Harrisburg, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

311
FXUS61 KCTP 222350
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
650 PM EST Mon Dec 22 2025

.SYNOPSIS...
* A quick-hitting system will bring up to a several hour period
  of snow with a coating to 2 inches across central and
  northern PA tonight with some light mixed precipitation early
  Tuesday morning; travel impacts possible
* Breezy conditions Tuesday night precede a sunny and seasonable
  Christmas Eve (day)
* Light rain possible (mainly SW) later Christmas Eve and
  Christmas morning; light mix possible in central mountains
* Turning milder with several chances for rain Christmas Day
  into the weekend

&&

.NEAR TERM /THROUGH TUESDAY/...
Abundant sunshine and a developing light swrly sfc breeze has
erased the earlier, strong sfc based inversion and caused about
a 12-14F jump in temps over the past 3 hours - into the mid and
upper 20s across the Northern Mtns and low to mid 30s
respectively in the Central and Southern Valleys.

Thickening high/mid clouds will overspread the area from west to
east this afternoon. Removed low pop mention of light SN from
Central and Northern PA later this afternoon as the airmass is
very dry in the low levels. A few flakes of snow could reach the
sfc around or shortly after dusk across the Northern and Western
Mtns, but the main, 3-5 hour period of light snow will likely
hold off until after midnight in most places. Afterward, the
nose of a 45-50 kt, WSW 850 mp jet moves into the CWA and
enhances WAA/UVVEL over the dome of llvl cold air across the
CWA as quickly blossoms/expands the snow through the late
night/predawn hours of Tuesday.

The precip type across the north and east will remain snow for
much of the night and early morning. So, accumulations are
likely - mainly N of a MDT to AOO line. The QPF is unimpressive
with at most 0.20" of frozen in the NE where SLRs will be 10:1
at first, but slide lower thru the night, eventually finishing
around 5:1 around noon Tues. Thus, max snow/sleet amounts will
likely be ~2" from Potter to Sullivan counties. Up to an inch is
possible down to I-80, tapering off to nothing by the MD
border. Whatever does fall as frozen or freezing precip should
melt away.

Afternoon high temps today will be around 30F on the ridge tops
and in the lower 40s along and south of the PA Turnpike.

&&

.SHORT TERM /TUESDAY NIGHT/...
Slightly above freezing wet bulb temps in about a 2-3 kft thick
layer will advect east into Central PA after the main forcing
with the LLJ and sfc-850 mb warm frontal boundary lifts to the
east. This will create a brief period of very minor, light
mix of precipitation for the early to mid morning hours
Tuesday that will likely end as rain/drizzle as temps warm into
the low to mid 30s.

High temps Tues will vary from near 50F in the S and upper 30s
in the far NE.

The questions...Just how much ZR falls (it will certainly be
<0.10" everywhere it may fall), and - Will it even cause
problems for the places where it snows/sleets first? With only
medium certainty on the answers to those questions, we may go
the eventual SPS route (per collaboration with CLE PBZ and BUF)
and hold off on issuing any advisories at this point. We
shouldn`t need any advisories for snow.

The wind gets gusty (10-12,G20-25KT) Tuesday night, but won`t
last long.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
The main weather features for this period are #1 - the minor
shortwave/warm-cold front tandem that brings very minimal light
mixed precip Christmas morning and #2 a stronger upper shortwave
and surface low with even a several hour period of llvl easterly
flow ahead of a warm front leading to a several hour period of
snow just ahead of a warm front.

Concerning #1 - The majority of models keep the measurable
precip late Christmas Eve and Christmas morning to the SW of FIG
and AOO. It would also be just warm enough to be mainly -RA.

Any light precip will quickly turn to plain rain before ending
later Christmas morning. Temps soar on Christmas Day with upper
30s NE and mid 50s SW.

WNW wind gusts will increase Tuesday evening to the teens and
20s (with some gusts into the 30s possible early Wed) as
building high pressure creates a tightening pressure gradient
with a retreating wave of low pressure. Winds shouldn`t be much
of a factor by late Wednesday morning as high pressure moves in
and the pressure gradient weakens.

