PBZ issues Area Forecast Discussion (AFD) at Nov 30, 1:13 PM EST900
FXUS61 KPBZ 301813
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
113 PM EST Sat Nov 30 2024
.SYNOPSIS...
Scattered snow showers are possible over the ridges this
morning. Otherwise cold temperatures will settle in for the long
haul. Another round of snow showers is possible Sunday and
Monday.
&&
.NEAR TERM /THROUGH SUNDAY/...
KEY MESSAGES:
- Well below normal temperatures tonight and tomorrow.
- Wind chills in the teens.
- Flurries ending this afternoon with some drying
- Snow for West Virginia ridges late tonight into Sunday
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Average Low/High for KPIT Sunday December 1st is 31/45, and we
will be running 10-15F below those values with 850 mb
temperatures staying in the -13 to -14C range.
Short wave ridge pushing into area is bringing drying trend with
clouds decreasing in Ohio. Batch of flurries moving SW to NE
should clear the area around sunset, so have accounted for this
based on rad/sat trends and the guidance progression of moisture
in the Dendrite Growth Zone which has captured things well
today.
Upstream short wave trough over MO has decent batch of warm
advection snows (best seen around 850 mb per SPC MesoAnalysis)
with it and those look on track to push through the far southern
part of area late tonight into Sunday, resulting in 1-3" snows
over the Preston/Tucker County WV area.
&&
.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
KEY MESSAGES:
- Well below normal temperatures with daily chances of snow
showers, mostly north and east of Pittsburgh.
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As the Quebec upper low wobbles it's way east, there is high
confidence it elongates, leaving a trough axis in its wake,
stretching from Labrador into the upper Great Lakes. This trough
will begin to feel the influence of its parent low through the day
Sunday, dropping southeast and bringing in a return of northwest
boundary layer flow through at least the middle of next week.
Surface cooling Sunday night combined with upper subsidence will act
to keep boundary layer lapse rates sub-dry-adiabatic, though
moisture trapped under a subsidence inversion in northwest flow will
advect a stratocumulus deck south through the night. Given the upper
forcing, low-level saturation, and a nearly 30 degree thermal
gradient between Lake Erie and northwest Pennsylvania, snow showers
could not be ruled out for most, but are expected to mostly be
confined to north of I-80 in the lake-effect belt, and perhaps the
ridges with orographic lift.
Chances of snow showers increase into Monday with daytime heating
destabilizing profiles. Combined with anomalously warm lake
temperatures, 850mb moisture should be prevalent to allow for
scattered to numerous snow showers downstream of Lake Erie as
convective temperatures are reached (Pittsburgh and points
north and east). Convective snow and near- freezing high
temperatures may result in some low- visibility and surface
accumulation periods in a relatively short span that may make
some travel difficult. Short-fuse, convective snow products may
be needed to cover the threat.
Monday night and Tuesday may see a similar fate as the day prior,
but shortwave forcing is less certain. The presence or timing of a
shortwave ridge or trough could make conditions less favorable or
similar respectively. Nonetheless, northwest flow and marginally
unstable to unstable profiles continue, meaning show chances remain
in the cards for now.
Storm total snowfall from northwest flow is expected to remain
limited but some areas see a better chance at accumulations than
others. For the Pittsburgh metro, there is a 90% chance of less than
an inch of accumulation at this time. Moving up to Oil City, there
is a 75% chance of greater than 1" of accumulation, but a 90% chance
of less than 3". Interestingly, however, there is a low probability
(5%) maxima of >6" which may represent whether a snow band is able to
maintain itself off of Erie. This remains low probability at
this time, given a sub-optimal WNW fetch. Hopping down to the
ridges, a gradual accumulation of a few inches is in the cards,
with around 80% of guidance below 3".
&&
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
KEY MESSAGES:
- Another disturbance arrives mid-week, with additional snow
chances, though forecast confidence still remains medium to
low.
-------------------------------------------------------------------
There is increasing confidence that a stacked low and reinforcing
cold shot arrives late week. Surface low positioning remains quite
uncertain with EPS, GEPS, and GEFS members; placement is centered in
between Lake Huron and the Hudson Bay by Thursday morning, with a
larger cluster of members favoring the southerly solution. A more
southern track would mean more forcing for snowfall, but exact
totals could be governed more by shortwave timing, which again, has
low predictability this far out.
At this time, the greatest probability of accumulation with the
system occurs Wednesday into Wednesday night. Chances of >3" of snow
are generally .50% northeast of the Pittsburgh metro and into the
ridges. There is a 30% chance of >6" in Jefferson (PA), Indiana,
Forest, and Clarion Counties. Additionally, the arctic front
may warrant watching for snow squall concerns.
Uncertainty increases drastically after this wave passes through as
some clustered ensemble attempt to reestablish ranging late week and
through the weekend, while other continue to allow eastern
troughing. The difference between these scenarios will drastically
affect the forecast. While both clusters favor below average
temperatures through the weekend, the key difference will be wind
direction. In ridging, winds back more westerly, removing lake
influence and with lower precipitation chances. Should troughing
continue, northwest flow could mean continued lake enhanced snow, in
the event that boundary layer flow orients 320 to 330 degrees, snow
banding is possible off of an optimal Huron/Erie fetch, which is
indicated by a sub-sect of long range guidance.
The CPC 6-10 day outlook maintains a 75% to 85% chance of below
average temperatures, while the 8-14 day outlook indicates a 60%
to 70% chance of below average temperatures, which could mean a
quite anomalously cool start to December, though the outlooks
leans slightly warm to close out the month.
&&
.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
MVFR to VFR Stratocumulus in place with batch of flurries moving
through the area that should end by evening. Significant drying
coming in from Ohio as a short wave ridge moves into region, and
could bring period of scattered clouds and VFR weather for
tonight and Sunday.
Batch of snow currently in MO will head for West Virginia late
tonight and early Sunday. Odds favor the restrictions and light
snow stay south of most of the TAF sites, but will be a close
call at KMGW and VFR with flurries is the most likely scenario
with IFR conditions staying just to the south.
Outlook...
Monday flow turns more northwest aloft and potential for Lake
Effect snow showers to move into northern half of area
increases, especially for KFKL and KDUJ where restrictions are
possible.
While flow remains northwest on Tuesday, rising heights and
subsidence may limit snow shower potential as compared to
Monday.
Low pressure moving across the Great Lakes Wednesday and into
Northeast Thursday likely to bring ceiling/visibility
restrictions and perhaps snow and gusty winds with highest
probabilities in the northern half of area.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...Milcarek
NEAR TERM...Craven
SHORT TERM...Milcarek
LONG TERM...Milcarek
AVIATION...Craven
Source:
PBZ issues Area Forecast Discussion (AFD) at Nov 30, 1:13 PM EST---------------
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