A shortwave trough on the backside of an extensive upper level trough brought several rounds of snow to southwest Idaho on December 30th to December 31st.
Every event with a place to put it; 5 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.
A shortwave trough on the backside of an extensive upper level trough brought several rounds of snow to southwest Idaho on December 30th to December 31st.
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 29, 2:05 PM MST, 1 hour 55 minutes earlier.
Area Forecast Discussion
National Weather Service Boise ID
205 PM MST Wed Dec 29 2021
.SHORT TERM...Tonight through Friday night...The widespread snow
event over the area this afternoon will shift south and weaken by
early this evening as a cold front ushers in drier air from the
north. There will be a period of clearing skies overnight which
will allow for colder temperatures early Thursday morning.
Another system in western Canada will move southward overnight and
reach our area on Thursday. Snow will arrive first in the north
early Wednesday morning and will spread into the Treasure Valley
west of Mountain Home by mid-morning. The snow will continue to
move into the remainder of the area during the afternoon. In
addition to the snow, gusty southwest winds across portions of
southeast Oregon and southwest Idaho (south of the Snake River
Plain) will lead to areas of blowing and drifting snow through
Thursday night. Snow will continue through Wednesday night,
mainly in the mountains, with the arrival of an upper trough.
Total snowfall amounts of up to 2 inches are expected in the lower
valleys (locally 3 along the foothills), 3 to 6 inches in the
mountain valleys (such as the Long Valley, Upper Weiser Basin),
and 6 inches or more in the mountains. Snow showers will linger on
Friday for additional light snowfall accumulations - mainly in
the mountains. The system will finally exit to the east Friday
night for decreasing clouds and winds, resulting in very cold
temperatures early Saturday morning.
.LONG TERM...Saturday through Wednesday...Arctic air from a deep
upper level low in Canada will bring temperatures 10-20 degrees
below normal through Saturday night. Overnight lows will be in the
single digits for the valleys, and below zero in the mountains. A
very gradual warming trend will begin Saturday night, as a ridge
builds in from the southwest. We expect dry, cold, and mostly
clear conditions through Sunday night. There is fairly good model
agreement on southwest flow aloft and an accompanying atmospheric
river moving into our region later on Monday. The NBM appears to
continue to be confused on temperature and precipitation type
agreement. This is probably due to model disagreement on
precipitation type outcomes for next week. The ECMWF model favors
a rain-snow mix, shifting towards warmer temperatures for highs on
Monday, while the GFS is trending cooler showing mostly snow
during the day on Tuesday. Both models still show a sharp
temperature gradient with a cold frontal passage late Tuesday,
meaning a majority of the precipitation event will turn to snow
that night in the region. We will see widespread precipitation
continue into late Wednesday, as the trough moves to our east and
a warm front moves into the area with northwest flow aloft.
&&
.AVIATION...Widespread IFR/LIFR snow. Heaviest snow will be near
the West Central, Boise, and Owyhee Mountains. Mountains obscured.
Snow will end north of the Treasure Valley in the early evening
with the passage of a cold front. The Magic Valley will see
scattered snow showers until 30/02Z. Surface winds: SE-SW 5-10 kt
switching to W-NW Wednesday afternoon. Winds aloft at 10kft MSL:
NW-SW 20-35 kt.
&&
.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Winter Weather Advisory until 5 PM MST this afternoon
IDZ012>014-029.
OR...Winter Weather Advisory until 5 PM MST /4 PM PST/ this afternoon
ORZ063-064.
&&
www.weather.gov/Boise
www.facebook.com/NWSBoise
www.twitter.com/NWSBoise
SHORT TERM...BW
LONG TERM....SA
AVIATION.....SAPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BOISE ID
1026 AM MST WED DEC 29 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1020 AM SNOW 7 SSE NEW PLYMOUTH 43.87N 116.78W
12/29/2021 M4.0 INCH PAYETTE ID PUBLIC
MEASURED 4 INCHES IN SAND HOLLOW. STILL
SNOWING.
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BOISE ID
1238 PM MST WED DEC 29 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
1230 PM SNOW 3 SW EAGLE 43.66N 116.40W
12/29/2021 M2.5 INCH ADA ID NWS EMPLOYEE
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BOISE ID
104 PM MST WED DEC 29 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0800 AM SNOW 4 SSW DONNELLY 44.67N 116.12W
12/29/2021 M8.0 INCH VALLEY ID PUBLIC
TAMARACK SKI RESORT SNOW STAKE. TOTAL
SNOWFALL OVERNIGHT.
0700 AM SNOW CENTERVILLE 43.90N 115.90W
12/29/2021 M7.0 INCH BOISE ID COCORAHS
COCORAHS STATION ID-BS-10 PLACERVILLE 3.6
SE.
0700 AM SNOW GREENLEAF 43.67N 116.81W
12/29/2021 M4.0 INCH CANYON ID COCORAHS
COCORAHS STATION ID-CY-21 GREENLEAF 0.4 E.
0800 AM SNOW MCCALL 44.91N 116.10W
12/29/2021 M4.0 INCH VALLEY ID DEPT OF HIGHWAYS
TOTAL SNOWFALL OVERNIGHT.
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BOISE ID
215 PM MST WED DEC 29 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0210 PM SNOW GARDEN CITY 43.64N 116.24W
12/29/2021 M3.0 INCH ADA ID TRAINED SPOTTER
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BOISE ID
313 PM MST WED DEC 29 2021
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0312 PM SNOW STAR 43.70N 116.48W
12/29/2021 M4.0 INCH ADA ID BROADCAST MEDIA
&&The national radar mosaic for the moment the first event began.
5 heavy snow. Local standard time, as filed.
A member of the public measured 3.0 inches of snow in Nampa, ID.
A member of the public measured 3.0 inches of snow in Meridian, ID.
A CoCoRaHS station measured 11.5 inches of snow in Placerville, ID.
A CoCoRaHS station measured 6.0 inches of snow twelve miles northeast of Boise, ID.
A CoCoRaHS station measured 4.5 inches of snow about eleven miles northwest of Mountain Home, 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: 999226, 999227, 999223, 999224, 999225.