936
FXUS61 KPBZ 050154
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
854 PM EST Wed Dec 4 2024

.SYNOPSIS...
A strong low pressure system will bring winter weather impacts
across the region starting tonight. Snow squalls, strong winds,
and blowing snow are expected Thursday. Lake effect snow is
expected north of Pittsburgh into early Friday. Warmer weather
is expected over the weekend.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
KEY MESSAGES:

- Gusty winds through Thursday
- Intense snow bands/squalls are possible overnight (12am to 5am)
-------------------------------------------------------------

The forecast remains on track. Snow has been observed across
most of the area, with coverage expected to increase this
overnight. The strongest frontogenesis along the arctic front
is still "most likely" to pass through eastern Ohio in the
midnight to 2am timeframe, and across the rest of the area
generally between 2am and 4am.

Road temperatures are already around or below freezing along and
north of I-80 which will be conducive to immediate accumulation
of and snowfall. This has already been observed via public
reports and webcams and will continue in the I-80 corridor.
Towards the Pittsburgh metro and points south, road temperatures
are currently a few degrees above freezing. This may result in a
flash freeze; initial mixed precipitation or snow melts on road
surfaces before freezing behind the arctic front.

Strong frontogenesis along the cold front in marginally unstable
profiles with strong lift into the DGZ will lead to an intense
burst of snow, with 1"/hr rates or higher likely for a short
period of time. Towards the ridges, with orographic influence,
these rates may be as high as 2"/hr. This will bring rapid
deterioration of roadways with low visibilities and wind gusts
between 30mph and 40mph (localized white out conditions
possible). Travel will be very hazardous overnight.

Convective snow will also be possible behind the arctic front
with destabilizing profiles, but coverage is most likely to be
confined to the I-80 corridor with lake influence, with coverage
dropping off elsewhere by sunrise.

Because temperatures will fall drastically behind the front,
any icy road conditions will likely hang around through the
morning commute if not treated. Use extra caution if out on the
roads early Thursday morning.

.. Previous Discussion..

A deep trough, currently centered north of Minnesota this
afternoon, will continue to track east over the Great Lakes.
Warm advection into the afternoon will boost temps into the
mid/upper 30s through sunset under southwest flow south of
Pittsburgh.

Initially, light snow showers are possible between 8pm and
10pm. There may be a brief period of wintry mix with rain,
south of I-70 before the Arctic air overtakes the region by
midnight.

Robust snow showers/squalls increase in potential as a strong
cold front advances into eastern Ohio/western PA. Timing on snow
squalls will likely range between 12am to 4am; right before the
morning rush hour. A SPS (Special Weather Statement) was issued
to cover the lower elevations for the potential for snow squalls
through 15Z tomorrow. Snow Squall Warnings may be needed for
drivers before or during the morning rush hour.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY/...
KEY MESSAGES:

- Winter headlines remain in effect for portions of the area
  during this time period
- Wind chill values will be below zero in the higher terrain
  early Fri morning
-------------------------------------------------------------------

Widespread, synoptic snowfall will wind down after dawn
Thursday morning as winds begin to veer more westerly then
northwesterly. This will turn on the lake effect snow machine
that will persist through much of Friday for the I-80 corridor
and Erie snow belt. Snow storm totals north of I-80 may exceed
10-12 inches (40% probability) in select locations that see more
intense snow bands. A sharp drop-off in totals is expected to
the south of I-80, with locally higher amounts under more
persistent bands Thursday and Friday.

Given a strong pressure gradient with a potentially closed
upper-level low and passing 50-60kt LLJ, gusty winds are
expected to start this evening through Thursday. The potential
peak wind gusts are expected 5pm Wed through 4am Thurs. However,
lingering gusts may continue in the higher terrain due to
mountain wave activity. Advisory level winds are covered with
the Winter Hazard Products for the ridge locations; the Special
Weather Statement (SPS) also mentions the potential for 40mph to
45mph wind gusts for the lower elevations.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
KEY MESSAGES:

- Warmer weather is expected to return late week.
- Rain chances return Monday into Tuesday
-------------------------------------------------------------------

Snow showers are expected to taper off Friday night as the
trough exits and flow backs to the SW.

Building high pressure is expected to return warm temperatures
Sunday. Long range ensembles depict 40% grand ensemble
uncertainty when it comes to the strength of of the trough north
of New England that could impact how fast the cold air exits.

A majority of long range models shows a building trough west of
the Ohio River Valley late Monday into Tuesday. The probability
of measurable precipitation increases late Monday into Tuesday.
Currently, the likely range (noted in the 25th to 75th
percentile) shows precipitation amounts 0.25 to 0.65 inches for
a 24 hour total through early Tuesday. The potential for snow
Sunday through Tuesday is considered low (less than 5%) with
above average temps.

&&

.AVIATION /02Z THURSDAY THROUGH MONDAY/...
Warm advection-driven precipitation continues mainly north of
Pittsburgh as of this writing, mostly now in the form of snow.
This precipitation will start to become more widespread later
this evening ahead of an approaching cold front, generally with
continued MVFR/IFR visibility and slowly lowering ceilings. Wind
gusts have calmed slightly from earlier, generally in the 15-25
knot range at the moment.

IFR snow showers/MVFR ceilings will be more widespread by 03Z or
so. The passage of the cold front is still expected to provide a
round of heavier snow showers/snow squalls to the region
generally between 04Z and 09Z. Have used PROB30 groups at all
terminals to indicate the most-likely two hour window of impact
at each location. LIFR or perhaps VLIFR visibility can be
expected in these squalls, along with wind gusts in the 30-35
knot range.

Behind the front, snow shower coverage will drop off for
several terminals, with VCSH used. However, MVFR/IFR snow
showers will continue for airports susceptible to lake and/or
terrain effects, most notably FKL, DUJ, and LBE. Here, IFR or
low MVFR conditions will linger well into the daylight hours
Thursday, while MVFR to perhaps even low VFR ceilings develop at
other terminals by afternoon.

Windy conditions are expected to persist through the TAF period at
all terminals behind the front. Gusts to 30 knots are likely,
and may gust into the 35 to 40 knot range closer to the ridges.
Blowing snow may be a concern at locations north of I-80 and in
the ridges.

Outlook...
Improvement to VFR is expected from S-N Friday as the wave
exits and wind backs to the SW. Restriction and snow potential
could linger into Saturday for FKL/DUJ. Otherwise, VFR is
expected to prevail through Sunday before area-wide restrictions
again become possible Monday with rain.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Lake Effect Snow Warning until 1 PM EST Friday for PAZ007>009-
     015-016.
     Winter Weather Advisory until 7 AM EST Friday for PAZ013-014-
     022-077-078.
     Winter Storm Warning until 7 AM EST Friday for PAZ074-076.
OH...None.
WV...Winter Weather Advisory until 7 AM EST Friday for WVZ510-511.
     Winter Storm Warning until 7 AM EST Friday for WVZ512-513.
     Blizzard Warning until 7 AM EST Friday for WVZ514.

&&

$$

SYNOPSIS...Hefferan
NEAR TERM...Hefferan/Milcarek
SHORT TERM...Hefferan
LONG TERM...Hefferan
AVIATION...CL/AK