Images of a wild yet mild winter in the United States

December 2021 was one of the warmest wintertime months ever observed in the United States.

Regular intrusions of warm gulf air infiltrated the central and eastern United States, leading to a month that felt far more like spring than winter. The above image displays county zones where the temperature approached or exceeded record highs. A vast majority of counties east of the Rockies recorded temperatures far above average.

A devastating tornado: Dec. 11

Amid the unusual wintertime warmth, more tornadoes occurred in the United States than in any other December on record. One chapter of this very unusual activity was a powerful storm system that incited a number of intense and deadly tornadoes over the Mid-South on Dec. 10, including a particularly powerful and long-lived tornado that devastated a swath of Kentucky.

A radar image taken moments before the tornado tore through the community of Mayfield, Ky., shows a defined debris ball, a pink circle of very strong returns indicating wreckage lofted high into the atmosphere.

The Colorado inferno: Dec. 30

An unusual lack of early-winter snow combined with persistent drought conditions in portions of Colorado, contributing to regional susceptibility to wildfires — typically a summertime threat — at the beginning of winter. On Dec. 30, as an impressive windstorm swept across the Rocky Mountains, a violent grass fire rapidly engulfed suburbs northwest of Denver to become the most destructive inferno in Colorado history.

A radar image from that evening shows the thick plume of low-level smoke, less than a dozen miles north of the Denver radar site, that developed as the fire destroyed approximately 1,000 homes.

A two-week December deluge

A pattern exceptionally favorable for the development of atmospheric rivers—the type of storm that delivers much of the West Coast’s precipitation—remained stuck over the Pacific in the middle of December. Three weeks of seemingly endless rain and snow battered the West, especially California’s Sierra Nevada.

The deluge partially replenished reservoirs and the snowpack and brought hope of a winter that could continue to alleviate deep drought conditions. Two to five times the normal December rain and snow fell over the course of the month.

… and two parched months—January and February

Optimism generated by a very wet December was quickly dashed by two of the driest winter months in California history. An expansive zone of mid-atmospheric high pressure prohibited even light showers from reaching much of the West for the entirety of January and February, typically the region’s two wettest months.

By March 1, two-month precipitation totals revealed almost no rain or snow accumulated anywhere in California, an astonishing deviation from normal that all but assures the state ends yet another wet season with below-average precipitation.

Boston bomb cyclone and blizzard: Jan. 28

A powerful nor’easter brought very heavy snow to parts of the Northeast at the end of January, with a slow-moving band dropping accumulations that neared or even exceeded single-day records in cities including Boston, Providence and Islip. Boston posted 23.6 inches of snow on Jan. 28.

As the atmospheric pressure of a storm decreases, its intensity tends to increase, and the late-January nor’easter exhibited unusually rapid falls in pressure. In just 24 hours, the storm’s central pressure fell by an astonishing 38 millibars, a drop depicted in these images of the nor’easter at 2 pm on Jan. 27 and 28. The pressure decrease was almost double the 24 millibars in 24 hours needed for the storm to be considered a bomb cyclone.

Cross-country storm: Feb. 2-4

A major early-February winter storm dropped an expansive swath of snow from the southern Rocky Mountains to Maine, with significant accumulations that exceeded six inches in 16 states. The storm was associated with one of the widest winter storm warning events in US history, and more than 5,000 airline flights were canceled on Feb. 3. An image of snowfall accumulation across the country shows the vast area of ​​heavy snowfall.

An outbreak of very cold air spilled into the central and western United States at the end of February, setting dozens of daily records from Southern California to the Dakotas. The reach and magnitude of cold air is evident in a Feb. 23 infrared satellite image, which measures temperature from orbit. The Central Plains and interior Canada are colored blue, because ground temperatures in these areas are in the range often detected atop mid-atmospheric clouds in satellite measurements.

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