FXUS61 KCTP 131410
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1010 AM EDT Sun Oct 13 2024

.SYNOPSIS...
A warm front extending east from low pressure near Toledo
this morning will bring warmer air back to the Keystone state
today, along with periods of light to moderate rain showers
across the Northern Mountains and just a chance of mainly
afternoon showers today or perhaps even a thunderstorm.

A cold front will push through tonight, bringing much colder
air to the region from Monday into Thursday, before temperatures
moderate later in the week. The cold air will result in a daily
chance of showers and even the first snowflake of the season
across the Northern and Western Mountains. Temperatures will
average well below normal.

&&

.NEAR TERM /THROUGH TONIGHT/...
10 am update... An area of showers, with some embedded, elevated
thunder, continues to track across northeast OH, western and
northern PA, and much of NY State late this morning. As the
previous discussion mentioned, this region of precipitation is
in the area of strongest warm air advection forcing on the nose
of an 850 mb jet (about 5000 feet AGL). Near-term, high
resolution model guidance generally indicates a gradual
northward retreat of this shower activity into NY State through
the afternoon, as the core of the aforementioned low-level jet
ultimately pulls east and north of central PA.

The approach of a surface low pressure wave from the OH Valley
and its trailing cold front later this afternoon into the early
evening should lead to a broken band of showers and
thunderstorms tracking across the Commonwealth. The latest
consensus is that this band of showers and storms moves through
northwestern and central PA from roughly 5 to 10 pm. Given the
expectation of a fair amount of sunshine through early to mid-
afternoon over much of south-central PA within the warm sector
of the above mentioned approaching cyclone, we'll have to watch
for how much destabilization can occur, as the environment today
does exhibit deep vertical shear. At the current time, though,
our expectation is that the majority of the buoyancy (anything
more than 200-400 j/kg of MLCAPE) will stay west of the
Alleghenies and also south of the Mason-Dixon line.

Highs this afternoon should range from the upper 50s over the
northern tier (cloudy and rainy) to the upper 70s (more
sunshine) for many areas near and south of US-22/I-78.

Previous discussion... The nose of a 35 to 45 kt west-southwest
925-850 mb jet was helping to fuel moderately strong theta-E
advection in that same layer with several large areas of light
to moderate rain showers racing east across the northern third
of the state.

Much of the CWA to the south of Interstate 80 will see partly
sunny skies and very little rain today, prior to one or two bkn
lines of showers and maybe even a rumble of thunder occurring
along and just ahead of a potent cold front draped south from
the aforementioned low as it moves east, along or just to the
north of I-80.

Latest NAM and HREF are the most bullish on a narrow NE/SW wedge
of enhanced CAPE around 1000 J/KG forming over the South-Central
Mtns/Laurel Highlands during the mid afternoon and sliding east
to near the I-81 corridor by dusk. SPC trimmed its previous MRGL
risk area to the south of our CWA today

Decent vertical mixing of the WSW LLJ will lead to wind gusts of
30 to 35 mph late this morning through the mid afternoon across
the Laurel Highlands and possibly east to the I-99 corridor in
Scent PA.

Model 850mb temps near 14C could support highs in the low 80s
across the low elevations south of the PA Turnpike while
afternoon maxes near the I-80 corridor will be in the low to mid
70s and only in the upper 50s to Low 60s across the Northern
Tier counties.

Likely 18-24 hour rainfall totals by this Sunday evening (based
on ensemble plumes ranges from around 1 inch over the N Mtns,
to around 0.10 inches along the Mason Dixon Line).

The cold front should exit the eastern part of the forecast
area by around 06Z Monday. Focus then shifts to a potent
shortwave and associated reinforcing cold front, which is
progged to sweep across the area Monday morning. This feature is
likely to be accompanied by another round of showers in many
locations and followed by gusty northwest winds.

