English: An anomalous and historic December derecho—a windstorm associated with an unusually strong and fast-moving line of thunderstorms—swept from the U.S. Southwest to the Upper Midwest on December 15, 2021. High-wind warnings were issued from the Central and Southern High Plains to the Great Lakes, including storm warnings over the Great Lakes.

The storm brought hurricane-force winds, dust storms, tornadoes, wildfires, snow squalls, and heavy rain across the middle of the country. Hundreds of thousands of homes and businesses lost electric power, and roughly 100 million Americans were under some type of weather warning that day.

The Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Aqua satellite acquired a true-color image of the first part of the storm, on December 15, when strong winds kicked up a thick and widespread blanket of dust. At the time the image was captured, the dust covered parts of Texas, Colorado, Oklahoma, and Kansas, obscuring visibility on the ground and hiding the ground from view from space.

The derecho was spawned by the interaction of a deep-low pressure system over the Northern High Plains and a high-pressure system to the west. This created a tight pressure gradient over the Rocky Mountains that generated fierce winds. The storm generated at least 55 hurricane-force gusts (those exceeding 75 miles per hour), breaking the previous one-day record (since tracking began in 2004). All previous records were set during the summer months. According to the National Weather Service, a derecho is a widespread, long-lived wind storm that is associated with a band of rapidly moving showers or thunderstorms. If the wind damage swath extends more than 240 miles (about 400 km) and includes wind gust of at least 58 mph (93 km/h) or greater along most of its length, then the event meets the classification of a derecho.

In Colorado, wind gusts exceeded 100 miles (160 kilometers) per hour and dust storms swirled in southeastern part of the state and in western Kansas. Snow and rain showers, along with at least 20 tornadoes, were reported along the squall line.

Meanwhile, ahead of the front, parts of the Southern Plains into the Upper Midwest saw record-breaking warm temperatures. In Wisconsin and Iowa, temperatures reached above 70 degrees Fahrenheit (21° Celsius). The heat and the high winds also prompted extreme fire weather warnings for parts of the Central and Southern Plains, as wildfires broke out in Kansas, Texas, and Oklahoma.