Do Tornadoes Always Come From the Southwest?

By Chris Martz | May 29, 2019

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"Do tornadoes always come from the southwest?" - Nancy Martz

WeatherFact:

Dear, Nancy,

This is an interesting question and believe it or not, it's one of the most frequently asked questions that meteorologists receive! This is one of only a handful of weather folklore beliefs that is actually backed up by science.

The majority of tornadoes do indeed generally travel in a southwest to northeast direction, however, they may spawn and move in any direction along a horizontal plane. Most tornadoes originate from supercell thunderstorms, which like most storm systems, move in a west to east or southwest to northeast direction in the Northern Hemisphere.

So, then this begs the question why storms move west to east?

The reason for this is because the troposphere's maximum height varies from the poles toward the equator. Near the poles, the troposphere is approximately 4 miles high, whereas it's almost 12 miles high near the equator. This is because warmer things expand and cooler things contract. 

This variation in the troposphere's altitude sets up a downward slope from the equator, poleward. As a pocket of air known as a 'parcel' slides down the slope, it moves from south to north and with the Earth's counterclockwise spin on it's axis, the Coriolis force pushes that parcel eastward thereby creating the southwest to northeast flow.

REFERENCES

[1] Edwards, Roger. "The Basics About Tornadoes." The Online Tornado FAQ. Accessed May 29, 2019. https://www.spc.noaa.gov/faq/tornado/.

[2] Jimenez, Jesus. "Why Do Tornadoes Always Seem to Travel Southwest to Northeast? Curious Texas Investigates." Dallas News. January 14, 2019. Accessed May 29, 2019. https://www.dallasnews.com/life/curious-texas/2019/01/14/tornadoes-always-seem-travel-southwest-northeast-curious-texas-investigates.