York, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

594
FXUS61 KCTP 241125
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
625 AM EST Sat Jan 24 2026

.WHAT HAS CHANGED...
* Winter Storm Warning in effect for Central Pennsylvania with
  widespread double-digit snow accumulation still expected
  Saturday night through Monday morning

&&

.KEY MESSAGES...
1) Frigid temperatures and dangerous wind chills ongoing into
Saturday morning

2) Widespread double digit heavy snow accumulation will result
in moderate to major winter storm impacts Saturday night
through Monday morning

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
ongoing into Saturday morning.

Bitter cold arctic air has arrived in full force with
temperatures plummeting early this Saturday morning. 4AM
temperatures at KBFD is -13F with much of northern and central
mountains and Laurel Highlands below zero. Even a light wind
producing a high confidence in -10 to -25F wind chills across
all of central PA through mid morning. Extreme Cold Warning for
Cambria and Somerset Counties and cold wx advisory elsewhere
remains in effect. The frigid Arctic air will remain in place
prior to the onset of the major winter storm this weekend.

KEY MESSAGE 2: Widespread double digit heavy snow accumulation
and moderate to major winter storm impacts Saturday night
through Monday morning

Forecast remains largely on track with only minor changes
compared to the previous cycle. What could go wrong? Typical
uncertainty surrounding the depth and northward push of the mid
level warm nose. This shows up the most along and south of the
PA Turnpike where sleet/freezing rain could cut down on snow
totals.

Previous Discussion with minimal edits:

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 50-80 percent across much of central
PA. The probability of more than 18 inches ranges from 15 to 25
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 /12Z SATURDAY THROUGH WEDNESDAY/...
VFR conditions will continue through the daylight hours today
as a powerful winter storm moves toward central Pennsylvania. A
high overcast will gradually lower through the day as winds
slowly shift to an easterly direction.

Snow will overspread the area from west to east toward midnight,
quickly dropping conditions to MVFR and IFR over the higher
elevation airfields. Conditions will deteriorate rapidly after
midnight through the mid-early morning and continue through the
remainder of the forecast period.

Outlook...

Sun...Highly impactful snow storm continues all day with
widespread LIFR in heavy snow with LLWS areawide.

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 until 10 AM EST this morning for
PAZ004>006-010>012-017>019-025>028-034>037-041-042-045-046-
049>053-056>059-063>066.
Winter Storm Warning from 10 PM this evening to 1 PM EST
Monday for PAZ004>006-010>012-017>019-024>028-033>037-041-042-
045-046-049>053-056>059-063>066.
Extreme Cold Warning until 10 AM EST this morning for PAZ024-
033.

&&

$$

WHAT HAS CHANGED...Steinbugl/RXR
KEY MESSAGES...Steinbugl/Colbert/RXR
DISCUSSION...Steinbugl/Colbert/Bauco/RXR
AVIATION...Tyburski