PBZ issues Area Forecast Discussion (AFD) at Nov 27, 5:07 AM EST
782
FXUS61 KPBZ 271007
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
507 AM EST Wed Nov 27 2024
.SYNOPSIS...
Rain and snow returns tonight through through Thanksgiving. High
confidence in a colder pattern with occasional snow showers Friday
through early next week.
&&
.NEAR TERM /THROUGH TONIGHT/...
KEY MESSAGES:
- Seasonable temperatures and dry through the afternoon,
followed by rain and snow returning tonight.
------------------------------------------------------------------
Dry weather, seasonable temperatures, and increasing high clouds
are expected through the first half of today as surface high
pressure builds eastward across the area beneath quasi-zonal
flow aloft. The surface high pushes off to the east as an upper
trough approaches from the west this evening into tonight. Large
scale ascent strengthens over the local area between the downstream
trough and an upper ridge building over the eastern seaboard in
response. This will support widespread rain and snow spreading
west to east across the area, with most guidance (75%) continuing
to show precipitation beginning after 7pm. Any initial precipitation
is expected to wet-bulb thermal profiles, saturating and cooling
the column, taking temperatures down into the 30s and low 40s.
Most ensembles take the surface low track across the state of
West Virginia, but there is still track uncertainty that will
contribute to precipitation type uncertainty on the north side
of the low. Should the system pass farther south, snow chances
would be a bit higher across the northern half of the local area.
However, cold air will be hard to come by with relatively mild
upstream low-level temperatures leading to only weak (if any)
cold air advection. As of now, expecting the most likely
scenario to be one where snow mixes with rain primarily north of
Pittsburgh, with marginal thermodynamic profiles, low snow-to-
liquid ratios, and a mixed rain/snow precip type combining to
limit snowfall accumulation to a quick coating (perhaps up to
an inch in spots) of heavy, wet snow on grassy and elevated
surfaces (greatest chance of this occurring is north of I-80).
&&
.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
KEY MESSAGES:
- Rain and snow taper off by Thursday afternoon, though showers
may continue over the ridges and north of I-80 through
Thursday night. Only light additional accumulations are expected
in areas that see snow.
-------------------------------------------------------------------
The widespread precipitation departs to the east during morning
hours on Thanksgiving, with only some lingering showers over
the higher elevations and north of I-80 possible by dinnertime.
These showers, starting as a rain/snow mix then transitioning
to all snow overnight, could bring additional light accumulation
up to an an inch or so in the highest ridges and across the
northern half of Mercer/Venango/Forest counties, aided by
temperatures dropping below freezing due to cold advection.
&&
.LONG TERM /FRIDAY THROUGH TUESDAY/...
KEY MESSAGES:
- A pattern change ushers in much cooler temperatures beginning
Friday with occasional snow shower chances through the
weekend.
-------------------------------------------------------------------
The long term will be defined by an eastern trough with a
stacked low sitting on the southern periphery of the Hudson Bay.
Temperatures will remain below normal with high confidence
beginning Friday through at least the middle of next week, with
some uncertainty on when the trough will drift east thereafter.
Cold air aloft will force lapse rates to be close to dry-
adiabatic off the surface, even with surface temperatures as
much as 10 to 15 degrees below normal. There is still a roughly
70% chance of below freezing daytime highs Saturday through at
least next Tuesday. Local weather will be governed by the
intensity and timing of a series of shortwaves as they pivot
around the low.
The first of such shortwaves is progged to rotate through on
Friday. Current guidance suggests this wave may be timed well
with daytime heating to support convective snow showers during
the daytime. Combine this with the 20-30 degree thermal contrast
between the lake-land interface, this may warrant watching as a
day for snow squall concerns. Looking forward, the weekend may
see a temporary reprieve from shortwave effects, with snow
chances mostly confined to the lake-shore with some possibility
for snow showers sneaking into the northernmost portions of
Mercer/Venango/Forest counties. Confidence in shortwave timing
and intensity begins to break down early next week, though the
next signal for snow chances across a larger portion of the
local area appears to occur during the day Monday. The forecast
will need to be monitored for updates.
&&
.AVIATION /10Z WEDNESDAY THROUGH SUNDAY/...
Surface high pressure transiting overhead Wednesday will
maintain VFR conditions through most of the daytime hours. BKN
to OVC cirrus will stream through the area with increasing upper
level moisture ahead of our next system that will arrive
tonight. Light southwesterly wind will back to the east this
afternoon as the center of high pressure shifts to southeast of
the area.
Eventual degradation to MVFR and lower with showers is expected
after 00z Thursday with arrival of precipitation. Initially at
precip onset, which most likely ensemble timing pegs around 03z
for ZZV, 04z for PIT, and 06z for LBE (with still an hour or two
of wiggle room in either direction, more likely to lean later
given antecedent dry low-levels), a period of wet-bulbing may
result in some wet snow and locally lower visibility with
highest probability at FKL/DUJ. Elsewhere, precip type should
remain rain with temperatures staying warm enough. Eventually,
as the column saturates, conditions will deteriorate to IFR with
a 70-90% chance in the overnight hours and remain there with
improvement to VIS by Thursday morning. CIG restrictions appear
likely to continue with remnant moisture and strong low-level
cold advection supported by 80+% MVFR probabilities.
Outlook...
Periodic restrictions with rain and snow will likely continue
into the weekend with rounds of upper level waves invigorating
rain and snow showers. There is a chance for some banded snow
to develop on Friday which may result in brief, but impactful,
effects to terminals primarily from PIT and north.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...Cermak/Milcarek
NEAR TERM...Cermak
SHORT TERM...Cermak
LONG TERM...Cermak/Milcarek
AVIATION...MLB
Source: PBZ issues Area Forecast Discussion (AFD) at Nov 27, 5:07 AM EST (https://mesonet.agron.iastate.edu/p.php?pid=202411271007-KPBZ-FXUS61-AFDPBZ)
---------------
If I'm using your data in a way that is against your terms please email the team at "threatweb@pupswoof117.com"! I am a bot who will not respond in the comments at all and is only designed to post RSS feeds!