240
FXUS61 KCTP 191633
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1133 AM EST Sun Jan 19 2025

.SYNOPSIS...
*Quick-hitting, plowable/locally heavy snowfall expected today
*Arctic blast delivers bitter to extreme cold tonight-Wednesday
*Deep freeze ends late week with temperatures moderating closer
 to the historical average for late January by next weekend

&&

.NEAR TERM /THROUGH TONIGHT/...
945AM/1445UTC: Coordinated with PBZ on upgrade to winter storm
warning for Somerset County (adjacent to Fayette & Westmoreland
Ridges). A quicker onset of banded snowfall in conjunction with
recent HRRR runs and snow obs supports higher amounts
countywide to 5-8 inches. We already had a stripe of 6+ along
the Laurel Ridge so not a big stretch to tip scale to warning
criteria. Otherwise, fcst remains on track with snow now
covering all of south central PA.

Previous Discussion Issued: 807 AM EST Sun Jan 19 2025

"Finger" of snow extending northeastward from WV is quickly
expanding and blossoming over south central PA early this
morning per latest MRMS radar trends. Light snow has started in
State College is filling in over the southern half of central
PA. We adjusted POPs higher in the very near term to match a
more rapid onset of snow and adjusted hourly temps and maxT for
today as readings did not get as cold overnight to the south and
east of the Allegheny Plateau.

Previous Discussion Issued: 551 AM EST Sun Jan 19 2025

Arctic air is spilling into the northern tier of CPA early this
morning while much of south central and southeastern PA is still
hovering AOA the freezing mark at 10Z. Very shallow moisture
profiles combined with NNW upslope flow has sustained fzdz/fzfg
in the Laurel Highlands so watch out for slick spots heading
over the southwest mtns early this morning.

Radar trends are starting to show snow breaking out from
eastern KY into WV along max upper level divergence zone/left
exit jet region associated with shortwave trough expected to
pivot northeastward through the TN valley into the Mid Atlantic
by this evening.

Hires model guidance continues trend toward a better overall
consensus the heaviest swath of snowfall setting up early today
across south central PA then quickly moving to the northeast
through the mid/lower Susquehanna Valley into the Lehigh Valley
later this afternoon and evening. A slightly colder solution was
preferred this cycle with SLRs increased a bit in the southeast.
However, updated storm total snowfall amounts remained very
close to the previous forecast with max totals still in the 3-6"
range over the southern half of the forecast area. The only
change to the winter headlines was to add a few zones to square
off the northern edge of the advisory and trend more in line
with snow accumulation in the 2-3" range.

The period of heaviest snow is projected to be in the 12-6pm
timeframe maximized across portions of the lower Susquehanna
Valley where rates could exceed 1"/hr in the 2-5pm window based
on the 00Z HREF. A more prolonged period of the heavier rates
within a banding FGEN snow feature could deliver a boom
scenario of up to 7-8" locally.

Snow is projected to taper off and end btwn 00-03Z as dry arctic
air is directed into the area. Some lake enhanced/upslope snow
showers should linger over the NW Alleghenies and Laurel
Highlands with little additional accumulation through 12Z Mon.
Min temps dip into the +single digits to mid teens with min wind
chills ranging from -10F in the Laurels to +single digits int
the lower Susquehanna Valley.

&&

.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
Bitter cold and frigid MLK Day with highs 15 to 30 degrees below
the historical average. Snow showers and flurries are expected
to continue across the Allegheny Plateau with very light accum.

Based on minimum wind chills and collaboration with neighboring
offices, we transitioned to a longer duration cold wx advisory
Monday night for most of the area with high enough confidence
for an extreme cold warning for the Laurel Highlands for WCs as
low as 20 below zero. Later shifts could consider expanding the
cold wx advisory to include the remainder of the CWA with the
coldest period of WCs now looking like Tuesday night-Wed.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Cold weather products continue. Products updated to adjust
timing and area of concern.

As was the case yesterday, I did Tuesday onward, so not a lot
of change.

The main story continues to be the long duration cold through
the middle of the week. A northwest to southwest flow of cold
air will contiue, as high pressure builds to the south and west
of central PA, before ridging northwrad by Thursday.

For Central PA, high temperatures Tue-Wed will run 20-30 degrees
below average. Considering that late January is climatologically
the coldest time of the year, this will be a significant arctic
outbreak.

A wave of low pressure passing well to our south could brush
southeastern PA with some light snow for a very brief time
later on Tuesday. This system will coat the Gulf Coast states
with snow and ice before it lifts toward us. No warm place to
go for a winter break for a bit. 12Z EC hinted yesterday that
the primary jet stream might lift more to the north and become
more zonal by the end of the month, but not really a clear cut
signal in the guidance for this.

Thus after several very cold days, we will have to take what
mother natures provides, a brief moderating trend for late
week. Not seeing much in the way of weather after today and
Monday.

&&

.AVIATION /16Z SUNDAY THROUGH THURSDAY/...
MVFR conditions are occurring across much of central
Pennsylvania as of 11Z, though JST continues to report LIFR
ceilings and MDT remains VFR. Most guidance suggests that this
will largely continue for the next few hours.

A developing coastal low will bring a round of snow to the area
today. The snow will overspread the area from south to north
through the morning and early afternoon hours. Once the snow
begins, visibilities should quickly drop to IFR. All guidance
continues to show a period of heavy snow occurring at MDT and
LNS in the 18Z-00Z timeframe. This will likely lead to
visibilities falling to as low as 1/4SM at those sites.

The steady snow will pull east of the region Sunday evening
into Sunday night, although lingering upslope snow remains
possible across the western highlands Sunday night. As the snow
exits the region, ceilings will gradually rise to VFR east of
UNV and AOO, while MVFR ceilings are expected to persist to the
west. While winds will generally be light most of the day, model
soundings suggest that a few gusts to 20-25 knots will be
possible this evening.

Outlook...

Mon...MVFR to IFR conds in snow showers across mainly
northwestern PA; colder areawide with gusty west winds.

Tue...No sig wx expected; very cold.

Tues night-Wed...Scattered snow showers possible, bringing
localized restrictions; very cold.

Thu...No sig wx expected; continued cold.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Cold Weather Advisory from 4 AM Monday to noon EST Wednesday
for PAZ004>006-010>012-017-018-037-041-042.
Winter Weather Advisory until 8 PM EST this evening for PAZ012-
017-018-041.
Winter Weather Advisory until 10 PM EST this evening for
PAZ019-024>028-034-035-042-045-046-049>052.
Cold Weather Advisory from 7 PM Monday to noon EST Wednesday
for PAZ019-025>028-034-035-045-046-049>053.
Cold Weather Advisory from 4 AM Monday to 1 AM EST Tuesday for
PAZ024-033.
Extreme Cold Warning from 1 AM Tuesday to noon EST Wednesday
for PAZ024-033.
Winter Storm Warning until 8 PM EST this evening for PAZ033.
Winter Storm Warning until 10 PM EST this evening for PAZ036-
053-056>059-063>066.

&&

$$

SYNOPSIS...Steinbugl
NEAR TERM...Steinbugl
SHORT TERM...Steinbugl
LONG TERM...Martin
AVIATION...Evanego/Bauco