Latest Area Forecast Discussion for Central PA

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.

436
FXUS61 KCTP 230420
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1120 PM EST Thu Jan 22 2026

.WHAT HAS CHANGED...
* Increasing chances for heavy snow this weekend. More details
provided in discussion section.

&&

.KEY MESSAGES...
1) Frigid temperatures and dangerous wind chills expand from
northwest to southeast Friday afternoon into Saturday morning

2) Increasing odds for double digit heavy snow accumulation and
widespread moderate to major winter storm impacts Saturday
night through Monday morning, heaviest on Sunday.

3) Arctic blast persists with frigid temperatures and subzero wind
chills expected next Monday all the way through next weekend.

&&

.DISCUSSION...
KEY MESSAGE 1: Frigid temperatures and dangerous wind chills
expand from northwest to southeast Friday afternoon into
Saturday morning.

Arctic air is poised to return to the forecast area - filtering
in from northwest to southeast through Friday night. High
confidence in -10 to -20F wind chills across all of central PA
Friday afternoon into early Saturday morning approaching extreme
cold criteria in the Laurel Highlands. Frigid Arctic air will
remain in place prior to the onset of the significant winter
storm this weekend.

KEY MESSAGE 2: Increasing odds for double digit heavy snow
accumulation and widespread moderate to major winter storm
impacts Saturday night through Monday morning, heaviest on
Sunday.

Snow accumulations will likely begin with a vengeance from south
to north in the predawn hours Sunday. Periods with snowfall
rates greater than 1 inch per hour are becoming increasingly
likely in the isentropic ascent early Sunday and as low and
midlevel frontogenesis becomes stronger later in the day and
evening. Given the dry, fluffy snow and wind gusts of 15-30 mph,
there will likely be some blowing and drifting. There could be
a period of sleet especially across the southern tier Sunday
evening cutting into snow totals just a bit, but not before
double digit accumulations are expected to fall.

While warm advective, front-end snow is becoming increasingly
likely, there is considerable model uncertainty with the
placement of a comma head area of snowfall as a secondary low
pressure system develops offshore (in a Miller B type
evolution). If the comma head sits over central PA Sunday night,
several additional inches of accumulation are possible. However,
if it misses us to the north and we see more of a dry slot, that
would result in snow ending sooner Sunday evening with less
accumulation overnight.

All in all, the probability of snowfall amounts exceeding 12
inches has increased to 60-80 percent across much of central
PA. The probability of more than 18 inches ranges from 15 to 40
percent. Amounts near 24 inches can`t be ruled out (10 percent
chance) especially if the comma head sits over central PA Sunday
night. Always prepare for the worst case scenario and continue
to check the forecast as it evolves. Now is the time to prepare.
Think snow blowers, re-arranging travel plans to avoid travel
during the storm, what to do in case of a power outage, etc.
Remember it will be very cold before, during and after the
storm. Never run a generator indoors due to carbon monoxide.

Now if you really enjoy meteorology and want to know *why* we
are predicting the most significant accumulations in the past
5+ years, feel free to read on through the remainder of this KEY
MESSAGE 2 discussion. We`ve had our fair share of cold snaps
this winter season, and tomorrow (Friday) will be no exception
after the next Arctic front pushes through. A large factor
driving all this cold weather has been the Polar Vortex
displaced from the North Pole, with a tendency for the vortex to
find itself over Hudson Bay and northern Quebec. With
displacement that far south, we`ve gotten plenty of cold air,
but it`s also nudged the storm track south of our area for many
of the recent events. If you`ve ever heard people say "it`s too
cold to snow", it`s not that it`s physically too cold to snow,
it usually just means that the storm track has shifted far
enough to the south that we end up under dry high pressure while
our temps are cold.

One key difference this time is the influence of a Pacific
storm, located off the coast of southern California this
evening, and a strengthening subtropical jet to its south. Over
the next 24 hours these features will cross the Baja Peninsula
of Mexico and then into Texas. Southwesterly flow out ahead of
this southern stream feature will pump warmer air into the Gulf
Coast and Southeastern US Saturday night into Sunday. At the
same time, a northern stream shortwave trough coming down from
western Canada into the Great Plains will bring a reinforcing
shot of cold air to the back side of the northern longwave
trough. The increasing temperature gradients will result in an
overall increase in wind speed aloft at jet stream altitude, and
an amplification of the northern stream trough and ridge. By
Sunday, the right entrance region of the northern jet and the
left exit region of the southern jet will align to produce
enhanced upward motion through the troposphere. Remaining
uncertainty in the forecast largely depends on the degree of
phasing of these two jets, the angle at which they align, and
how much amplification there is of the ridge out ahead of the
deepening trough.

