Dear Tom,
Is there ever a time of the year when there is a zero chance of a tornado touching down in the United States?
— Margaret Robertson, Chicago
Dear Margaret,
There is not. The chance of a tornado occurring in the spring or summer is greatly better than the chance in the fall and even more so than in the winter, but tornadoes have been reported in the United States in every part of the year. About half of all tornadoes form in the late afternoon, between 3 and 7 p.m., with 5 p.m. being the hour of greatest occurrence, but they have occurred at all hours of the 24-hour day. May is the month of greatest tornado occurrence in the United States, followed by June, April and July. In the winter, tornadoes develop most frequently in the Gulf states, then maximum occurrence shifts to the southern Plains in the spring, then gradually shifts north to the northern Plains in August.
Is there ever a time of the year when there is a zero chance of a tornado touching down in the United States?

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Is it possible for a tornado to form during the winter?
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What state has the worst weather in the United States?
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Over 20 tornadoes reported in central Illinois during rare blitz of twisters
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Did the past winter produce thunderstorms in December, January and February?
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When was the last time Chicago’s daily high temperature didn’t go above zero?
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This fall we’ve had three official one inch or more snowfalls before Thanksgiving. Has this ever happened before in Chicago?
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What is the record for the greatest amount of snow ever to occur in one hour in Chicago?
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Why shouldn’t we open windows when a tornado threatens?
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Did Chicago not experience an Indian summer this year?
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Has Chicago ever recorded the nation’s highest or lowest temperature?
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What was the greatest 24-hour increase in Chicago temperatures?
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Canceled flights, delayed trains and icy roads as winter storm moves east
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Who defines how much snow a storm must produce to be a blizzard?