On the Terra MODIS true color image (above) an extensive cumulus field can be seen forming over the land surfaces surrounding Lake Michigan on 15 September — daytime heating along with the evaporation of abundant soil moisture (from significant precipitation on 12 September and 13 September) allowed the cumulus clouds to form quickly as the day progressed (Aqua MODIS image 3 hours later). In lower Michigan, a differential heating boundary is quite evident, where the dissipation of thick morning fog and stratus was delaying the cumulus formation; a well-defined lake breeze boundary also developed along the Lake Michigan lakeshore counties, which was quite apparent in Wisconsin and Illinois on the later Aqua MODIS image.

Two other items of interest on the MODIS true color image above: (1) the first regional sign of peak Autumn tree color is showing up in southern Ontario; note the amber color along the eastern shore of Lake Superior (closer view), and (2) farther east, the light gray features over Quebec are areas of smoke aloft, from wildfires in Ontario 1-2 days earlier.