Chicagoans waited until afternoon Sunday, then sleet mixed with light snow began to fall - changing over to freezing rain by late afternoon into the evening hours. Up to a quarter-inch of glaze formed on limbs, sidewalks, vehicles and solid exposed surfaces. Traffic slowed on the main highways with scattered accidents - while conditions for travel and outdoor activities were treacherous elsewhere. There were numerous thunder and lightning reports - the violent up/downdrafts in the storms creating brief heavy snow and sleet at isolated locations. By 9pm most observing points around the area were reporting temperature at or above freezing and slowly rising. With temperatures expected to warm up to around 40 degrees by Monday forenoon, a good portion of the glaze was expected to melt overnight.
Record warmth/storms Tuesday
We should experience quite a variety of weather in the week ahead! Southerly winds are expected to gradually strengthen with warm air pouring into the Midwest and Great Lakes ahead of a cold front forecast to move southeast - passing through Chicago later Tuesday. Temperatures aloft will warm first, creating a sharp temperature inversion, where temperatures increase rapidly with height - trapping clouds and haze over the metro area Monday. By Monday night conditions will become more unstable with strengthening winds and increased low-level moisture leading to the development of showers and possible thunderstorms. For the second straight night temperatures will slowly rise Monday night, so that 50-degree temperatures could greet residents to the start the day Tuesday. Showers and thunderstorm downpours with even the possibility of severe storms could occur during the day Tuesday - as temperatures threaten the 59-degree record high set 99 years ago in 1914. One to two-inch rainfall on top of frozen ground could result in significant runoff, and the warm temperatures could melt ice on the rivers creating ice jams - all resulting in high flood potential.
Arctic cold follows
Temperatures will fall sharply Tuesday night after the cold frontal passage as strong northwest winds usher in the leading edge of a southward-moving Arctic high pressure air mass. Chicago will finds itself deeper and deeper into the cold air as the Arctic high pressure settles farther south the latter half of the workweek. Highs in the teens and sub-zero wind chills can be expected here next Thursday and Friday.