Alex's post on Friday shows a widespread area of moderate AQI throughout the Great Lakes region. The situation has not cleared significantly as of Sunday morning. CALIPSO's overpass of the region yesterday (map and cross section) shows that there is a widespread area of haze thoughout the midwest and into the Great Lakes. The layer of haze is low. Below left, the radiosounding from Green Bay, WI, shows a deep (1600m) stable layer of air this morning at 0600 CST. Pollutants emitted into this strongly capped inversion tend to stay concentrated at the surface. Thus, we have a number of cities in Wisconsin, Illinois and Michigan that are elevated to at lease the "moderate" level and a few at the "unhealthy for sensitive groups" reading of orange.
The concentration of PM2.5 in Milwauwee is over 40 µg m-3.