284
FXUS61 KPBZ 221610
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
1110 AM EST Fri Nov 22 2024

.SYNOPSIS...
Low pressure just east of the region will maintain areas of
snow and rain today. The low will slowly exit the region
Saturday, with dry weather returning Sunday. Rain chances return
with a Monday cold front. A series of disturbances will bring unsettled
weather for much of the rest of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
KEY MESSAGES:

- Snow this morning, changing to rain outside of the higher
  terrain
- Significant snowfall expected across the higher terrain areas
------------------------------------------------------------------

Late Morning Update...
No changes to the forecast except to upgrade the Winter Storm
Warning in eastern Tucker County, WV to a Blizzard Warning,
which is now in effect until 10 AM EST Saturday. Hi-res ensemble
joint probabilities for visibilities below a quarter mile (due
to heavy, blowing snow) and wind gusts greater than 35 mph
hover in the 70-100% range this afternoon through tonight.
Travel through the higher elevations of northern WV will be
very dangerous during that time. Webcams already show road
conditions along I-68 in Preston County and Hwy 48 in Tucker
County rapidly deteriorating, with the heaviest snowfall rates
still to come later this evening.

Winter Storm Warnings remain in effect for the ridges of
Mon and Preston counties in WV, as well as the Laurel Highlands
in PA. The Winter Weather Advisory currently in effect until 1
PM this afternoon may need to be cancelled early, given the
transition from snow to rain that is occurring in lowland areas
at this time.

More information from previous AFD updates can be found
immediately below.

Early Morning Update...
Snow was spreading from N-S across the region this morning.
Adjusted the hourly POPs based on the recent radar and near term
model trends.

Previous discussion...
A large upper low was centered across southern PA and MD, while
a surface low was centered over southern New England. The
surface low will rotate around the upper low, and will be
located across eastern PA this afternoon and evening. A surface
trough extending west of the low was across southern Lake Erie,
and will be moving southward this morning.

Snow is expected to overspread the region from north to south
this morning as the surface trough moves south,and additional
moisture and ascent rotate around the upper low. A strengthening
low level jet should enhance this ascent through the day.
Critical thicknesses, 850mb temperatures, and model soundings
indicate the snow will mix with and change to rain from north to
south later this morning and afternoon. The exception will be
across the higher terrain areas, where the precipitation will
remain all snow.

A quick accumulation of snow is expected this morning as the
initial area of precip moves across the region. There should be
a relatively short window for accumulation, as temperatures
begin to rise and the snow mixes with and changes to rain.

A period of heavy snow is expected across the Laurel Highlands
and the higher terrain areas of WV. Maintained the Winter Storm
Warning in these locations through tonight/Saturday, with
advisories through early this afternoon just outside of the
higher terrain where lesser snow amounts are expected. Snowfall
rates of around 1 inch per hour are likely to develop across the
ridges, with wind gusts also increasing to between 40 and 50
mph. The increasing wind, and saturation in the dendritic growth
region, should lead to these efficient snowfall rates. One
limiting factor could be the warm advection aloft limiting lapse
rates, though the orographic lift component could cancel out
this effect.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
KEY MESSAGES:

- Winter storm in the ridges ends Saturday
- Rain/snow chances end by Sunday
-------------------------------------------------------------------

The low is progged to become vertically stacked tonight across
eastern PA. Rain will continue for much of the area as
additional moisture and jet supported ascent rotate around the
low. The ridges will remain all snow, and some snow could mix
back in with the rain near and east of a FKL-IDI line. Snowfall
rates across the ridges should begin to diminish this evening as
the depth of the moisture decreases, wnd saturation in the
dendritic layer lessens. Gusty wind will continue, especially
across the ridges, with the low level jet in place.

Rain and snow should gradually end Saturday as the low exits off
of the East Coast. Wind should also gradually diminish through
this period as the surface pressure gradient begins to relax.
There could be a period of freezing drizzle across the highest
terrain areas of Tucker county WV as the dendritic growth region
dries, but low level moisture remains.

Saturday night and Sunday should be dry with seasonable
temperatures as a ridge of high pressure builds in.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
KEY MESSAGES:

- Dry on Sunday
- Cold front returns Monday and Monday night
- Unsettled again, especially with a mid to late week low
-------------------------------------------------------------------

Model ensembles indicate flat ridging will be across the region
early Monday, ahead of an approaching Central CONUS trough.
Developing surface low pressure ahead of the trough is expected
to track from the Midwest to the Lower Great Lakes region later
Monday and Monday night, pulling a cold front across the area.
Rain chances will increase through the day, peaking Monday
evening/night with FROPA.

The upper trough axis will follow on Tuesday, with continued
rain and snow chances mainly north of PIT, where better lift and
moisture is progged. Ensembles then indicate a trough will
track across the Central CONUS on Wednesday, as a surface low
begins to develop across the TN/lower OH valley region.

Increasing moisture and lift in SW flow ahead of the trough will
return rain and snow chances to the area late Wednesday and
Wednesday night. Precipitation is likely by Thanksgiving as the
trough approaches, and the surface low tracks across the
TN/lower OH valley, and toward the Mid Atlantic coast. Rain and
snow are both possible, depending on the track of the surface
low, and amount of warm advection across the Upper Ohio Valley
region. With increased uncertainty in the exact scenario by
late week, stayed close to the ensemble blends for the forecast.

&&

.AVIATION /16Z FRIDAY THROUGH TUESDAY/...
A large-scale low pressure system will continue to impact
terminals over the next 24 hours. A surface low over New York
slowly tracks west through this morning, bringing another round
of light snow to area terminals (except ZZV) along with
widespread IFR cigs, with HREF probabilities showing a greater
than 70% chance for IFR at all TAF sites starting at 12Z.
Visibilities likewise drop to IFR due to precip (potentially
briefly LIFR in any heavier pockets). Snow transitions to rain
by mid to late morning, which could result in some minor
improvements in visibility to low-end MVFR, although terminals
closer to the ridges (DUJ/LBE/MGW) likely see snow, and
associated IFR visibilities, linger a bit longer into the day.

Wind gusts will also pick up this morning with improved mixing
and as the pressure gradient tightens in response to the
encroaching surface low; generally 20 to 30 knot westerly gusts
are likely at most terminals through the day.

Outlook...
Restrictions are expected through Saturday as low pressure
continues to spin over the NE CONUS, maintaining rain/snow
shower activity mostly across northeast OH, northwest PA, and
the ridges east of PIT/MGW. Elsewhere, precipitation begins to
taper off Saturday morning, though ceiling restrictions
persist. VFR should return Sunday as high pressure builds in.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...Winter Weather Advisory until 1 PM EST this afternoon for
     PAZ009-016-073-075-077-078.
     Winter Storm Warning until 7 AM EST Saturday for PAZ074-076.
OH...None.
WV...Winter Weather Advisory until 1 PM EST this afternoon for
     WVZ021-509.
     Winter Storm Warning until 7 AM EST Saturday for WVZ510>513.
     Blizzard Warning until 10 AM EST Saturday for WVZ514.

&&

$$

SYNOPSIS...WM
NEAR TERM...Cermak/WM
SHORT TERM...WM
LONG TERM...WM
AVIATION...Cermak/Hefferan