Wintry weather

People brace themselves as wind and snow blow Monday in Chicago. (AP Photo/Charles Rex Arbogast)

Q: What causes cold air outbreaks?

A: A vigorous cold air outbreak is usually a midwinter, not late fall, phenomenon.

As with most unusual events in the atmosphere, a cold air outbreak is a commingling of circumstances — some common and some not — brought to extreme by perfect timing.

"Weather Guys" Steve Ackerman and Jonathan Martin are professors in the University of Wisconsin-Madison department of atmospheric and oceanic sciences.

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