Harrisburg, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

646
FXUS61 KCTP 031552
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1052 AM EST Tue Dec 3 2024

.SYNOPSIS...
* Cold and breezy conditions continue this week with
  temperatures below the historical average for early December
* Lake effect snow in Warren and McKean Counties shifts to the
  north tonight then ramps back up late Wednesday night-Friday
* Widespread snow showers and a few squalls are likely late
  Wednesday night into Thursday along with 30-50 mph wind gusts

&&

.NEAR TERM /UNTIL 7 PM THIS EVENING/...
Sfc trough axis tracking southward from the PA/NY border will
disrupt the heavier snow showers in the lake effect warning
area - but also help to deliver a broader area of mainly light
snow showers to the northern tier of CPA into midday. Hires
models suggest some mesoscale lake effect banding reestablishes
itself this afternoon extending southeast from Lake Erie [with
possible Huron connection] somewhere across the I80 corridor.
This may result in later adjustments to POPs, but for now we
added lower chances for snow showers/flurries through the
evening commute.

1540UTC GOES visible shows mostly sunny skies across the
majority of south central PA (outside of the Laurels) to the
south of the sfc trough axis. Arrival of slightly cooler air
aloft could lead to an uptick in stratocu into the afternoon and
latest trends would be generally supportive of increased cloud
cover particularly to the northwest of I81.

Daytime highs will be 5 to 10 degrees below the historical
average for early December ranging from the upper 20s in the
Allegheny Mtns to around 40F in the mid to lower Susquehanna
Valley.

For the Wed night-Thu sharp frontal system, we are considering
expanding the watch to include the Laurel Highlands later this
afternoon.

&&

.SHORT TERM /7 PM THIS EVENING THROUGH THURSDAY NIGHT/...
As the llvl wind finally pushes the LES to the N, the influence
of a major sfc low deepening over the Canadian Plains will
already be beginning. Clouds aloft will be brought in from the
west in the warm-ish advection in advance of the fronts
associated with the storm. Not much of a moisture inflow as the
low passes north of the Great Lakes, headed to srn Quebec by
Thursday aftn, deepening to 990mb as it does so. The tight
pressure gradient between the suppressed high and the vigorous
low will generate a strong/gusty wind, peaking Wed evening/night
(starting before CFROPA) and lasting into/through much of Thursday
(in the strong CAA). 60+KT winds get down to just 3-4kft Wed
evening at JST and 50+KT wind gets that low at BFD and much of
the rest of the area. But, there will be a 70-90deg veer to the
wind from the sfc to that level. After the front passes, Even
the lower elevation of the SE could get gusts well into the 40s
on Thursday when the vertical alignment gets better there. The
push of arctic air is a classic setup for widespread SHSN/SNSQ,
but timing of frontal passage is at the diurnal minimum, likely
before sunrise Thurs. The wind will probably require an advy ,
but the confidence is not quite there to hoist it on this shift.

The SHSN will amount to little before sunset Wed, but an inch or
less is a good bet for the Alleghenies by then. As the stronger
SHSN and front move through, a very accum could happen all the
way to Lancaster Co. But, the temps will actually be marginal
for any snow to stick. Have mentioned more a rain-snow mix for
them for later Wed night. After that, it`s all cold, but drying
out in the (Thurs) morning.

It`s the lake effect that will cause the most trouble in the Wed
PM-Thurs PM time frame. Expect another good Huron connection,
with a slightly north of west fetch. The possibility of 6+"
over the 36 hrs is high enough to post a watch for that time
frame. Elk county may be the beneficiary of the more-NWrly and
fast flow. We`ve added them to the watch along with Warren and
McKean. The Laurels may get 1-3 out of the first pass of snow
Wed/night, and another 1-3 on Thurs/night. This will probably be
enough for an advy, but there could be much of the day Thurs
where they will only have flurries. A very complicated
situation. The rest of the nrn mtns is on target to have 1-3",
and AOO-UNV in the 1-2" range, mostly Wed PM. Some point amounts
over 3" are possible, but the wind will be so strong that the
flakes may get fractured and blown around so much that it may
not be easy to get it to build up.

The SLRs waggle around thru the event, but will probably be near
20:1 during the heaviest lake effect time. So, even with gusts
into the 30s (N) and 40s (S) at times, the worry for power
outages due to snow on the power lines is low but more than
zero.

Temps may waggle up a little Wed night before the FROPA,
especially in the S. They will then fall, and stay steady or may
even continue to fall slightly through the day almost
everywhere. The clouds and well-mixed llvls Thursday night won`t
allow much of a temp fall. But, wind chills will be in the
single digits NW and teens SE. Spots in the Laurels may touch 0F
wind chills.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
A persistent upper-level trough will continue to allow for
cooler than average temperatures later this week and into the
weekend. High temperatures will remain 5-10F below normal
throughout much of the extended period with a notable exception
on Friday when a reinforcing shot of cold air moves into the
region. Cloud cover and breezy winds will make low temperatures
trend closer to seasonable averages; however, wind chills in the
single digits (and potentially below zero across portions of
the Laurel Highlands) throughout the weekend.

Ridging will begin building in Sunday, and height rises
combined with southerly flow could allow for moderating
temperatures for the beginning of next week. A warm front will
cross over Pennsylvania Sunday night into Monday associated
with a subtle shortwave. A mix of rain/snow/freezing rain could
be possible Sunday night into Monday given the current
temperature profiles, but this far out the system will continue
to be monitored for significant changes.

&&

.AVIATION /16Z TUESDAY THROUGH SATURDAY/...
Persistent lake effect snow showers will continue across BFD
vicinity through this afternoon before event winds down this
evening as snow showers become scattered. IFR cigs will
continue into tonight. Elsewhere, MVFR at AOO, JST and UNV,
generally from cigs will continue into this afternoon. IPT
should drop into MVFR also for several hours this morning as
another round of snow showers cross that region. MDT and LNS
should remain VFR, with maybe only a passing flurry.

Outlook...

Tue eve-Wed...Marginal improvement to MVFR/VFR across the NW
1/2 of the airspace.

Wed night-Thursday...Strong FROPA with widespread snow showers
and sharp wind shift with sfc gusts 30-45kt from 270-320 deg.

Fri-Sat...IFR/MVFR most likely at KBFD/KJST with return of lake
effect and upslope snow showers. MVFR to low VFR expected
elsewhere. Decreasing wind.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Lake Effect Snow Warning until 7 PM EST this evening for
PAZ004-005.
Winter Storm Watch from Wednesday afternoon through late
Thursday night for PAZ004-005-010.

&&

$$

SYNOPSIS...Steinbugl
NEAR TERM...Steinbugl
SHORT TERM...Dangelo
LONG TERM...DeVoir/NPB/Bowen
AVIATION...Martin/Gartner