On January 22, 1943, the small town of Spearfish, South Dakota witnessed one of the most extraordinary temperature swings ever documented in meteorological history. Just before sunrise, residents woke to a bitter cold of –4°F, typical of a harsh winter morning in the northern Great Plains. But within moments, the town experienced a phenomenon so abrupt and powerful that it would later be recognized by the U.S. Weather Bureau—now the National Weather Service (NWS)—as a record-setting event.

At approximately 7:30 a.m., the temperature soared from –4°F to 45°F in only two minutes as warm, dry Chinook winds cascaded down the eastern slopes of the Rocky Mountains. According to historical records maintained by the National Oceanic and Atmospheric Administration (NOAA), Chinook winds can raise temperatures rapidly, but the surge in Spearfish was exceptional even by regional standards. The extreme heat burst was so sudden that frost evaporated instantly, car windshields defrosted in seconds, and several store and house windows cracked from the rapid expansion of glass.

The atmosphere continued to warm after the initial jump, eventually reaching 54°F later that morning—an astonishing contrast to the deep freeze just hours earlier. However, the dramatic warm spell did not last. Shortly before 9:00 a.m., the Chinook winds abruptly died, and cold Arctic air rushed back over the town. In a stunning reversal, the temperature plunged from 54°F back to –4°F in only 27 minutes. Local newspapers from the period, including reports later archived by the South Dakota State Historical Society, described the event as “weather in fast-forward,” as residents stepped from springlike warmth straight back into midwinter.

In less than an hour, Spearfish had cycled through a temperature range of nearly 60 degrees—a shift so violent and rare that meteorologists still cite it as one of the greatest examples of atmospheric turbulence ever observed in the United States. The 1943 Spearfish temperature swing remains a frequently referenced case study in discussions of rapid weather variability, showcasing the extraordinary power of Chinook winds and the unpredictable dynamics of mountain meteorology.