Back-to-Back Pacific Storms to Impact the West Coast; Heavy Snow in the Central Appalachians

Back-to-back powerful Pacific storm systems to impact the Pacific Northwest and northern California through the end of this week with heavy rain, flooding, strong winds, and higher elevation mountain snow. A strong, long-duration atmospheric river will accompany the Pacific storms, bringing excessive rainfall and flash flooding to southwest Oregon and northwest California through the week. Read More >

Here is the latest Area Forecast Discussion for Central PA

This text statement is the latest forecast reasoning from the NWS in State College, PA

See the links at the bottom of the page for previous issuances/versions of the statement as well as our other text statements.

495
FXUS61 KCTP 211052
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
552 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 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 /UNTIL 4 PM THIS AFTERNOON/...
A dry slot has moved into Central PA early this morning in the
wake of an occluded front passage last evening. However, falling
heights and upper level diffluence ahead of an upper low over
Lower Michigan will spread snow/rain showers into the western
half of the forecast area later this morning. 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.

&&

.SHORT TERM /4 PM THIS AFTERNOON THROUGH FRIDAY NIGHT/...
Overall confidence is continuing to increase for the first
impactful winter weather storm of the season tonight into
Friday, 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.

Model thermal profiles are cold enough to support primarily snow
over the forecast area tonight into Friday, with some rain
possible tonight over the Lower Susq Valley. However, 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.

The highest confidence of heavy snow is focused over
high-elevation Sullivan County, as well as the Laurel Highlands,
where the 00Z HREF supports a likely period of 1-inch/hr rates
between 10-16Z Friday. The greatest impact to travel should be
late tonight through Friday morning. Most likely snow totals by
late Friday should range from up to a foot over the highest
elevations of Somerset and Sullivan counties, to an inch or so
from Altoona/State College into the Susq Valley.

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 /10Z THURSDAY THROUGH MONDAY/...
06z update... A frontal band of rain showers is progressing
quickly across the Commonwealth and it should be through
central PA by 08-09z. MVFR restrictions are the most likely
scenario during this timeframe, mainly for KIPT.

A dry slot behind the front should result primarily in
unrestricted conditions through early to mid-afternoon (17-20z).
Confidence in this scenario is fairly high (70-80%) for most
central PA terminal sites. The exception to this is along the
Allegheny front at KJST, where we expect lower clouds to
redevelop by 11-14z. We have 50-60% confidence in this.

Later this afternoon and evening, conditions should deteriorate
at KIPT (light rain and snow), as well as KBFD and KJST (light
snow). KJST will likely see IFR reductions (70-80% confidence),
with KBFD also probably sinking into IFR conditions by later
this evening. If KIPT keeps a rain/snow mix, MVFR is foreseen,
but prevailing snow would mean lower visibilities and IFR.

KAOO, KUNV, KMDT, and KLNS are expected to stay unrestricted
(60-80% confident) through this evening.

Gusty W-NW surface winds will diminish for a time later this
morning, before picking up again later this afternoon and
tonight (gusts of 20-25 kt common).

Outlook...

Fri-Sat...Restrictions likely with 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. Windy.

Sun-Mon...Lingering showers near KBFD and KJST.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 1 PM this afternoon to 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 from 1 PM this afternoon to 7 AM EST
Saturday for PAZ024-033.
Winter Storm Warning from 4 PM this afternoon to 4 PM EST
Friday for PAZ042.

&&

$$

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

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