After an unseasonably warm start to January, with temperatures soaring into the 40s and 50s across major Midwest cities like Chicago and Detroit, a dramatic shift is on the horizon. Arctic air is poised to sweep southward this week, ushering in a period of significantly colder temperatures and the threat of snow. By the latter part of the week, daytime highs are expected to plummet into the teens and 20s, representing a staggering temperature swing of up to 40 degrees in some areas. Residents should prepare for a sharp transition to more typical winter conditions.