PBZ issues Area Forecast Discussion (AFD) at Dec 13, 8:41 AM EST244
FXUS61 KPBZ 131341
AFDPBZ
Area Forecast Discussion
National Weather Service Pittsburgh PA
841 AM EST Fri Dec 13 2024
.SYNOPSIS...
Dry conditions with a warming trend expected through Saturday.
A mix of ice and snow is possible Sunday morning, followed by
rain in the afternoon. Occasional rain chances with above
average temperatures next week.
&&
.NEAR TERM /THROUGH TONIGHT/...
KEY MESSAGES:
- Morning snow followed by clearing skies.
-------------------------------------------------------------
Some light snow continues across the area this morning aided by
mid-level jet entrance region dynamics and just enough moisture into
the dendritic growth zone as per our 12z sounding. Total
accumulations have been minimal and webcams don't indicate much
if any reduction to visibility. Expect the snow to depart in
the next hour or two as the forcing moves off to the east giving
way to a dry remainder of the day.
Subsidence is expected behind the weak wave and jetlet and
under an anomalous high pressure (+10 to 12dm). Upper ridging
and subsidence will gradually squash the saturated low/mid-level
cloud deck with surface mixing raises bases. Consequently,
clearing and increasing temperatures are expected into the day.
Despite anomalous heights, low level cold air will linger,
keeping temperatures 5 to 10 degrees below normal.
&&
.SHORT TERM /SATURDAY/...
KEY MESSAGES:
- Dry with increasing temperatures.
--------------------------------------------------------------------
Increasing warm air is expected to advect aloft from the
southwest throughout the short term. Despite this, decoupling
overnight is expected. Light to calm winds to drop lows around
10 degrees below normals, though wind chills will remain close
to temperatures.
Mixing into clear skies with more warm air aloft will push
temperatures near-to-above average Saturday with increasing high
clouds throughout the day. Dry weather continues with high
probability. Surface winds veer easterly in a cold air damming
setup on the east side of the Allegheny Front.
&&
.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
KEY MESSAGES:
- Low probability, moderate impact potential for light ice and
snow accumulations Sunday morning.
- Moderating temperatures into next week in an unsettled pattern.
--------------------------------------------------------------------
Ensemble clusters are in good agreement on a weak wave traversing
the central CONUS Saturday into Sunday fostering surface
cyclogenesis and weak low pressure sliding up through the Great
Lakes. This will introduce precipitation chances for our area.
Timing has trended slightly towards Sunday morning for the
highest chance of precipitation onset., though initial
precipitation will have to battle a lot of dry air at onset, wet
bulbing surface profiles.
In the last 12 hours or so, most ensemble clusters have come to
an agreement in timing and relative intensity. There is still
uncertainty in exacts with regard to precip type, but the
general thinking is that the areas that have the best chance to
see potential for freezing rain impacts are the I-80 corridor
and the Laurels down to WV ridges as the column saturates
(medium probability). This is due in part to 1) colder air
temperatures in place Saturday and Saturday night ahead of
precipitation and 2) for the ridges, southeasterly flow is
favored to persist behind departing high pressure. This setup
typically makes it tougher for cold air to erode in a warm
advection regime, and not near as quickly as the NBM wants it
to. Combine this with drying downslope effects and a wet-bulbing
scenario and this could help to keep near- surface temperatures
colder for longer. Regardless of ensemble flavor, elevated
probabilities for measurable ice increase Sunday morning,
highest in the ridges.
As for the lowlands and south of I-80, conditions will depend
on the exact onset of precipitation. Before sunrise, radiation
will not warm surfaces above freezing. After sunrise, roads will
warm in surface radiative processes, but limbs and branches may
be more reliant on air temperature. Lowland ice still remains
lower probability dependent on onset timing.
There is high confidence in the continuation of progressive flow
with weak embedded waves through early next week allowing rain
chances to continue. Clusters may wash out shortwave positioning
uncertainty which will affect exact precipitation chances, but
cluster means tend towards some weak eastern troughing by late-
week which may bring a slight cool down.
&&
.AVIATION /14Z FRIDAY THROUGH TUESDAY/...
Light snow in eastern Ohio and southwestern Pennsylvania is
expected to move out of the area by mid-morning. Majority of the
terminals are VFR with LBE at MVFR. Once the snow moves out of
the area, ceilings are expected to gradually rise throughout the
day. Expect cirrus this afternoon. Winds expect to remain around
5 knots veering from the northwest to the northeast by tomorrow
morning.
Outlook...
Restrictions are likely to return on Sunday with a new
disturbance and expected to persist through Monday morning.
&&
.PBZ WATCHES/WARNINGS/ADVISORIES...
PA...None.
OH...None.
WV...None.
&&
$$
SYNOPSIS...Milcarek
NEAR TERM...MLB/Milcarek
SHORT TERM...Milcarek
LONG TERM...MLB/Milcarek
AVIATION...Lupo
Source:
PBZ issues Area Forecast Discussion (AFD) at Dec 13, 8:41 AM EST---------------
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