In October, as the length of sunlight begins to fade across the upper reaches of the Northern Hemisphere, cold air begins to build across the arctic. Snow is not uncommon and the depth and coverage of the snowpack is an important element in helping to build a reservoir of cold air across the region. The cold air strengths and is triggered southward by large wave patterns in the high atmosphere. In the later days of October 1919 heavy snows fell across the Yukon and other areas of northern Canada. Cold air built quickly and was released southward in the last week of the month. And so, it came to pass that on October 26, 1919 that arctic blast reached Bismarck, North Dakota and the mercury plunged to 10 below zero, the coldest temperature ever recorded in Bismarck in the month of October and the earliest, up to that time that the temperature dropped below zero.
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