most model RH profiles show a shorter window between
15Z and 21Z where cloud bases are more likely to drop below
1000 feet AGL. That being said, there is a small chance (20%)
that ceilings remain MVFR through the TAF period at those sites.
Showers gradually expand northward through the day and may
reach as far north and west as UNV and IPT. Those sites, along
with AOO, may see a period of MVFR ceilings as showers approach,
but confidence is not high on that occurring. While there has
been a few lightning strikes observed this morning around MDT
and LNS, weak instability should limit the lightning threat
today. Winds will generally be out of the northeast at 5 to 10
knots with a few gusts to 15 knots possible in southeast PA.
Showers gradually shift eastward as the low moves away from the
area, and will come to an end by 00Z.
Widespread fog formation appears likely across much of the area,
with IFR cigs/vsby possible at all TAF sites after 06Z. The
timing of these restrictions will need to be refined with later
forecasts.
Outlook...
Thu...Generally VFR.
Fri-Sun...VFR with AM valley fog.
&&
.CLIMATE...
Astronomical fall officially begins with the autumnal equinox
on Monday, September 22, 2025 @ 2:19 p.m. EDT. The Autumn 2025
season will last 89 days, 20 hours, and 43 minutes. Daylight
saving time will end just after Halloween with clocks falling
back at 2 a.m. Sunday, November 2, 2025.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Lambert/Banghoff
NEAR TERM...Lambert/Banghoff
SHORT TERM...Lambert/Banghoff
LONG TERM...Lambert/Banghoff
AVIATION...Bauco
CLIMATE...Steinbugl

NWS CTP Office Area Forecast Discussion