Area Forecast Discussion
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849
FXUS61 KPBZ 151228
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
728 AM EST Fri Dec 15 2017

.SYNOPSIS...
Cold with another round of snow showers expected this evening,
mostly north of Pittsburgh. Some temperature moderation is then
expected over the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Minor tweaking update for the morning hours, as the forecast
remains on track. First isolated snow showers will form on the
ridges, as mid-level cooling should allow cloud tops to cool
towards ideal dendritic growth values by late morning/midday.
More organized activity still on track to arrive mainly north of
Pittsburgh by late afternoon/evening, as noted below.
Temperatures in mostly decent shape.

Previous discussion...

The GOES-16 Simple Water Vapor RGB shows our next disturbance
quite well, currently entering southern Wisconsin. This wave
will cross the western Great Lakes today, deepening the upper-
level trough and surface low under favorable upper-level jet
dynamics. Although the system lacks deep moisture, it will
acquire some low-level moisture on its journey through the Great
Lake aggregate. Steepening lapse rates under mid-level cooling
will help fuel snow showers as they enter our northwestern zones
this evening. Most of this activity will stay north of
Pittsburgh and probably north of I-80, but there will be
potential for accumulating snow showers south to the PGH metro
area. Current timing would be after the evening rush. A quick
1-2" is possible across the northern tier of counties, with a
marked decrease expected traveling south.

Snow showers will likely taper down after the passage of this
wave near midnight tonight. However, a developing low-level jet
and an injection of mid-level moisture will allow for some re-
invigoration of snow showers Saturday morning. This evolution is
represented well in the bevy of high-res models at our disposal.
This activity will likely stay north of the developing mid-level
warmfront, or roughly north of Pittsburgh. Another inch or so
could be the result of these showers. All told, the roughly
24-30hr snow total will likely remain under Advisory levels,
with the northernmost counties the most likely to flirt with the
3" mark. Elsewhere, and inch or less is expected.

In addition to the snow, the aforementioned strengthening low-
level jet will bring wind gust to the ridges that could near
Wind Advisory levels tonight. Current forecast remains just
below the Advisory threshold, although this will need to be
monitored through today. Regardless, the increased wind
tonight will bring a bite to the already cold air in place. Wind
chills will commonly be in the low teens to single digits,
colder in the higher terrain.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY/...
Warm air advection begins in earnest Saturday afternoon as high
pressure builds into the region. This will quell any remaining
shower activity that survives through midday. High temperatures
may still be held below average values, especially further
north where clouds will hold a little longer, but temperatures
will certainly be warmer than the previous couple of days.

High pressure will hold through Sunday morning, but another
disturbance will be knocking on our doorstep to end the weekend.
Isentropic lift along and just behind the lifting warmfront will
provide modest ascent as a weak upper-level wave moves into the
area. Will continue to carry chance PoPs for rain Sunday
evening. A little snow could mix in further north where
temperatures will be a few degrees cooler. No accumulation is
expected.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
A brief spell of zonal flow aloft will give way to
amplification once again heading into the middle of next week.
First, a trough will dig into the central CONUS Monday night
into Tuesday, bringing rain chances to the forecast area.
In the wake of this system, another brief spell of mostly dry
weather is expected Wednesday night into Thursday. Thereafter,
models have consistently shown another, strong system moving
through the eastern US late next week. Strong warm advection
ahead of this system should mean precipitation at onset would be
rain. Colder air is set to return next weekend.

&&

.AVIATION /13Z FRIDAY THROUGH TUESDAY/...
General VFR is expected through the day. Snow showers mainly
north of KPIT will develop night with the best chance of IFR at
KFKL/KDUJ. Analogs put the chance of LIFR at these ports
between 40 and 50%.


 Snow is expected at FKL and
possibly at DUJ Friday afternoon with visibility restrictions.

.Outlook...
Next chance for restrictions is late Friday into Saturday.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...None.
OH...None.
PA...None.
WV...None.

&&

$$



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