An upper level low moved in from the northwest, bringing widespread mountain snow. Orographic lifting continued heavy snow from on December 11th through the 12th above 4,500 feet.
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 low moved in from the northwest, bringing widespread mountain snow. Orographic lifting continued heavy snow from on December 11th through the 12th above 4,500 feet.
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 11, 3:14 AM MST, 2 hours 16 minutes earlier.
Area Forecast Discussion
National Weather Service Boise ID
314 AM MST Sat Dec 11 2021
.SHORT TERM...Today through Monday night...As a significant upper
level low approaches the area from the northwest, snow will begin
to increase in coverage later this morning. Southwest flow aloft
will ramp up over the region, as well, providing favorable
orographic lift for the mountains of east-central Oregon and the
west-central Idaho mountains. Snow will then spread southwest-
ward throughout the day, eventually making its way into the Snake
Plain and the rest of southwest Idaho. Snow levels will be right
on the cusp of the Treasure Valley, and combined with SE winds at
the surface and mountain shadowing, the western Snake Plain will
struggle to receive much in the way of snowfall accumulations
compared to the Weiser Basin, Boise Mountains, west-central
Idaho, and portions of east-central Oregon. Snow levels will
gradually rise today, allowing lower elevations to transition to a
rain/snow mix or all rain by this afternoon/evening. Latest
ensemble guidance supports this transition, and suggests these
rising snow levels will continue for Sunday and Monday. Meanwhile,
moderate to heavy snowfall will persist over the mountains above
4000-5000 feet MSL, in addition to gusty southwesterly winds
throughout the period. This will result in dangerous travel
conditions for the mountains of southwest Idaho, particularly on
higher elevation corridors, as blowing and drifting snow will
restrict visibility and create roadway challenges. Winter weather
hazard products remain in effect through Tuesday.
LONG TERM...Monday through Saturday...Winter storm will continue to
bring widespread precipitation to the region through Tuesday.
Southwesterly flow will keep temperatures above normal and breezy
winds ahead of the upper level trough on Monday. Snow levels from
4500-5000 feet MSL will continue the heavy snow in the mountains
with valley rain. Southwestern facing slopes will see upslope
enhancements for increase snowfall totals in the Central and Boise
Mountains of Idaho, and the Wallowa Mountains of Oregon. Cold
frontal passage late Monday into Tuesday will lower snow levels to
the valley floors. Thus, precipitation could change over to snow at
all elevations. Please see our Winter Storm product for more
details. Colder temperatures and brief dry conditions expected
early Wednesday ahead of another upper level trough entering the
area on Thursday morning. Models in better agreement with
precipitation across much of the area Wednesday night into early
Thursday. Snow levels will remain at the valley floors and thus
snow is possible at all elevations. Colder airmass will remain in
place through the end of the week. Temperatures will be below
normal but could be significantly colder than currently forecast
if the valleys gets accumulating snow Wednesday/Thursday.
&&
.AVIATION...Scattered snow showers across Baker County Oregon and
the west central Idaho mountains this morning, becoming widespread
and expanding south to KBNO, KEUL, and KBOI by 18z Saturday,
reaching the Nevada border by 00z Sunday. Mixed precipitation is
possible at KONO, KEUL, KBOI and KMUO this afternoon. Areas of
mountain obscuration and local MVFR/IFR ceilings. Surface winds: E
to SW 10-20 kt with gusts up to 40 KTS across much of SE Oregon and
along the Idaho/Nevada border. Winds aloft at 10k feet MSL: W to NW
25-45 kt.
Sunday Outlook...Precipitation continuing, but decreasing to
isolated to scattered showers in the Snake River Valley and
southeast Oregon Sunday afternoon. Snow levels rising to around 4k
feet MSL BY 12Z/Sun and 5k feet MSL Sunday afternoon.
&&
.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Winter Storm Warning from 5 AM early this morning to 5 AM MST
Sunday IDZ033.
Winter Storm Warning from 5 AM early this morning to 11 PM MST
Tuesday IDZ011-013.
Winter Weather Advisory from 5 AM early this morning to 11 PM
MST Tuesday IDZ028.
OR...Winter Weather Advisory from 4 AM early this morning to 4 AM PST
Sunday ORZ062.
&&
www.weather.gov/Boise
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SHORT TERM...SH
LONG TERM....JS
AVIATION.....JSThe national radar mosaic for the moment the first event began.
12 heavy snow. Local standard time, as filed.
The Bogus Basin Ski snow stake webcam at 6,364 feet measured 13.0 inches of heavy snow with this system.
The Tamarack Ski Resort snow stake webcam at 6,600 feet measured 12.0 inches of heavy snow with this system.
The McCall town snow stake webcam at 6,600 feet measured 11.0 inches of heavy snow with this system.
The Brundage ski resort snow stake webcam at 6,600 feet measured 19.0 inches of heavy snow with this system.
The Mores Creek Summit NRCS SNOTEL measured 12.0 inches of snow at 6,100 feet.
The Deadwood Summit NRCS SNOTEL measured 17.0 inches of snow at 6,860 feet.
The Banner Summit NRCS SNOTEL measured 14.0 inches of snow at 7,040 feet.
The Bear Saddle SNOTEL measured 13.0 inches at 6,180 feet.
The Camas Creek Divide SNOTEL measured 6.0 inches of snow at 5,710 feet.
The Squaw Flat SNOTEL measured 16.0 inches of snow at 6,240 feet.
A member of the public reported a snow total of 12.0 inches in Fruitvale, ID.
The 24 hour report from a CoCoRaHS spotter was 8.6 inches.
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: 996629, 996632, 996682, 997447, 997469, 997524, 997523, 997527, 997529, 997533, 997535, 997536.