Analysis of winds aloft show that a large amplitude wave in the jet stream has become established over central and eastern North America sending air from the Canadian Arctic directly into the Midwest. This has kept our temps running nearly 10 degrees below normal over the weekend. Conditions are going to worsen before they get better. Satellite imagery late Saturday identified a core of fast-moving air within the jet stream over northern Canada. As this feature drops southward Sunday and Monday it will act to deepen a pool of unseasonably cold air over the western Great Lakes. This set-up may produce spotty snow showers as far south as northern Illinois on Monday. Snow showers, mixed at times with rain, are likely over portions of NW Indiana and SW Michigan. High temps Monday afternoon are forecast to run about 20 degrees below normal. The late November-level chill will be compounded by NW winds gusting over 40 mph. Though these conditions are to improve by midweek, sub-normal temps will linger through Thursday before a significant warm-up arrives.

Winds to howl as temperatures change

Chicago to truly be a “windy city”in coming days. Rapid temperature changes are usually associated with elevated wind speeds. Zones of rapid temperature flux produce changes in air pressure, which in turn increase wind speed. This is why average wind speeds are greater in transition seasons than during summer, when the hemisphere is more uniformly warm.