Altoona, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

810
FXUS61 KCTP 211853
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
153 PM 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 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 THURSDAY/...
One last channel of vorticity stretched out to the west of the
center of the upper low will enhance lift on Sat along the
western mtns. That will help precip (mainly rain) linger over
the western hills. It`s a high-PoP but low QPF event. This
light precip will dwindle Sunday AM, as subsidence inversion
height fall and high pressure approaches from the Tennessee
Valley. Milder conditions (+3 to 6F vs Sun) look likely for
Monday. A fast-moving but compact system will develop very
quickly as it near from the OH valley, and pass across the
state Monday-Monday night. Temps should remain mild enough to
be almost all rain except on the very highest (>2000ft)
elevations. No accums are expected at this point, but a slight
timing change (time of day/night) may allow a slushy coating.
Tues looks mainly dry under high pressure. Perhaps a SHSN NW.

The next 2 days (peak travel Wed and Thanksgiving Day itself)
seem highly uncertain. A zonal flow across the ern 2/3rds of the
CONUS will likely lead to a fast, progressive flow. The front
that passed thru on Mon night will be laid out W_E to the south
of our latitude, and moisture should start to return and pool up
along it on return flow from the GOMEX. However, timing of
support/forcing from the west is highly uncertain. GFS Ensembles
have low spread in 5H and thickness plots, with a very, very
dip/trough developing to our west mid-week. 00Z ECMWF is much
(1 day) slower with generating a sfc low and making precip
arrive in PA (not until Turkey Day), vs the GFS which is faster.
Thermal profile for the start of any precip either Wed or into
Thurs would likely be cold enough over some (nrn) portion of
the CWA to make frozen or freezing precip. Following the NBM`s
very slow building/ramp up in PoPs without any notion of support
for deviation at this point. Just not enough strong points to
make any precip arrive slower or faster. Be prepared for
slippery/poor travel during this upcoming long holiday travel
time.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...

The winter season has begun. SN falling lightly in many
terminals at times. Temps are mild enough for RA lower elevs and
SN high. But, everyone cools down this evening just as the upper
low to our NW slides overhead and deepens. This will back the
precip over ern PA and NY into the CWA, dropping in into IPT and
BFD this evening, and UNV overnight. The cigs and vis will drop
to IFR at all those locations by sunrise. At the same time, the
NW flow at the sfc will bring in lake moisture and begin to
drop snow on the Laurel highlands. JST will have SCT SHSN thru
the night, but the upslope flow will solidify for all day Fri
and into Friday night. Expect more snow on the highest
elevations, but airport ops will be impacted/disrupted Fri AM.

The cold precip over the nrn half of the state will continue to
drop southward on Fri. Expect MDT and LNS to get precip (mostly
rain, but a few hours of snow is also likely) thru the bulk of
the day on Fri. Intensity will be light, but it will be around
for 12+ hrs. Expect icing to be widespread over the region.

The wind will pick up quickly tonight, and be gusting into the
20s areawide and perhaps above 30kts at JST and AOO on Fri.

Outlook...

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.

Tues...MVFR cigs/isold SHSN NW, VFR SE.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 7 AM EST Saturday for PAZ004-005-
010>012-017>019-025-034-045.
Winter Storm Warning from 4 PM this afternoon to 4 PM EST
Friday for PAZ006-037-041-042-053-058.
Winter Storm Warning until 7 AM EST Saturday for PAZ024-033.
Winter Weather Advisory from 4 PM this afternoon to 4 PM EST
Friday for PAZ046-049-051-052.

&&

$$

SYNOPSIS...Fitzgerald/Bowen
NEAR TERM...Fitzgerald/Bowen
SHORT TERM...Fitzgerald/Bowen
LONG TERM...Dangelo
AVIATION...Dangelo