Dear Tom,

We were wondering why it’s normally incredibly windy when we experience above-average temps during the colder months.
Keegan Bouma and Christina Digioia, Grayslake

Dear Keegan and Christina,

Your observation is right on. By definition, unseasonably warm weather occurs during the colder times of the year when warm weather is confined to the southern states. Strong atmospheric forces are needed to transport the warm air as far north as Chicago, and the best mechanism for doing this is an intense low-pressure area passing north of the city. Strong southerly winds ahead of the storm enable the warm air to surge northward. Once the storm system moves east of Chicago, winds shift to the northwest, and a sharp turn to colder weather follows. If warm air were to move into Chicago in winter or spring with light winds, onshore flow off of chilly Lake Michigan, would quickly develop, putting a lid on rising temperatures in the city.