Clouds quickly developed over southern Wisconsin Saturday morning as temperatures increased. However, where cool, dense air pushed in from Lake Michigan on southeast winds, clouds quickly vanished. The location of the lake breeze in the visible satellite loop below would be along the sharp gradient between clear and cloudy skies.
Lake breeze development is typical in the spring time, when lake surface temperatures are their coolest and land surface temperatures can rise to much higher values. When winds are light enough, the cool, dense air over Lake Michigan is able to push onshore, undercutting the warm, less dense air already over the land.