On January 22nd, 1943, Spearfish achieved a world record for the largest variance in temperature in the shortest amount of time. Chinook winds were behind the temperature rise, measured at minus 4 degrees at 7:30 in the morning, increasing 49 degrees in just two minutes. At 7:32 am, the official temperature was 45 degrees above zero.
Chinook winds in the western interior of the United States are generally called föhn winds by meteorologists but are still more commonly known as "Chinooks". Regardless of the name, they form on the leeward side of a mountain range. Moist air masses moving west to east are driven up the western side of mountains, cool down, and drop their moisture, as the now dry air goes down the eastern side of mountains, it heats up as it loses elevation and increases in speed. Occasionally the the speed of the wind and the temperature change it causes can be extraordinary.
Chinook winds helped Loma, Montana achieve the world record for the most extreme temperature change in a 24-hour period. On January 15, 1972, the temperature increased from −54 °F to 49 °F above zero, a temperature difference of 103 °F.
However, Spearfish still holds the world record for the fastest increase in temperature, warming 49 °F in just 2 minutes.
But it can happen in reverse. As that day went along, the overall temperature in Spearfish had increased to 58 degrees. When the Chinook died down, the temperatures began to fall again. It took just 27 minutes for the temperature to plunge from back to -4 degrees. The shift was so quick that windows frosted over, and many cracked from the sudden temperature change.
The record temperature extremes occurred in Spearfish on January 22nd, 1943.
Production help is provided by Doctor Brad Tennant, Professor of History at Dakota Wesleyan University.