You frequently state that Chicago area temperatures are 10-15 degrees cooler at the lakefront compared to readings further inland. Is there a period of time during the year when Lake Michigan is sufficiently warmer, causing the reverse: temperatures warmer at the lakefront than inland?
Yes, especially during the winter. Air over Lake Michigan loses heat to the water when its temperature is above the lake’s surface temperature, but it gains heat when it is colder. Lake water temperatures, always 32 degrees or higher, thus act as a mechanism either to chill or to warm air over the lake.
When cold air whose temperature is well below the surface lake water temperature moves over the lake, it warms. Then, if that warmed air moves back over land, it will have a higher temperature than air farther inland that has not been warmed. This is often the situation in the winter.