On December 15, 2021, a rapidly-deepening low-pressure area contributed to a historic expanse of inclement weather across the Great Plains and Midwestern United States, resulting in an unprecedented[5] December derecho and tornado outbreak across portions of the Northern United States, a region normally affected by snow and cold weather during this time of year.

Non-thunderstorm winds spurred the formation of rapidly-moving fires across Colorado and western Kansas, with attendant dust and debris spreading eastward.

The culmination of non-thunderstorm, thunderstorm, and tornadic winds caused widespread damage to structures, trees, power lines, and vehicles across the Plains and Midwest.

At least 600,000 people lost power on December 15, and temperatures dropped significantly across the affected region following the event, causing accumulating snow, which hindered cleanup and recovery efforts.

[8] On December 15, the Storm Prediction Center (SPC) noted the potential for a widespread, damaging wind event across the Central United States.

[10] In Iowa, dew points surged to the upper 50s and lower 60s Fahrenheit, while convective available potential energy values – a measure of instability – were predicted to reach 500–1,000 J/kg.

Given these factors, in conjunction with an eroding capping inversion, forecasters expected a narrow but intense line of severe thunderstorms to develop and overspread the Mid-Missouri and Upper Mississippi valleys.

[12] The first tornado watch of the day was issued at 19:20 UTC and encompassed areas from northeastern Kansas northeastward into southern Minnesota as a rapidly-moving squall line developed.

[citation needed] The Colorado Department of Public Health and Environment enacted an Air Quality Alert across the Front Range due to the expected combination of dirt and dust.

The annual Denver Christkindlmarket, a holiday market celebrating German tradition, and the nearby Monarch Mountain ski resort were closed.

The Colorado Springs Fire Department responded to a large gas line break at the Chapel Hills Mall and evacuated that structure.

This line of convection intensified as it moved rapidly northeastward,[28] reaching eastern Iowa and western Wisconsin by the end of the day.

[23] Strong winds of 94 mph (151 km/h) were reported near Junction City, where hangars were damaged at the airport, siding was ripped from buildings, and metal signs were bent.

Kansas Governor Laura Kelly issued an inclement weather declaration for Shawnee County, sending executive branch agency personnel home.

Widespread reports of toppled trees, overturned semi-trucks, downed power lines, and blown out vehicle windows were received by local authorities.

Lancaster County was principally hard hit, with structural damage to an apartment complex's roof; Lincoln Airport recorded a gust of 93 mph (150 km/h).

[31] In Iowa, where the Department of Transportation closed bridges and the United States Army Corps of Engineers restricted access to the Saylorville Lake Dam in preparation for the weather event, similarly destructive winds were observed.

Hundreds of reports of power outages filtered in across the state as widespread hurricane-force gusts were recorded,[32] reaching 88 mph (142 km/h) in Audubon.

[214] The storm brought a foot of snow to Salt Lake City by the morning of December 15,[215] and higher totals in the Wasatch Mountains, up to 21 inches (53 cm) in Snowbird.