Cooling in Chicago: back-door cold front, sea breeze or lake breeze?


Dear Tom,

I have heard the terms “back-door cold front”, “sea breeze” and “lake breeze” used to describe cooling here in Chicago. What are the differences?

Marilyn Richter,
Downers Grove

Dear Marilyn,

Sea and lake breezes refer to the same phenomena. Sea/lake breezes form when the sun heats land adjacent to a cooler body of water. Heated and less dense “land air” rises and is replaced by cooler air originating over the water. Meteorologically, the effect is a small scale one.

A back door cold front is a synoptic, large scale event caused when the upper air pattern becomes so longitudinal (large north/south flow patterns) that cold fronts can move in from the northeast. The effect is enhanced over Lake Michigan due to cooler water. “Back door” refers to the unusual northeast direction of the frontal origin. Most cold fronts come through the “front door”—from the northwest.


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