Harrisburg, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

683
FXUS61 KCTP 040859
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
359 AM EST Wed Dec 4 2024

.SYNOPSIS...
* Cold and breezy conditions continue through the end of the
  week with temperatures below the historical average for early
  December
* Widespread snow showers, localized snow squalls, and strong
  winds 40-50 mph will likely result in hazardous travel
  impacts late Wednesday night into Thursday
* Lake effect and upslope snow continues into late week with
  significant storm total accumulations probable in the favored
  snowbelts and higher ridgetop elevations

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A few light snow showers remain possible through late this
evening in the vicinity of a stalled surface trough over North
Central PA, where there remains a narrow ribbon of instability
and low level convergence. Otherwise, boundary layer flow
backing to the southwest will push lake effect snow showers
north of the border tonight.

Low level moisture trapped beneath a subsidence inversion,
combined with an upsloping WSW flow, should yield persistent
stratus over the Allegheny Plateau tonight. Elsewhere, mostly
clear skies and a diminishing breeze should allow temps to fall
a bit below NBM guidance tonight. However, model soundings
indicate thickening mid and high level cloudiness will
overspread the entire region late tonight, putting the breaks on
radiational cooling.

WAA ramps up Wednesday ahead of a deepening upstream trough,
with thickening mid and high level clouds indicated by model RH
profiles. There could even be a bit of very light snow or
flurries, mainly over the N Mtns where a southerly flow is
forced to ascend the higher terrain north of I-80. See no reason
to deviate from NBM max temps, which range from around 30F over
the N Mtns, to around 40F across the Lower Susq Valley.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY/...
A deepening upper level trough tracking through the Great Lakes
will push an arctic cold front through the area Wednesday night
and early Thursday morning. Steep lower tropospheric lapse rates
and sufficient low level moisture support the possibility of an
intense burst of snow squalls accompanying the front, leading
to potentially hazardous travel conditions, particularly over
the Laurel Highlands and Allegheny Plateau with near-blizzard
conditions possible, as strong wind gusts arrive with the front.

Any snow associated with the front should be in the half inch
to 2 inch range. However, lake effect snow showers will then
develop behind the cold front Thursday into Thursday evening,
with a WNW boundary layer flow targeting the NW Mtns for
potentially heavy additional snow. A winter storm watch remains
up along the spine of the Alleghenies. However, highest
confidence in warning upgrades are across the lake effect
snowbelt regions of Warren/Mckean counties. Forecast time/height
progs support high snow/water ratios over the NW Mtns Thursday
PM with most lift occurring within the DGZ.

Forecast soundings and strong pressure rises/BL mixing behind
the sharp arctic cold front will support peak wind gusts 45-50
mph over the majority of the area Thursday. We issued a wind
advisory for the entire CWA from 1AM-7PM Thursday. However,
latest model guidance indicates the onset of the strongest winds
may be a bit later than 1AM.

Inversion heights fall a bit Thursday night into Friday, causing
lake effect snow showers to diminish somewhat. However, a cold
WNW flow should continue to produce persistent light lake effect
snow across primarily the NW Mtns.

Friday will be another cold day, as some of the greatest 850mb
temp anomalies pass over the state. Expect highs at or below
the freezing mark across most of central PA. Daytime max
temperature departures from the historical average will be 10 to
20 degrees! Wind chills Friday morning will be in the single
digits to mid teens. Lake effect snow should be in the late
innings heading into Friday night as mean trajectories start to
back to the west- southwest.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
A WNW flow in the cloud bearing layer will likely maintain
lingering lake effect snow over the Northwest Mtns into Sat AM.
However, inversion heights look relatively low, so any
additional accumulation should be light. Fair and chilly
conditions appear likely Sat PM, as surface ridging builds
across the state.

Upper level ridging and a surface high passing off of the East
Coast should translate to fair and significantly milder weather
Sunday, as the return southwest flow develops. GEFS 2m temp
anomalies suggest highs will be several degrees above average,
ranging from around 40F over the N Mtns, to near 50F in the
southern valleys.

The bulk of medium range guidance supports a period of rain
Monday associated with warm advection ahead of a weakening
shortwave lifting into the Eastern Grt Lks. Can`t completely
rule out an initial wintry mix over the higher terrain Monday
AM, but lack of a blocking high and current progged thermal
fields point toward rain. The low level jet and plume of
highest pwats should shift east of the region by Monday night,
causing rain to taper off. Ensemble plumes currently indicate
most likely rain totals by late Monday of 0.25 to 0.50 inches. Warm
advection ahead of an approaching warm front could support
lingering low clouds and spotty showers into Tuesday.

Temperatures could potentially spike well into the 50s Tuesday,
if the region breaks into the warm sector ahead of an upstream
cold front. The chance of showers will ramp up ahead of the
approaching cold front Tuesday night into Wed.

&&

.AVIATION /09Z WEDNESDAY THROUGH SUNDAY/...
Widespread snow showers have ended, for the time being.
However, cigs at both KBFD and KJST will remain MVFR overnight,
with borderline MVFR/VFR cigs at AOO and UNV. Elsewhere,
predominantly VFR conds are expected overnight.

Clouds will thicken from west to east on Wednesday as a cold
front approaches from the Midwest, with patchy light snow
developing across western PA later in the day.

The cold front will cross the airspace Wed night, accompanied
by snow showers (possibly mixed with rain across SE PA). This
front will usher in a reinforcing shot of cold air along with
blustery W/NW winds for Thursday that could gust 30-45 kts.
Scattered snow showers and restrictions will continue to impact
primarily northern/western PA (KBFD/KJST) on Thursday as well.

Outlook...

Fri-Sat...IFR/MVFR most likely at KBFD/KJST in scattered lake
effect and upslope snow showers. MVFR to low VFR expected
elsewhere. Decreasing W/NW winds.

Sun...Becoming VFR, with a light southerly breeze developing.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Lake Effect Snow Warning from 4 PM this afternoon to 8 PM EST
Friday for PAZ004>006-010-011.
Wind Advisory from 1 AM to 7 PM EST Thursday for PAZ004>006-
010>012-017>019-024>028-033>037-041-042-045-046-049>053-
056>059-063>066.
Winter Storm Warning from 4 PM this afternoon to 8 AM EST
Friday for PAZ017-024-033.

&&

$$

SYNOPSIS...Steinbugl
NEAR TERM...Fitzgerald
SHORT TERM...Fitzgerald/Steinbugl
LONG TERM...Fitzgerald/Colbert
AVIATION...Gartner/Evanego