Hurricane Frances, September 2004: 103 tornadoes. Tornado expert Dr. Greg Forbes says Frances spawned the second highest number of tornadoes for a U.S. landfalling tropical cyclone.
Spring is known for its strong storm systems that can create violent twisters. However, it's not the only season known for tornadoes. Autumn is considered the "second" tornado season.
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"The second half of October and especially November can often be a second season for tornadoes and severe thunderstorms," said tornado expert Dr. Greg Forbes. "In many ways, this is the counterpart to spring, when strong fronts and upper-air systems march across the United States. When enough warm, moist air accompanies these weather systems, the unstable conditions yield severe thunderstorms and sometimes tornadoes."
While most of the largest tornado outbreaks still occur in spring, autumn has its share of storms as well. Dr. Forbes examined the storm statistics and found six of the largest 55 known tornado outbreaks occurred in October and November.
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May is still the peak month for tornadoes. Up to 52 percent of September's tornado outbreaks are due to landfalling tropical storms and hurricanes. October and November's tornadoes are caused by strong cold fronts and low pressure systems affecting the South and sometimes the Midwest.
So far, 2013 is on pace to be a record low tornado year. January was the only month that's been above average for tornadoes. It had 74 tornadoes, 2.3 times the average number of tornadoes.
The numbers don't mean it has been an easy tornado year. At least 46 people have died in the U.S.from tornadoes this year. Two extremely destructive tornadoes devastated towns in Oklahoma in May. A severe storm system Oct. 2 may have spawned as many as 12 tornadoes, according to preliminary estimates.
"It's a been a year with some notorious tornadoes," said Forbes said.
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