The warmth preceding the blizzard of January 1967

Dear Tom,
Two days before Chicago’s 23-inch blizzard of January 1967, conditions were unseasonably warm. Did that have anything to do with the amount of snow that fell?
David Wechsler, Glenview
Dear David,
The warmth that preceded the blizzard sent Chicago-area temperatures surging to a 65-degree record high on Jan. 24 and undoubtedly added to the severity of the storm. The warm air, flooding into the Midwest, fed large amounts of moisture into the storm system, fueling severe thunderstorms and heavy rainfall. When the cold air arrived, the sharply contrasting temperatures resulted in rapid cyclogenesis (storm formation), and with large amounts of moisture already in the air, heavy snow began to fall. The storm’s first wave of snow produced about a foot, but then an unexpected second low-pressure system formed, nearly doubling the storm’s snow totals.

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