An upper level shortwave trough produced several snow bands in the region on December 27th-29th with the heaviest accumulations in the Upper Weiser Basin and the West Central Mountains.
Every event with a place to put it; 12 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS BOI wrote it up.
An upper level shortwave trough produced several snow bands in the region on December 27th-29th with the heaviest accumulations in the Upper Weiser Basin and the West Central Mountains.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Boise, ID wrote its last area forecast discussion before the first event at Dec 26, 3:27 AM MST, 3 hours 33 minutes earlier.
Area Forecast Discussion
National Weather Service Boise ID
327 AM MST Sun Dec 26 2021
.SHORT TERM...Today through Monday night...A deep upper trough
will continue to bring snow to our forecast area through Monday.
Snow showers will continue across the area today, with the best
chance of snow across the central Idaho mountains due to moist
southwest flow aloft. Winds today will be gusty, especially in the
higher terrain and areas south of the Snake River where gusts of
30-40 mph will occur. Areas of blowing snow will develop with
especially difficult travel conditions and low visibility.
Temperatures today will be about 5 degrees colder than yesterday
due to colder air arriving with the trough. A frontal boundary
will develop this afternoon across southern portions of the
forecast area, resulting in the formation of a band of snow in
these areas through Monday morning. Moderate to heavy snowfall
will occur within this band, and Winter Weather Advisories and
Winter Storm Warnings have been extended for southern portions of
our area through Monday afternoon. Gusty southwest winds will also
continue south of this frontal band before it shifts south into
northern Nevada by Monday afternoon. The upper trough axis will
finally swing across our area on Monday, ushering in a colder and
drier airmass. A chance of snow showers will continue into Monday
afternoon as the trough axis moves overhead before clearing
Monday night. Highs Monday will drop another 5 degrees from today,
with temperatures late Monday night dropping into the single
digits across many lower elevation locations, and below 0 in the
mountains.
LONG TERM...Tuesday through Sunday...Cold and dry northerly flow
will remain over the region through mid week with a broad area of
low pressure anchored to our northeast. Temperatures will continue
to be the coldest of the season thus far with highs in the 20s and
lows in the upper single digits...in the warmest locations. There is
agreement among the forecast models that a disturbance will slide
into the area from the north Thursday into Thursday Night in the
form of an arctic front. Moisture will be limited with the system,
but with cold air in place, the front could be a high efficiency
snow maker for the region. Any snow that falls would be high on the
powder scale. Another trough is expected to build off the coast late
in the week on into the weekend with ridging over the northern
Rockies making for dry and continued cold conditions. Anyone with
travel plans mid week should keep a close watch on the Thursday
system as details become clearer over the coming days.
&&
.AVIATION...VFR, except MVFR/IFR conditions in snow showers. Snow
showers will impact the terminals from KBOI/MYL southeastward to
KJER and KTWF overnight and into mid day Sunday. Showers will be
most numerous south and east of KBOI in the valleys, with mountain
locations seeing activity throughout. Mountains obscured. Surface
winds: SE-SW 5-15kt with gusts to 25kt becoming SW 10-20 kt with
gusts to 35 kt this afternoon. Winds aloft at 10kft MSL: W to SW 25-
45 kt.
&&
.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Winter Weather Advisory until 5 PM MST Monday IDZ016-028-030-033.
Winter Storm Warning until 5 PM MST Monday IDZ011-013-015-029.
OR...Winter Weather Advisory until 5 PM MST /4 PM PST/ Monday
ORZ061-063.
&&
www.weather.gov/Boise
www.facebook.com/NWSBoise
www.twitter.com/NWSBoise
SHORT TERM...ST
LONG TERM....MC
AVIATION.....MCThe national radar mosaic for the moment the first event began.
12 heavy snow. Local standard time, as filed.
A CoCoRaHS observer reported 3.5 inches of snow five miles southeast of Meridian, ID.
A CoCoRaHS observer measured 3.1 inches of snow three miles west of Garden City, ID.
A CoCoRaHS observer measured 3.0 inches of snow one mile north of Boise, ID.
A member of the public measured 4.0 inches of snow in Twin Falls, ID.
A NWS Employee reported 3.0 inches of snow in Kuna, ID.
A member of the public in Centerville, ID measured 6.0 inches of snow.
A CoCoRaHS observer reported 6.5 inches of snow 11 miles east northeast of Boise.
A CoCoRaHS site measured 4.0 inches of snow in Greenleaf, ID.
A CoCoRaHS site measured 3.8 inches of snow in New Meadows, ID.
A member of the public site measured 4.0 inches of snow in Sand Hollow, ID.
A NWS Employee measured 3.8 inches of snow north of Meridian, ID.
A NWS Employee measured 4.0 inches of snow south of Boise, ID.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Idaho in 2021Every state in 2021This day in weather historyWarnings in Idaho, December 2021
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 999196, 999205, 999207, 999208, 999194, 999209, 997771, 999212, 999218, 999220, 999221, 999222.