Early November was notable by virtue of abnormal warmth, with the first 11 days of the month producing daily temperature surpluses. Despite daytime readings in the 30s this past weekend, the month was still posting a whopping plus 8-degree departure from normal heading into Monday. That temperature surplus will be largely eradicated over the next 10 days as a wintry pattern evolves. Satellite imagery late Monday showed a vigorous disturbance over the Red River valley of the southern plains. This system will lift NE across Indiana Tuesday morning, spreading a swath of accumulating snow into the Chicago metro area. This first measurable snow of the season will be ill-timed, coinciding with the morning commute. Occasional snow may linger into midweek as a weaker, secondary system makes its way across the western Great Lakes. It is behind this feature that very cold air (by mid-November standards) arrives. By Friday upper-level wind flow over Chicago will arrive directly from the Canadian arctic. Highs Thursday may struggle to reach freezing. Max temps Friday and Saturday are expected to hold in the 20s, making them our first occurrence of sub-freezing days this season.