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fxus61 kpbz 122233 
afdpbz

Area forecast discussion
National Weather Service Pittsburgh PA
533 PM EST Tue Dec 12 2017

Synopsis...
sharply colder temperatures and bitterly cold wind chills
expected through Wednesday. A Few Lake-effect snow bands will
bring localized accumulating snow, with a more widespread snow
event expected to bring several inches to the region Wednesday
afternoon into Wednesday night.

&&

Near term /until 6 am Wednesday morning/...
light, but numerous convective snow showers continue to dust
the area, with a more singular thin band extending from
Cleveland to Moon Township/Pittsburgh with traces back to Lake
Michigan. Overall, the threat of accumulating snow through
tonight has largely diminished as temperatures are now in the
teens with dewpoints already in the single digits limiting the
extent of deep moisture.

Overnight, hi-res convective models vary on the degree to which
additional lake-effect bands will form. With these fast moving
clippers, flow trajectories are not stagnant to develop
persistent bands across the Narrow Lake fetch given the overall
wind direction. Let the lake- effect snow warning ride up north
for now, given some of the convective allowing output, but
really think that a couple inches across the rural north will be
more common than an isolated 4-6" additional amount beyond
what's fallen.

Outside of these extremely narrow snow bands, the main headline
overnight will be with bitterly cold wind chills. Arctic air
continues to spill southward with temps bottoming out overnight
in the low to mid teens, which should push wind chills down in
the 0 to -5 degree range most areas (colder WV mountains).

&&

Short term /6 am Wednesday morning through Thursday/...
after a brief break tomorrow morning, strong warm air advection aloft will
quickly overspread the area during the afternoon ahead of
another clipper - this one a bit further south than its
predecessor with a progged surface low track along I-70. Areas
along and north of the surface low should see a steady light to
moderate snow beginning Wed afternoon and continuing overnight.
Despite the Canadian origins of this wave, substantial large
scale isentropic ascent and sufficient Pacific moisture should
yield a widespread 2-4" snow event for the affected areas. Will
almost certainly need a Winter Weather Advisory headline, but
after collaboration did not want to confuse the ongoing
headlines with the second event, so have held off for now.

Winds will once again become quite gusty across the Laurel
Highlands into the WV/Maryland mountains late Wednesday night as
classic Post-frontal isobar stacking occurs west of the
mountains. Could see gusts again over the 30 mph for a several
hour window around 12z Thursday.

&&

Long term /Thursday night through Tuesday/...
brief cold advection follows behind the departure of Wednesday
night/thursday's system. This will be short-lived, however, as a
general retrogression of the upper trough toward the High Plains
seems in store for next weekend. This will result in more normal
temperatures returning to the region, but with the threat of a
southern jet branch storm that should bring primarily rain
across the area on Sunday.

&&

Aviation /22z Tuesday through Sunday/...
periods of moderate snow will result in intermittent IFR
conditions along a relatively narrow band of snow impacting
bvi-pit-agc-lbe. General MVFR with scattered show showers
elsewhere.

General MVFR conditions with scattered light snow IFR expected
during periods of moderate snow...mainly along a relatively
narrow band of snow impacting bvi-pit-agc-lbe

Expect some improvement later today outside of the terminals
impacted by lake-enhanced snow but general MVFR should prevail.

Flow will swing to the WNW with gusts to near 30kts.



Outlook...
periodic restrictions in snow showers and northwest flow will
continue through Wednesday. Another system will bring more snow
and restrictions to many of the terminals Thursday.

&&

Pbz watches/warnings/advisories...
Maryland...Winter Weather Advisory until 7 am EST Wednesday for mdz001.
Wind Chill Advisory until 1 PM EST Wednesday for mdz001.
Ohio...none.
PA...Winter Weather Advisory until 1 PM EST Wednesday for paz007-
016.
Lake effect snow warning until 1 PM EST Wednesday for paz008-
009-015.
Winter Weather Advisory until 7 am EST Wednesday for paz023-
074-076.
WV...Winter Weather Advisory until 7 am EST Wednesday for
wvz510>514.

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