Winter Storm and Heavy Snow in Idaho, December 1 to 2, 2022

Area Forecast Discussion
National Weather Service Pocatello ID
239 PM MST Wed Nov 30 2022

.SHORT TERM (Tonight - Friday AM)...
A period of active winter weather is underway across eastern Idaho
this afternoon and this will continue for the next 48 hours or so.
A strong area of low pressure off of British Columbia and its
associated moisture will overspread the region over the next few
days bringing widespread snow and gusty winds. Starting with the
snow, the next few days will bring FEET of snow to the Wood River
Valley north to Stanley and north of Ashton through Island Park
with up to around 2 feet of snow in the valleys and amounts up to
4 feet of snow in the mountains. Highest totals will be across
southern upslope favored areas of the Sawtooths, Western Smokys,
and Centennials. Totals across the eastern and southeastern
Highlands won't be nearly as high but still likely to reach around
a foot, or a bit more. Winter storm warnings continue for these
areas and we're expecting SIGNIFICANT impacts in these areas not
only from snow, but gusty winds creating widespread
blowing/drifting snow making travel extremely difficult in these
areas.

Elsewhere, Winter Weather Advisories are now in effect for the
rest of the area, including into the Snake Plain and eastern
Magic Valley. In those areas, accumulations are a bit more
difficult to forecast as southerly winds will likely allow for
temps to warm above freezing for a brief period, perhaps allowing
for a rain/snow mix during the afternoon hours. That being said,
hi-res model soundings show this layer as being very shallow or
non-existent (depending on your model of choice) so that
complicates matters a bit. Nevertheless, by late evening as the
front moves through, confidence is high that precip will be all
snow at this point and it will likely come down quite quickly with
the front. In addition to this, winds will be a concern as the
snow is falling creating some very difficult driving conditions
around much of the area and this will likely be during the evening
commute. For these reasons feel an advisory is the best course of
action for this event although totals will be on the low side
especially as you head into the eastern Magic Valley. Totals will
be higher however as you head towards AF and Pocatello and
especially from Blackfoot north on I-15. Totals across the Upper
Snake Plain, mainly from Rexburg into St. Anthony could flirt with
Winter Storm Warning criteria so an upgrade in this zone could be
needed on subsequent forecasts although Idaho Falls likely falls
in the 4-6" range for this event. In short, things are still a bit
in flux in spots but outside of the Snake Plain and Magic Valley,
there's good confidence in meeting advisory criteria.

Briefly discussed the wind concern already but late Thursday and
into Friday appears to be the time of biggest concern with winds.
Current wind forecast relies heavily on the NBM 90th percentile
and NBM 4.1 which has winds gusting in the 25-35 mph range for
much of the region with higher gusts expected in the higher
terrain and in the more wind-prone locations like near Yale and
Idahome.

Bottom line is this, expect a prolonged period of high-impact
winter weather across the region but the most significant impacts
will be focused across the Central Mountains and eastern
Highlands. Even if the current snow forecasts in the Snake Plain
don't quite materialize as they're currently forecast, winds will
still create winter weather impacts with the snow that does fall
and the snow that is currently on the ground across the region.
McKaughan

.LONG TERM (Friday through next Wednesday)...
This week's weather system will come to an end on Friday, but
we'll be dealing with some lingering snow east of Interstate 15
through Friday afternoon. We'll also be dealing with some gusty
winds throughout the day Friday in a post-cold frontal regime.
Weather will settle down Friday night with models depicting a
transient ridge shift through the area on Saturday. Deterministic
models indicate an upper low developing off the OR/CA coast
Saturday, pushing onshore on Sunday. As the low moves inland,
moisture will advect into Idaho from the south. Ensemble clusters
are still showing some uncertainty on when the upper low will fill
and eject eastward, a factor that will ultimately drive QPF for
the region. The 00Z EFI continues to maintain a relatively low-
impact weather system with no extreme snowfall, but anomalously
cooler temperatures. Quieter weather is indicated by most models
by Tuesday afternoon, but the region will remain at the backside
of a broad upper trough through Wednesday. Hinsberger

&&

.AVIATION...
Moisture continues to stream across southeast Idaho with snow
ongoing as SUN and DIJ. SUN remains below airfield minimums to
start off the TAF period, but NBM and HRRR guidance shows
improvements there by mid afternoon. DIJ has seen some bouts of
IFR visibility this morning, and NBM shows this to continue for a
couple more hours, but the terminal was VFR at TAF issuance. IDA
may see some periods of IFR visibility this afternoon with a band
of snow moving through, but PIH, IDA, and BYI should have a dry,
downslope wind through tonight. Conditions will again deteriorate
tonight as another batch of moisture is transported into the
region mostly impacting SUN and DIJ. Hinsberger

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 5 AM Thursday to 11 AM MST Friday
for IDZ051-052-068-070.

Winter Weather Advisory from 5 AM Thursday to 5 PM MST Friday
for IDZ053>059-061-062.

Winter Storm Warning from 5 AM Thursday to 5 PM MST Friday for
IDZ060-063>065.

Winter Storm Warning until 5 PM MST Friday for IDZ066.

Winter Storm Warning until 11 AM MST Friday for IDZ067-069.

Winter Storm Warning until 5 AM MST Friday for IDZ071>075.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE POCATELLO ID
1134 PM MST WED NOV 30 2022

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1247 PM     NON-TSTM WND GST 17 WSW MARION           42.17N 114.20W
11/30/2022  M46 MPH          CASSIA             ID   MESONET

            MESONET STATION CRII1 COTTON RIDGE.

&&

CM