Area Forecast Discussion
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FXUS61 KPBZ 110419 AAC

Area Forecast Discussion...UPDATED
National Weather Service Pittsburgh PA
1119 PM EST Sun Dec 10 2017

Cold temperatures and periodic snow chances can be expected for
the coming week.


No substantive changes needed overnight, although the gradient
in PoPs has been sharpened to focus higher PoPs across the I-80
corridor. Any light snow showers in this vicinity should amount
to no more than a light dusting, although most areas are not
likely to see any meaningful accumulation. Previous discussion

A shortwave trough is moving sewd from the Great Lakes into the
upper Ohio Valley Region as it digs toward the base of the
entrenched ern CONUS trough. That disturbance may spawn some
light snow, and some eventual snow showers with overnight
passage. Accumulation will be minimal as broad ascent and mid-
level moisture with the system are very limited. In addition,
model soundings indicate moisture, wind and temperature
profiles remain unfavorable for snow growth in the cold flow in
its wake. Overnight minima will be slightly below average.


After a dry and slightly warmer Mon, the longwave trough that
has persisted over the northeast will deepen as a strong jet
core enters the backside of the trough. Light snow will develop
Monday night as moisture and lift increase ahead of an
approaching shortwave. A couple inches look likely across
northern zones closer to the surface low by daybreak...with
lesser amounts farther south. A second wave will quickly follow
on Tuesday...reinforcing the longwave trough and shifting the
trough axis east. This will set up strong cold air advection as
flow aloft turns to the northwest. Lapse rates and inversion
heights will increase quickly and allow for a long duration of
lake-effect snow potential across the I-80 corridor beginning
Tuesday through Wednesday.

Overall, minimal changes were made to the inherited forecast
and the potential for heavy snow across northern counties
remains, therefore, the Winter Storm Watch remains in effect
for Mon night through Wed.


An upstream shortwave is projected to back flow to the west on
Wednesday night, thus ending lake enhanced snow, before the reinforcing
front spawns more snow showers on Thursday, and initiates more
cold for Friday. Thereafter, another upstream trough is projected
to flatten flow and moderate temperature briefly back toward
the averages before cold frontral passage drops them again for
the start of the new week.


Condition deterioration to MVFR, with lcl IFR in shsn, is expected
as a shortwave crosses the region tonight. Confidence in that
IFR visibility potential is relatively low given the lack of
progged moisture and lift with this system.

Southwest wind will briefly veer westerly before shifting back
to the SW tomorrow in advance of a more potent system, progged
for Mon night.

Widespread restrictions will come with low pressure forecast for
Monday night/Tuesday with restrictions continuing through midweek.


PA...Winter Storm Watch from Monday evening through Wednesday
     afternoon for PAZ007>009-015-016.



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