Lancaster, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

717
FXUS61 KCTP 211558
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1058 AM EST Thu Nov 21 2024

.SYNOPSIS...
 * An upper level low over the Lower Great Lakes will track
   southeast across Pennsylvania tonight into Friday.
 * The first impactful winter storm of the season will arrive
   with this low, bringing widespread snow across central
   Pennsylvania.
 * The upper low will lift out of the region this weekend, then
   a a cold front will likely push southeast across the state
   Monday night into early Tuesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
A strong surface low moving across western Michigan combined
with strong upper level diffluence and positive vorticity
advection will spread light rain/snow showers over the area
ahead of the main system. Model sounding are cold enough for
snow showers across the Alleghenies, but amounts should be light
and progged surface/road temps should be just above freezing,
so don`t expect many travel issues through mid afternoon. See no
reason to deviate from NBM temps, which peak this afternoon in
the low to mid 30s across the Laurel Highlands and the mid 40s
in the Susq Valley.

Overall confidence is continuing to increase for the first
impactful winter weather storm of the season to begin tonight,
as the closed 500mb low tracks across Southern PA, causing the
associated surface low south of New England to retrograde
westward through upstate NY. A deep, moist westerly flow on the
northern and western periphery of the upper low should result in
persistent orographically-enhanced precipitation over Central
PA tonight into Friday. Snow will be the primary form of
precipitation during the overnight hours with a mix of rain
possible in the Lower Susquehanna Valley. Marginal boundary
layer temps will result in highly elevation- dependent
accumulations across the Alleghenies and downsloping flow should
yield lower precip rates east of the Alleghenies.

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
Friday morning will see the heaviest snow fall across our CWA.
The highest confidence of heavy snow is focused over high-
elevation Sullivan County, as well as the Laurel Highlands,
where the 12Z HREF supports a likely period of 1-inch/hr rates
between 10-16Z Friday. The greatest impact to travel should be
very early Friday through late Friday morning, but caution
should be exercised when traveling throughout the day Friday as
snow showers will continue into the early afternoon. Most
likely snow totals by late Friday should range from up to a foot
over the highest elevations of Somerset and Sullivan counties.
The 12Z HREF has trended snowfall amounts slightly higher from
previous runs with the mean snowfall for Altoona and
Statecollege now between 2-3 inches. Areas across the Lower
Susquehanna will likely have 1-2 inches of snow given the more
marginal temperature profiles.

Diminishing precipitation is expected in general late Friday
into Friday night, as the upper low lifts out. However,
lingering lake effect will affect the W Mtns. Forecast thermal
profiles moderate with the departure of the upper low to the
point that lake effect snow showers may mix with rain over the
Alleghenies Friday night.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Lingering lake effect/orographic rain showers over the Northern
and Western Mountains Saturday, as one or more fast-moving and
weak shortwave moves SE from the Glakes Region. This light
precip will dwindle by late Sunday afternoon, as subsidence
inversion heights fall and high pressure approaches from the
Tennessee Valley. Milder conditions look likely next Monday
ahead of an approaching, rather potent cold front, which could
produce late afternoon/early nighttime rain showers with the
core of energy aloft progged to move across the Upper Great
Lakes region.

Brisk west winds and colder air pushing into the region for
Tuesday with scattered rain showers in the valleys and mixed
rain/snow showers over the higher terrain of the Laurels and NW
Mtns.

&&

.AVIATION /16Z THURSDAY THROUGH MONDAY/...
12z update... Areas of fog have formed just prior to daybreak
near KIPT, so we did include brief IFR restrictions only til
around 13z.

Otherwise, lower clouds and some flurries will have the upper
hand today at KBFD and KJST, with mostly MVFR restrictions (high
confidence in this scenario - 80 to 90%). Unrestricted/VFR
should prevail during the daylight hours at KUNV, KAOO, KIPT,
KMDT, and KLNS.

Tonight, conditions should deteriorate from south to north with
time, as steadier snow wraps down and around an incoming storm
system. KIPT, KBFD, KUNV, and KJST should all see IFR reductions
in snow prior to daybreak (60-70% confidence). Restrictions at
KAOO, KMDT, and KLNS should occur after 12z.

Surface winds 10 kt or less for much of today, should increase
and become gusty late tonight and Friday (gusts of 20-25 kt
common, locally up to 30 kt).

Outlook...

Fri...Restrictions in snow at KBFD and KJST, with a period of
snow likely elsewhere (mostly before 18-19z). Windy.

Sat...Periodic restrictions in rain and snow showers, mainly
across the mountains (KBFD and KJST). MVFR much of the time for
KUNV/KIPT/KAOO. Mainly VFR at KLNS and KMDT. Continued breezy.

Sun-Mon...Lingering restrictions possible at KBFD and KJST,
otherwise mainly VFR.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 7 AM EST Saturday for PAZ004-005-
010>012-017-018.
Winter Storm Watch from 4 PM EST this afternoon through Friday
afternoon for PAZ006-037-041-058.
Winter Storm Warning until 7 AM EST Saturday for PAZ024-033.
Winter Storm Warning from 4 PM this afternoon to 4 PM EST
Friday for PAZ042.

&&

$$

SYNOPSIS...Fitzgerald/Bowen
NEAR TERM...Fitzgerald/Bowen
SHORT TERM...Fitzgerald/Bowen
LONG TERM...Lambert
AVIATION...Jurewicz