ST. LOUIS – January’s cold spell has made this month the coldest since 2011, but the much-needed January thaw is beginning to ramp up. A key factor driving this warm-up is the Chinook wind, which is common this time of year.

The Chinook wind is a warm, dry wind that originates in the Pacific Northwest, moving up into the mountains before descending rapidly down the eastern slopes of the Rocky Mountains. This descent causes the air to compress, warm, and dry, drastically raising temperatures in the northern and central plains.

On Tuesday, temperatures warmed 20 to 25 degrees above normal in the Upper Mississippi Valley. We reached 14 degrees above normal in St. Louis Tuesday with a high of 55 degrees.

The effects of the Chinook winds can be even more dramatic. In fact, the biggest recorded temperature jump occurred in Spearfish, South Dakota, on Jan. 22, 1943, when the temperature soared 49 degrees in just two minutes—from -4 degrees to 45 degrees. The January thaw is a welcome relief during the harsh winter months and is expected to continue through the Midwest until Wednesday.

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