Scientific Forecaster Discussion
fxus61 kpbz 130247
Area forecast discussion
National Weather Service Pittsburgh PA
947 PM EST Tue Dec 12 2017
bitter cold through wind chills through Wednesday. A Few Lake-
effect snow bands will bring localized accumulating snow
overnight with a more widespread snow event expected to bring
several inches to the region Wednesday afternoon into Wednesday
Near term /until 6 am Wednesday morning/...
snow showers continue but are weakening dry Arctic air continues
to stream in under northwesterly flow. Cloud coverage also
starting to show some breaks. With that...have opted to drop the
winter weather advisories from Indiana County South.
Jefferson/Clarion/Forest/Venango/Mercer will keep their
respective warnings/advisories with a possible narrow Huron
fetch developing as low pressure continues east, flow becomes
more favorable and inversion heights stay high enough overnight.
Models have remained fairly consistent in hinting at this
feature. Accumulations not impacted by any banding will have
light additional accumulations.
Very cold wind chills will persist overnight as Arctic air
continues to spill southward and temps already in the single
digits across northern zones.
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 /03z Wednesday through Sunday/...
periods of moderate snow would result in IFR conditions along a
relatively narrow band impacting fkl/duj overnight if a Huron
snow band develops...but otherwise high MVFR to VFR is expected
as dry Arctic air moves in and snow development diminishes.
VFR through much of the day...before the next system cross the
region Wednesday night. Restrictions likely at all terminals.
next chance for restrictions is Friday into Saturday.
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.
Maryland...Wind Chill Advisory until 1 PM EST Wednesday for mdz001.
PA...Winter Weather Advisory until 1 PM EST Wednesday for paz007-
Lake effect snow warning until 1 PM EST Wednesday for paz008-