The Black Hills area of South Dakota can experience spectacular temperature variations. Day-to-day changes occur as cold and warm fronts cross the northern Plains. However, temperature ranges across the area at a given time can be just as great. They happen rapidly as the wind direction changes, most notably by the warming Chinook winds. Other temperature differences are caused by inversions, when warm air flows over a shallow pool of cold air. Because the Black Hills rise above the plains like an island in a body of water, they are in the warm air layer. The most notable temperature fluctuations occurred on January 22, 1943 when temperatures rose and fell almost 50 degrees in a few minutes. This phenomenon was caused when a frontal boundary separating extremely cold Arctic air from warmer Pacific air rolled like an ocean tide along the northern and eastern slopes of the Black Hills. In mid-January 1943, Arctic air pushed southward from Canada, bringing extremely cold temperatures across the central United States. By the morning of January 19, temperatures were well below zero as far south as Kansas and in the single digits to teens across Texas. On January 20, warmer air started to spread eastward from the Pacific over the Rockies while low temperatures ranged from -20 to -30 degrees across the Dakotas. The boundary separating this warmer air from the frigid air was near the front range of the Rocky Mountains and through Nebraska, with Casper WY at 22 degrees while Rapid City was -20 degrees. During the day, the warm air higher in the atmosphere reached the higher elevations of the Black Hills. Early morning temperatures on January 22 were already above freezing in the higher elevations of the Black Hills but still below zero along the foothills. Shortly after daybreak, the front moved northeast—down the slopes of the Black Hills—and temperatures warmed rapidly. Later in the morning, the front retreated to the southwest and temperatures plummeted just as quickly. The oscillations occurred several times during the morning; the front pushed east of Rapid City during the afternoon, allowing the airport to reach 50 degrees. It finally shifted south again during the late afternoon, and the cold air returned to the foothills. The change in temperature was noticeable as people rounded street corners. Motorists were unable to see out their windshields when thick frost formed as they encountered the front and plate glass windows cracked. Nearby Spearfish holds the world record for the fastest recorded temperature change. On January 22, 1943, at about 7:30 a.m., the temperature in Spearfish was −4 °F. The Chinook wind picked up speed rapidly, and two minutes later (7:32 a.m.) the temperature was +45 °F. The 49° rise in two minutes set a world record that still holds. By 9:00 a.m., the temperature had risen to 54 °F . Suddenly, the chinook died down and the temperature tumbled back to −4 °F . The 58 °F drop took only 27 minutes. The sudden change in temperatures caused glass windows to crack and shatter.  

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