Explainer, PAUL MERZLOCK

Snow was not observed at O'Hare International Airport on Sunday. This means that the city has officially set a record for the latest occurring measurable snowfall. Winter has come early elsewhere. The upper Midwest has recently received heavy snow. Central and eastern Europe has shivered in sub-zero temperatures. November 29th, Moscow, Russia was blanketed by its heaviest snowfall in 50 years. Hemispheric weather patterns are changing. Winter weather in Europe appears to be easing. Meanwhile, computer guidance continues to suggest Chicago's mild December may be about to turn wintry. Intensifying low pressure is currently forecast to pass across the area on Thursday. Cold air available to this system is expected to change rain to snow. Accumulations appear likely at this time.