Explainer, PAUL MERZLOCK

Winds gusting over 50 mph Saturday night swept sharply colder air across the Midwest. The current cold snap is in contrast to what has been one of the mildest winters on record. Temperatures are forecast to bottom out Tuesday morning when pre-dawn readings dip as low as 5 below zero in portions of the Chicago area. The cold is then expected to gradually ease, though readings will stay below normal into the upcoming weekend. High temps are forecast to remain below freezing through Saturday. If this verifies, this will be the longest stretch of sub-freezing weather since late January and early February of 2011, in the days surrounding the blizzard of 2011. The longest period of sub-freezing temps occurred during the brutal winter of 1976-77 when the mercury failed to reach freezing for 43 consecutive days.