When the Atlantic coast prepares for a hurricane, Chicago has beautiful weather?

Dear Tom,
It sure seems like when the Atlantic coast prepares for a hurricane, Chicago has beautiful weather. Is there any truth to this?
— Richard Laschober, Vernon Hills
Dear Richard,
There is a ton of truth to your statement. When an Atlantic or Gulf hurricane approaches the U.S. mainland, it tends to set up a blocking or slowing effect on eastward-moving weather systems moving across the Midwest, holding rain-producing cold fronts at bay. Additionally, hurricanes have vast circulation fields. Air venting out of the top of a hurricane eventually subsides hundreds and even thousands of miles away from the storm. That subsiding air warms and dries, bringing a string of sunny and warm days, similar to the weather currently gracing Chicago. September 1979, Chicago’s all-time driest month with just 0.01 inch of rain, was a month that featured four hurricanes approaching the U.S.

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