00:48 Sioux Falls Tornado Rips Apart Building in Newly Released Footage Newly released footage from inside a health center in Sioux Falls shows the damage done by an EF-2 tornado that struck the city one year ago.

At a Glance Tornadoes are most likely to occur in the South in January.

This is due to its closer proximity to more humid air in the Gulf of Mexico.

There have been large tornado outbreaks in January, most recently in 2017. January's reputation for bone-chilling cold usually doesn't make you think of tornadoes ripping up homes and trees, but they happen most years, and sometimes there can be large outbreaks.

The South is the region most likely to experience tornadoes in January, and occasionally tornadoes can spin up farther north. This so-called Dixie Alley is most likely area to get tornadoes in other colder months from fall into early spring.

<img class="styles__noscript__2rw2y" src="https://s.w-x.co/util/image/w/jan_tor_climo_0.jpg?v=at&w=485&h=273" srcset="https://s.w-x.co/util/image/w/jan_tor_climo_0.jpg?v=at&w=485&h=273 400w, https://s.w-x.co/util/image/w/jan_tor_climo_0.jpg?v=ap&w=980&h=551 800w" > Lighter red is where there is a 0.10 percent or greater probability of a tornado within 25 miles of a point by mid-January. Darker red is where there is a 0.20 percent or greater probability of a tornado within 25 miles of a point by mid-January. Based on 1982-2011 averages. (NOAA/Storm Prediction Center)

A near perfect marriage between moisture and potent atmospheric triggers, like a low-pressure system and strong jet stream, must exist for tornado-producing thunderstorms to form in winter.

Because the South is closest to the milder and more humid air of the Gulf of Mexico, it's the most-favored location for these ingredients to overlap in January. The biggest question when forecasting severe weather this time of year: Will sufficiently humid air move far enough north to destabilize the atmosphere and allow thunderstorm to form?

<img class="styles__noscript__2rw2y" src="https://s.w-x.co/util/image/w/severe-setup-example.jpg?v=at&w=485&h=273" srcset="https://s.w-x.co/util/image/w/severe-setup-example.jpg?v=at&w=485&h=273 400w, https://s.w-x.co/util/image/w/severe-setup-example.jpg?v=ap&w=980&h=551 800w" >

Over the last 20 years, an average of 42 tornadoes have occurred in the U.S. in January. That's the third fewest of any month, but is roughly the same as December and February.

A January record 212 tornadoes hit the U.S. in 1999. There have also been years without a single January tornado, most recently in 2003.

<img class="styles__noscript__2rw2y" src="https://s.w-x.co/util/image/w/avg-tornadoes-by-month.jpg?v=at&w=485&h=273" srcset="https://s.w-x.co/util/image/w/avg-tornadoes-by-month.jpg?v=at&w=485&h=273 400w, https://s.w-x.co/util/image/w/avg-tornadoes-by-month.jpg?v=ap&w=980&h=551 800w" > The 20-year average number of tornadoes in the U.S. per month from 1999 to 2018.

January 2017 is the most recent active January with 137 tornadoes.

The largest outbreak that month was Jan. 20-22, when 79 tornadoes were spawned in the South . Twenty people were killed in Georgia and Mississippi.

A record-breaking January outbreak occurred in 1999 when 129 tornadoes struck in two days, mostly in the South.

The deadliest January tornadoes on record both killed 55 people. One of them was Jan. 3, 1949, in Warren, Arkansas, and the other was Jan. 11, 1898, in Fort Smith, Arkansas.

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