The trend of Chicago’s temperatures, already a few degrees below normal and certainly on the cool side, will be downward through the current seven-day forecast cycle as strong, persistent northwesterly winds 15,000 to 30,000 feet aloft direct surges of chilly Canadian air across the Midwest and Great Lakes region.
Outbreaks of Canadian air at this time of year typically bring air temperatures considerably lower than ground temperatures, and that implies atmospheric instability sufficient to generate plenty of cloudiness and, given sufficient instability, even showers. That’s expected to be the situation here as air temperatures become cooler and cooler in coming days. Scattered instability showers will be likely by Monday.
Air aloft eventually becomes cool enough – Tuesday through Thursday – to trigger lake-effect rain showers downwind of Lake Michigan. Northwesterly winds mean lake-effect showers will be confined to the Indiana and Michigan shores of the lake.
It’s even possible that temperatures aloft will become cold enough to support the development of snow showers.
Story by Richard Koeneman, Chicago Weather Center blogger
For more information, go to ChicagoWeatherCenter.com.