Forty of the most common tornado questions, answered in plain English with links to deeper reading.
A tornado is a violently rotating column of air extending from a thunderstorm cloud to the ground. It's the most concentrated form of atmospheric wind on Earth.
Most tornadoes form from a specific storm type called a supercell. Wind shear tilts the storm's updraft; a horizontal rolling motion near the surface gets tilted vertically by the updraft, creating a rotating column called a mesocyclone. When the mesocyclone tightens and reaches the ground, it's a tornado. See step-by-step formation.
The highest wind speed ever measured on Earth was 301 mph, in the 1999 Bridge Creek-Moore, OK F5.
Average duration is about 10 minutes. The longest continuous tornado, the 1925 Tri-State, stayed on the ground for approximately 3.5 hours.
The average tornado is 50-200 yards wide. The record widest was 2.6 miles (El Reno, OK, 2013).
The Enhanced Fujita Scale rates tornado intensity from EF0 to EF5 based on damage. EF0 winds are 65-85 mph; EF5 winds are 200+ mph. See interactive EF scale explorer.
Tornadoes happen on every continent except Antarctica, but about 75% happen in the United States. Traditional Tornado Alley covers Texas, Oklahoma, Kansas, Nebraska. Dixie Alley covers Mississippi, Alabama, Tennessee, Arkansas. See tornado alley map.
US peak season is April, May and June. Southeast tornadoes are common in December-February. Tornadoes can happen any month. See month by month.
Yes. Nighttime tornadoes are 2.5 times more likely to be fatal than daytime ones because people are asleep. Dixie Alley has a high proportion of nocturnal outbreaks.
Texas has the most per year (about 135). Oklahoma has the most per square mile.
Yes. Downtown Dallas, St. Louis, Nashville, Atlanta and Salt Lake City have all been hit. The "cities repel tornadoes" idea is a myth.
The 1999 Bridge Creek-Moore, OK F5 measured 301 mph. That's the highest measured wind speed on Earth.
The 1989 Daulatpur-Saturia tornado in Bangladesh killed approximately 1,300 people. The deadliest US tornado was the 1925 Tri-State (695 dead).
The 1925 Tri-State Tornado tracked 219 miles across Missouri, Illinois and Indiana.
No. The EF Scale caps at EF5. No matter how strong a tornado is, EF5 is the highest possible rating.
The 2013 El Reno, Oklahoma tornado at 2.6 miles wide. Rated EF3, but held the width record.
Best: underground shelter or basement. Second best: interior room on lowest floor without windows. See safety by location.
No. This is a myth. Windows don't equalize pressure meaningfully, and opening them wastes shelter time. See 15 myths debunked.
No. Overpasses funnel wind and offer no debris protection. Lie flat in a low ditch away from vehicles and trees if you're outside with no building nearby.
Watch = conditions favorable; Warning = tornado sighted or radar-indicated. See watch vs warning.
Average is 13 minutes. Some give zero warning; some give 30+.
Water, food, first aid, NOAA radio, flashlight, cash, documents, medications, whistle. Use our kit builder.
Wind shear creates horizontal rotation which the storm's updraft tilts vertical. The rotating column is stretched by the rising air, which speeds up the spin (conservation of angular momentum).
Northern Hemisphere: counterclockwise (cyclonic) in almost all cases. Southern Hemisphere: clockwise. Rare anticyclonic tornadoes rotate the opposite way in either hemisphere.
Low-pressure rotating air, condensation forming the visible funnel, and swirling debris. Peak wind speeds are near the ground; pressure drops of 100 mb have been measured inside.
Yes. Satellite tornadoes are small tornadoes orbiting a larger primary tornado. Multi-vortex tornadoes have sub-vortices within the main circulation.
A rotating updraft within a supercell — the parent circulation that spawns most significant tornadoes. See what is a mesocyclone.
Yes, on public roads and public land. Trespassing rules still apply.
They read SPC outlooks and mesoanalysis in the morning, drive to a target region, watch radar and visual cues, position south/southeast of promising supercells. See our beginner guide.
A hook-shaped extension of a supercell's reflectivity on radar, curved around the mesocyclone. One of the strongest single indicators of tornado potential. See hook echo explainer.
You can see radar reflectivity, velocity and warnings on apps like RadarScope. You'll see hook echoes and debris signatures but not the tornado itself unless you're looking at real-time video.
No. When one appears to "lift and drop," it's usually two separate tornadoes from the same parent mesocyclone. See myths debunked.
No. Tornadoes don't reliably come from the southwest, and debris ricochets. Get under sturdy furniture in an interior area.
No. Tornadoes routinely cross the Mississippi, Missouri, Ohio and many other rivers.
Yes — this description is consistent across decades of survivor testimony. See the actual physics.
The overall count isn't rising, but tornadoes are increasingly clustered into big outbreak days and shifting eastward into deadlier Dixie Alley. See climate change and tornadoes.
About 1,200 on average, with year-to-year variation from ~900 to ~1,800.
Direct damages average $1-3 billion per year. Peak years like 2011 cost $10+ billion. See costliest tornadoes.