A low pressure system of historic strength led to a variety of high-end weather impacts from the central plains to the Upper Midwest and Great Lakes December 15-16. An unprecedented December severe weather unfolded over portions of Minnesota and Wisconsin Wednesday evening, with the Storm Prediction Center issuing their farthest-north Moderate Risk for the Month of December. A serial derecho moving at 60-70 mph tracked from Kansas to Wisconsin, resulting in over 400 reports of damaging wind and numerous tornadoes. Most of the damage across our area occurred from south-central Minnesota through west-central Wisconsin. The strongest tornado in west central Wisconsin hit Stanley.
Before the thunderstorms, strong southerly winds led to record high temperature at many sites across the Upper Midwest. Temperatures warmed into the mid to upper 50s across much of central Minnesota and western Wisconsin, and even exceeded 60 degrees across southern Minnesota. The warm temperatures melted what was left of the snowpack from the December 10 winter storm, which led to widespread dense fog through much of the morning and afternoon.
After the thunderstorms, strong gradient winds and widespread wind gusts in excess of 50 mph developed for several hours late Wednesday night and into the overnight hours. The Redwood Falls airport measured a gust of 78 mph at 11:30 PM.
Temperatures quickly fell below freezing across western and central Minnesota Wednesday night, causing rain to change over to a wintry mix of freezing drizzle and snow. Snowfall accumulations of 1-4 inches, along with the strong gusty winds, led to low visibility and travel hazards late Wednesday night into Thursday morning.

Tornado in EAU CLAIRE, WISCONSIN
From 15-DEC-21 21:00:00 to 15-DEC-21 21:06:00 (CST-6)
Location: FAIRCHILD
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

Mainly tree damage. Some trees fell on sheds, houses and vehicles. Two sheds had their roofs partially removed. Time estimated from radar.

Tornado in CHIPPEWA, WISCONSIN
From 15-DEC-21 21:16:00 to 15-DEC-21 21:22:00 (CST-6)
Location: BOYD
Tornado F-scale: EF2
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

This tornado first caused damage to groves of trees southwest of Stanley, then affected a couple farmsteads. It intensified significantly as it approached Stanley, demolishing an outbuilding and then two outbuildings with a construction business. An historic train depot had a portion of its roof removed. A high tension power line was blown down. About six homes had their roofs removed, and in the northeast edge of Stanley, a roof and outer walls were removed from a portion of a house. The tornado continued into northwestern Clark County where it damaged more trees and outbuildings (see entry from NWS La Crosse).

Tornado in CHIPPEWA, WISCONSIN
From 15-DEC-21 21:02:00 to 15-DEC-21 21:07:00 (CST-6)
Location: BATEMAN
Tornado F-scale: EF0
Property damage: 0.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

The tornado uprooted or broke hundreds of trees. Many trees landed on houses. Shingles were also removed from portions of two roofs. Soffits were torn away from three houses.

Thunderstorm Wind in PIERCE, WISCONSIN
From 15-DEC-21 20:15:00 to 15-DEC-21 20:18:00 (CST-6)
Location: DIAMOND BLUFF
Magnitude: 61.00 EG
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Emergency Manager

A outdoor weather siren on the east side of County Road 00 was damaged. Several trees were blown down and blocking roads from near Diamond Bluff to Ellsworth.

Thunderstorm Wind in PEPIN, WISCONSIN
From 15-DEC-21 20:10:00 to 15-DEC-21 20:15:00 (CST-6)
Location: STOCKHOLM
Magnitude: 56.00 EG
Property damage: 50.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Pepin County primarily had minor damages ��� trees down throughout the county, a couple of houses had minor roof damage, and one farm losing an agricultural structure that was only a year old.

Thunderstorm Wind in DUNN, WISCONSIN
From 15-DEC-21 20:44:00 to 15-DEC-21 20:49:00 (CST-6)
Location: (LUM)MENOMONIE AIRPORT
Magnitude: 52.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Some power outages noted east and north of Menomonie, along with isolated areas of trees blown down.