&&

.SHORT TERM /MONDAY/...
Dry air and low inversion heights behind an exiting shortwave
should limit lake effect rain shower activity over most of the
Alleghenies Monday. However, models indicate moisture
pooling/low level convergence along an inverted surface trough
will result in the best chance of lingering rain showers into
Monday afternoon over Southern Somerset County.

Ensemble mean 850mb temps Monday of 0 to -2C support max temps
from just 45-50F over the Allegheny Plateau, to near 60F in the
Lower Susq Valley. Latest EPS plumes and Bufkit soundings
support wgusts of 30kts+ Monday with mixing up to 750mb.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Model consensus indicates the coldest air of the season at 850
mb will overspread central PA by Monday night and Tuesday. 850
mb temps drop below -6C in some spots within this air mass
Monday night and Tuesday, which could even support wet snow over
the northern tier counties into Tuesday morning as sfc low
tracks across my northern zones. Elsewhere, a tight pressure
gradient sets up in the wake of the cold front, and the brisk
northwest flow traversing anomalously warm Lake Erie waters will
keep cloud cover in the forecast for much of the northwest
mountains and Laurels through the week ahead. Cloudiness will be
accompanied by occasional lake effect showers as a few lobes of
the upper low support increased instability. Lake effect
showers will likely persist through Tuesday and possibly
Wednesday, with wet snowflakes still a possibility given -2 to
-4C airmass persisting at 850 mb into Wednesday.

The chilly air mass will be the main story next week as Monday
to Wednesday temperatures are likely to be 5 to 15 degrees below
normal seasonal normals. Highs in the 40s and 50s along with a
brisk northwest wind will feel raw. Overnight lows will likely
drop near or below freezing in the northwest mountains and
Laurels each morning (most likely Tuesday morning), with mid to
upper 30s elsewhere. With winds expected to stay up each night
through early Wednesday, frost should not be much of a concern.

By Wednesday, high pressure will approach Pennsylvania and shut
off the lake effect clouds/rain in northwest PA, potentially
setting up a chilly enough night to bring the growing season
across much of Central PA to an end.

For late next week through next weekend (10/19-10/20) a large
sfc ridge and highly amplified and slowly progressive upper
level ridge will move from the midwest to the east Coast by
Sunday 10/20. There is good model agreement in this, so we'll
paint a dry and quite mild weekend for peak fall foliage
viewing with overnight lows in the mid 30s to low 40s and
daytime highs well above normal - in the upper 50s (Northern
Mtns) to mid 60s Southern Valleys.

&&

.AVIATION /14Z SUNDAY THROUGH THURSDAY/...
Rain will continue along and north of I-80 ahead of an
approaching low pressure system into the morning. A few
lightning strikes have been occurring over western PA, but
confidence is too low in any thunderstorms reaching BFD to
include it in the TAF. Ceilings are VFR at almost all TAF sites,
with BFD being the exception where ceilings are IFR. Model
soundings show IFR ceilings remaining at BFD for the rest of the
morning before becoming MVFR for the afternoon. IFR ceilings
will return though during the evening and will persist through
the night.

LLWS will be possible for a few more hours at JST, AOO, and UNV
before wind gusts begin to increase. Model soundings suggest
that gusts of 15 to 20 knots will be likely across much of the
area, with gusts as high as 30 knots possible for JST and AOO.

As the low pressure system moves closer during the evening, a
cold front will track through the area and will bring more
showers and a few thunderstorms with it. Have introduced PROB30
groups at all airfields except BFD, MDT, and LNS for
thunderstorms, but the timing may have to be adjusted.

Outlook...

Mon-Wed...A chance of showers, mainly across the north and
west. Gusty winds.

Thu...Dry weather with VFR conditions.

&&

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

&&

$$

SYNOPSIS...Lambert/Martin
NEAR TERM...Jurewicz/Lambert/Tyburski
SHORT TERM...Lambert/Tyburski
LONG TERM...Lambert/RXR
AVIATION...Bauco