Wednesday holds some potential for temps to get warmer than
expected, but will be a milder day as 8H temps rise to the mid-
single digits (C). But, the subsidence inversion will be
holding the top of the mixed layer down around 2kft. Therefore,
we`ll hang close to the NBM guidance for the time being. Highs
range from the mid 30s north to upper 50s south. The fast flow
will keep pushing high clouds in from the NW. Forcing comes
over the top of a ridge over TX and the Deep South after coming
ashore in SoCal.

Clouds will thicken up Wed night (Christmas Eve) and eventually
could bear some precip - mainly for the SW half of the CWA. The
timing is still moderately uncertain, but the trend on the GFS
is centering on any precip starting after 06Z. The ECMWF is much
drier and would delay precip until Thurs. Temps Wed night will
probably be very much like Monday night, but the precip lighter.
So, there is a chc for --ZR over the NErn half of the CWA early
Christmas morning. However, the moisture feed and precip
amounts are still suspect.

Christmas day will hold a good warm up, turning any potentially
frozen or freezing precip to plain rain. Maxes certainly not
Christmas-like for PA with the Laurels 15-20F above normal (esp
if the clouds can break a little), with the eastern zones
about 5F warmer than normal.

Beyond Thursday, the GFS and ECMWF diverge with the former
making a cold front push thru Fri and the latter surging warm
air into the Great Lakes and PA. That would delay the arrival of
a colder airmass until later in the weekend. Therefore, the
forecast for the weekend is highly uncertain. NBM seems to be
weighted heavily toward having the cold air arrive earlier
rather than later. Without any confidence then, we`ll just defer
to the NBM output for that period.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
Cloud cover will continue to increase through the evening ahead
of an approaching disturbance, though conditions likely remain
VFR through at least 06Z. An initial area of light snow will
move through this evening, but dry air in the low levels should
limit just how heavy the snow gets. Because of this, confidence
is too low to include any restrictions with the 00Z TAF package.

Restrictions will quickly develop as mixed precipitation enters
from the west after 08Z, though there is still quite a bit of
uncertainty regarding precip type at most TAF sites. After an
initial mix of rain, snow, and freezing rain at BFD, UNV, and
AOO, expect light freezing rain or freezing drizzle to become
the predominant ptype after sunrise. Model soundings show warmer
air reaching JST quicker, likely resulting in a quick
transition to plain rain. IPT has the best chance of seeing
steady snow with this system as they should stay coldest the
longest. MDT and LNS will likely see a few hours of rain or
snow, but it will be fairly light. Confidence in this forecast
is low and adjustments to precip type and visibility will likely
be needed.

Precipitation decreases in intensity after 18Z though drizzle,
low clouds, and reduced visibility will linger through the rest
of the day. A 45 knot low-level jet will move into southwest PA
during the afternoon resulting in a period of LLWS for JST, AOO,
and UNV.

Outlook...
Wed...Lingering restrictions in the west, otherwise VFR with
plenty of sunshine. Increasing clouds late.

Thu...Scattered rain showers, some FZRA possible.

Fri-Sat...Widespread -SN developing (with restrictions),
possibly changing to sleet or a brief period of -ZR Friday
night.


&&

.CLIMATE...
Astronomical winter (solstice) began at 10:03 a.m. on December
21st. Daylight lasted 9 hours and 15 minutes. We can look
forward to the following milestones:

10 hours of daylight: January 29th
11 hours of daylight: February 22nd
12 hours of daylight: March 17th
13 hours of daylight: April 9th
14 hours of daylight: May 2nd
15 hours of daylight: June 6th

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 1 AM to noon EST Tuesday for
PAZ005-006-010>012-017>019-045.
Winter Weather Advisory from 1 AM to 9 AM EST Tuesday for
PAZ025>027.

&&

$$

SYNOPSIS...Lambert/Dangelo
NEAR TERM...Lambert/Dangelo
SHORT TERM...Lambert/Dangelo
LONG TERM...Dangelo/Banghoff
AVIATION...Lambert/Bauco
CLIMATE...Banghoff