Tornado counts are considered preliminary until final publication in the database of the National Centers for Environmental Information.
[1] On average, there are 66 confirmed tornadoes in the United States in September, 59 in October, 54 in November and 28 in December.
A secondary focal point lies in the Midwest and Great Lakes as a result of early-autumn frontal systems.
[3] While tropical activity tends to decrease in October, the relative peak shifts into the Great Plains and towards the southern states as the jet stream shifts southward (albeit generally with less activity than in the spring months in the same regions).
[4] In November and December, these tornadoes are most likely in the southern states due to their proximity to the unstable airmass and warm waters of the Gulf of Mexico, with occasional incursions farther north into the Midwest especially in November.