Tornadoes
A thunderstorm's spinning arm reaches the ground, gets graded by the damage it leaves, and is forecast better than ever but never perfectly.
By Greg Goodwin · Published November 4, 2026
Cheat Sheet
- EF scale: EF0 is 65 to 85 mph and EF5 is over 200 mph, as estimated 3-second gusts (EF1 86-110, EF2 111-135, EF3 136-165, EF4 166-200).
- Rating system: the Enhanced Fujita Scale became operational on February 1, 2007, using 28 damage indicators and 8 degrees of damage.
- Frequency: roughly 1,200 tornadoes a year in the US; NOAA's preliminary 2025 count was 1,559, fifth-highest on record.
- Deadliest: the Tri-State Tornado of March 18, 1925 killed 695 people; its official path length is 219 miles.
- Latest EF5: Enderlin, North Dakota on June 20, 2025, the first EF5 in 12 years after Moore, Oklahoma on May 20, 2013.
- Reach: tornadoes occur at any hour and any time of year and have been reported in all 50 states (NWS).
The 60-Second Version
A tornado is a violently rotating column of air that extends from the base of a thunderstorm down to the ground. The strongest ones typically come from rotating thunderstorms called supercells, though exactly how and why the spin reaches the surface is still a subject of active research. Forecasters watch for the conditions that favor them, then use radar to spot rotation inside storms and issue warnings. Tornadoes are most common in the Central Plains and the southeastern United States, but they have been reported in all 50 states and can strike at any hour. Their strength is rated after the fact by surveying damage, so the official number tells you what the storm did, not what a wind gauge measured. The ratings run from EF0 to EF5, and the top of the scale is rare. Knowing the difference between a watch and a warning, and where to shelter, is the practical skill that matters.
The Long Version
What a Tornado Actually Is
The National Weather Service defines a tornado as a violently rotating column of air extending from the base of a thunderstorm down to the ground. Tornadoes can completely destroy well-made structures, uproot trees, and hurl objects through the air as missiles. A visible funnel is not the whole story, since the damage is caused by wind at the surface, and a tornado is defined by contact with the ground. They can occur at any time of day or night and at any time of the year. Although most common in the Central Plains and southeastern United States, they have been reported in all 50 states.
How They Form, and What Is Still Unsettled
The storms most associated with strong tornadoes are supercells, thunderstorms with a rotating updraft. Radar can detect rotation, and a mesocyclone signature has historically come before many tornadoes. But the step from a rotating storm to a tornado on the ground is not fully understood. One study of 16 southern US tornadoes found that only half of the mesocyclone-related cases developed from a descending mesocyclone core. The short version is that forecasters are good at recognizing the setup and the radar signature, and still working out which rotating storms will actually produce a tornado.
Measuring Strength: The Enhanced Fujita Scale
The Enhanced Fujita Scale, or EF Scale, became operational on February 1, 2007, replacing the original 1971 Fujita scale. After a tornado, trained NWS surveyors compare damage to 28 damage indicators and 8 degrees of damage to estimate the highest wind within the damage path. The ratings run from EF0, 65 to 85 mph, up to EF5, over 200 mph, using three-second gust estimates. The NWS stresses that these are estimates, not measurements, and that the NWS is the only federal agency that can issue official ratings. Because the scale is based on damage, a powerful tornado that crosses open country with little to damage can end up with a lower rating than its winds deserved.
How Often, and Where
The Congressional Research Service puts the US average at roughly 1,200 tornadoes a year. NOAA's preliminary count for 2025 was 1,559, which its national climate summary ranked fifth-highest on record and 127% of the 1991 to 2020 average; AccuWeather, using preliminary Storm Prediction Center data, reported 1,558. Preliminary counts get revised, and long-run averages depend on the period and counting method, so estimates vary. Tornado Alley, the central US region of relatively frequent tornadoes, is a media-coined term rather than an official boundary, and the southeastern states are also a high-frequency region.
Worst Cases and Warnings
The Tri-State Tornado of March 18, 1925 killed 695 people, the deadliest on record in the US, with an official path of 219 miles. One reexamination put the path nearer 234 miles, and other reanalysis argues it may have been a family of tornadoes rather than a single one. The most recent EF5 tornadoes were the Moore, Oklahoma tornado of May 20, 2013, which killed 24, and the Enderlin, North Dakota tornado of June 20, 2025. Warnings have improved: lead time averaged about five minutes in 1986, when only 25% of tornadoes were warned, and a mean of 13 minutes by 2004.
Why People Care
Tornadoes can arrive with minutes of warning, so a plan made in advance is worth more than any forecast. Understanding watches, warnings, and ratings turns scary news into information you can act on.
Glossary
- Supercell
- A thunderstorm with a persistent rotating updraft, the storm type behind many of the strongest tornadoes.
- Mesocyclone
- The rotating column of air inside a supercell that radar can detect, often before a tornado forms.
- Enhanced Fujita Scale
- The rating from EF0 to EF5 assigned from surveyed damage, which estimates the tornado's peak wind.
- Tornado Alley
- A media-coined name for the broad area of the central US where tornadoes are relatively frequent.
- Tornado warning
- An alert that a tornado has been sighted or indicated by radar, as opposed to a watch, which means conditions are favorable.
Go Deeper
More to Explore
- Hurricanes
A hurricane is a giant heat engine powered by warm ocean water, and when it runs out of fuel it falls apart.
- Volcanoes
About 75% of the world's active volcanoes crowd into one Pacific horseshoe, aptly nicknamed the Ring of Fire.
- Earthquakes
Most earthquakes are too small for any human to feel, caught only by seismometers quietly logging the ground's tiny movements.
- Renewable Energy
Within about a decade, solar and wind went from pricey idealistic alternatives to cheaper than fossil fuels in many regions.
- Plate Tectonics
A theory that explains why South America and Africa's coastlines look like they'd fit together — because, hundreds of millions of years ago, they did.