Heavy Snow in Idaho, December 22 to 23, 2017

Area Forecast Discussion
National Weather Service Pocatello ID
158 PM MST Fri Dec 22 2017

.SHORT TERM...Tonight through Christmas Night.

A strong cold front is approaching the region. We are beginning to
see snow break out across the region. Although light snow will be
possible across many areas tonight, the southeast Idaho highlands
will take the brunt of this first storm. Expect snow in the
southeast highlands to significantly pick up after 9pm this evening.
Amounts have increased across this region on the latest forecast
runs. It now looks like areas such as Lava Hot Springs, Soda
Springs, Preston and Montpelier could see up to 6 inches between
tonight and Saturday. Meanwhile, the passes could see up towards a
foot of new snow. We expect wind conditions as well, so blowing and
drifting snow will be a problem. Looks like we'll see a convergence
zone try to move down the Upper Snake Plain towards Idaho Falls,
Blackfoot, and Pocatello Saturday afternoon. However, winds will be
so strong, can't see it lingering and creating too many problems.
Still, an inch or so is possible with that during the afternoon.
Most areas outside of the southeast highlands will see a storm total
of 1 to 3 inches from this system. Expect a break Saturday night
into Sunday morning with cold temps likely during this time. By
Sunday afternoon, we'll see another storm system approach the area.
We expect to see snow overspread the region Sunday night and linger
into the eastern Idaho highlands on Christmas Day. Expect to see 1
to 3 inches across most places from Sunday afternoon through
Christmas Day. The exception is across the eastern Highlands from
Island Park through Driggs, Wayan, Lava Hot Springs, Soda Springs,
Preston and Montpelier could see 3 to 6 inches with an additional 6
to 12 inches possible at pass level. So, we could need an additional
winter weather advisory for Sunday and Christmas Day.

Valle

.LONG TERM...Tuesday through next Friday.  For Tuesday the GFS and
ECMWF models are in better agreement showing our area in Northwest
flow with moisture moving through the flow. The Sawtooths and
particularly the Eastern Highlands along the Wyoming border are the
favored areas for light to moderate snow. The ECMWF continues
moisture moving across our area through Friday in these areas. The
GFS model tapers off the moisture by late Thursday showing Friday
mostly dry. Expect near normal to slightly below normal temperatures
on Tuesday with slightly above normal temperatures Wednesday through
Friday. Wyatt

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.AVIATION...Winds are starting to become breezy and clouds are
continuing to drop across the area ahead of the next system. Look
for moisture to move through the area in Northwest flow. This system
should bring MVFR conditions by early evening for all TAF sites.
Heavier snow will start after midnight likely bringing IFR
conditions, particularly for KDIJ, KIDA, KPIH, and to a lesser
degree, KBYI and KSUN. Expect winds to remain breezy, if not
slightly increasing, overnight before picking up late tomorrow
morning into the afternoon as precipitation starts to taper off.
Blowing and drifting snow is expected impacting visibilities at
all TAF sites except maybe KSUN. IFR/MVFR CIGS will increase to
VFR for KSUN first by early to mid morning and lift for the
remaining sites by late morning to early afternoon. KIDA and KDIJ
may not become VFR until early to mid afternoon tomorrow. Wyatt

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.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 6 PM this evening to 6 PM MST
Saturday for IDZ023>025.

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