The very cold air in place ahead of this system also plays other
crucial roles to increase impacts. At 00Z Sunday, model
consensus depicts a 1040+ mb high over New York State, which
only slowly moves northeastward across New England over the next
24 hours. The deep, cold blocking high to the northeast of a
winter storm is a textbook feature that supplies a stream of
cold air down the Alleghenies and provides a cold dome for
warmer, less dense air parcels streaming in from the southwest
to ascend over. That upward motion is key to production of
hydrometeors - in this case snow. And then there is the key role
that cold temperatures have on ice crystal habits. The so
called "dendritic growth zone" exists where temperatures are
between roughly 0F and 10F. Given low temperatures Saturday
night in the single digits, some spots might start off with a
DGZ that extends from the ground up 10,000 to 15,000 feet which
is pretty remarkable for a large synoptic storm in this region.
As long as the column saturates quickly enough, any snow that
falls late Saturday night and into early Sunday morning could be
very high ratio, fluffy, rapidly accumulating snow that
consists of many pristine dendrites (SLRs 15-20:1, could be
even higher if the column saturates faster but there is dry air
at low levels to overcome at onset). So after a few hours of
virga, accumulations have the potential to begin with a
vengeance in the predawn hours Sunday, especially from I-80
south.

KEY MESSAGE 3: Arctic blast persists with frigid temperatures
and subzero wind chills expected next Monday all the way through
next weekend.

A prolonged stretch of frigid temperatures continues next week
through the end of January (next weekend). After the cold snap
Fri night - Sat, the next round of cold wx headlines (-10 to -20F
wind chills) is likely Monday night through Tuesday morning.
Given the prolonged nature of the bitter cold, we may begin to
see more infrastructure impacts (frozen pipes) by next week.

Occasional lake effect/upslope snow showers are likely next week
under a very cold cyclonic flow aloft.

&&

.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
Mostly clear skies are expected across the forecast area
overnight outside of BFD/JST and MDT/LNS which will likely
experience cloud cover overnight based on most recent HREF model
guidance. Across southwestern Pennsylvania (JST), highest
probabilities for cloud cover come between 23/00Z-04Z with more
dry air in place further east, which will limit cloud cover at
AOO with high (~70-80%) confidence. Cloud cover currently across
western New York will continue to gradually shift southward and
get into BFD after 23/01Z and is likely to continue through the
rest of the 00Z TAF package, with MVFR conditions becoming more
likely after 23/09Z. Recent model guidance does indicate some
scattering out of the low-level (below 3000ft AGL) cloud deck at
BFD with a period of VFR conditions in the 23/10Z-13Z
timeframe; however, low (~20%) confidence in this solution at
this juncture. Cloud cover is also progged by the bulk of model
guidance to begin filtering into southeastern Pennsylvania after
23/09Z, thus have included mentions in VFR ceilings at MDT/LNS
with moderate-to-high (~60-80%) confidence.

Gusty to breezy winds are expected to continue overnight with
some periods of relatively lighter winds progged by recent
GLAMP/HREF model guidance. The 00Z TAF package has increased
winds and gusts slightly higher than previous forecasts based on
current observations with winds expected to stay stead and/or
increase overnight across the area ahead of a moisture-starved
Arctic Front passage across central Pennsylvania expected early
Friday morning. Gusty winds are expected with high (~80-90%)
confidence after the passage of this Arctic Front with gusts
between 20 and 30 knots expected area wide.

Outlook...

Sat...Dry most of the day, then SN begins to enter south-to-
north late spreading across region and intensifying overnight.
Widespread IFR likely Sat night.

Sun...Impactful snow storm continues with widespread IFR
restrictions, LIFR possible.

Mon...Storm lifts to the NE and cold northwest flow takes over,
bringing snow showers and continued restrictions to the NW, and
improving conditions to the SE.

Tue...Lake effect snow across NW PA with restrictions possible;
otherwise, dry and breezy.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Cold Weather Advisory from 1 PM Friday to 10 AM EST Saturday
for PAZ004>006-010>012-017-018-037-041-042.
Winter Storm Watch from Saturday evening through Monday
afternoon for PAZ004>006-010>012-017>019-024>028-033>037-041-
042-045-046-049>053-056>059-063>066.
Cold Weather Advisory from 6 PM Friday to 10 AM EST Saturday
for PAZ019-025>028-034-035-045-046-049>053.
Extreme Cold Watch from Friday evening through Saturday
morning for PAZ024-033.
Cold Weather Advisory from 10 PM Friday to 10 AM EST Saturday
for PAZ036-056>059-063>066.

&&

$$

WHAT HAS CHANGED...Steinbugl/Colbert
KEY MESSAGES...Steinbugl/Colbert
DISCUSSION...Steinbugl/Colbert
AVIATION...NPB

Forecaster's
Discussion: