Tornado
A tornado is a violently rotating column of air in contact with the ground, extending from a thunderstorm. Tornadoes are rated from EF0 to EF5 on the Enhanced Fujita scale by the damage they cause. Most last less than 10 minutes, but the strongest can stay on the ground for more than an hour.
Why It Matters
A tornado has to be touching both the ground and a convective cloud at the same time; a rotating funnel that has not reached the ground is a funnel cloud. Tornado winds are rarely measured directly, so intensity is estimated afterward from the damage.
The most destructive and deadly tornadoes come from supercells, the rotating thunderstorms that also produce the largest hail. Many supercells never produce a tornado at all, which is why forecasters talk about tornado potential in probabilities.
Enhanced Fujita Scale Ratings
| Rating | Estimated 3-second gust |
|---|---|
| EF0 | 65 to 85 mph |
| EF1 | 86 to 110 mph |
| EF2 | 111 to 135 mph |
| EF3 | 136 to 165 mph |
| EF4 | 166 to 200 mph |
| EF5 | Over 200 mph |
Wind speeds are estimates worked out from damage after the tornado, not measurements.
Key Facts
- Tornadoes last from several seconds to more than an hour. Most last less than 10 minutes.
- The average tornado path since 1950 is about 3.5 miles long.
- A tornado does not always have a visible funnel. Dust or debris swirling at the ground can be the only sign.
- On radar, a tornadic storm may show a hook echo, tight rotation in velocity data, and a debris ball once debris is lofted.
Frequently Asked Questions
What is the difference between a tornado watch and a tornado warning?
A tornado watch covers a group of counties where tornadoes are possible over the next several hours: stay alert and be ready to shelter. A tornado warning means a tornado has been spotted or radar shows a storm circulation that can produce one: take shelter immediately.
What is the difference between a funnel cloud and a tornado?
Contact with the ground. A funnel cloud is a rotating column hanging from the cloud base that has not reached the surface. Once the rotating column of air is in contact with the ground, it is a tornado, whether or not the visible funnel extends all the way down.
How are tornadoes rated?
On the Enhanced Fujita scale, from EF0 to EF5. Survey teams examine the damage after the storm and estimate the 3-second wind gust that caused it. EF0 corresponds to 65 to 85 mph and EF5 to over 200 mph.
Related Terms
Enhanced Fujita Scale
The Enhanced Fujita (EF) scale rates tornadoes from EF0 to EF5 based on the damage they cause. Surveyors compare the damage to 28 kinds of buildings, structures, and trees against expected levels of damage, then estimate the 3-second wind gust responsible. EF0 means estimated gusts of 65 to 85 mph, and EF5 means over 200 mph.
Supercell
A supercell is a thunderstorm with a deep, persistently rotating updraft called a mesocyclone. Supercells are the most dangerous type of thunderstorm: they produce nearly all significant tornadoes in the United States and most hail larger than golf balls, along with damaging winds and flash flooding.
Mesocyclone
A rotating vortex of air within a supercell thunderstorm, typically 2-6 miles in diameter. Mesocyclones are detected by Doppler radar and indicate the potential for tornado development.
Funnel Cloud
A rotating cone-shaped cloud extending downward from the base of a thunderstorm but not reaching the ground. When a funnel cloud touches the ground, it becomes a tornado.
Wall Cloud
An isolated lowering of a rain-free cloud base, typically found on the south or southwest side of a supercell. Wall clouds often rotate and may produce a funnel cloud or tornado. They usually precede tornado formation by 10-20 minutes.
Hook Echo
A distinctive hook-shaped radar signature on the right rear of a supercell thunderstorm, indicating rotation and high tornado probability. Hook echoes form as precipitation wraps around the mesocyclone.
Debris Ball
A radar signature showing a concentrated area of debris lofted by a tornado. Debris balls appear as a circular area of high reflectivity collocated with rotation and confirm a tornado is on the ground causing damage.
Watch vs. Warning
A watch means the risk of hazardous weather has risen but its timing, location, or occurrence is still uncertain: be prepared. A warning means hazardous weather is occurring, imminent, or likely and threatens life or property: take action now. An advisory covers events that are occurring or likely but less serious than a warning.
Tornado: Guides and Explainers
These explainers connect this definition to real-world forecasting and decision-making.
In-depth guide
How Tornadoes Form: Types, EF Scale, and Safety
Learn how tornadoes form from supercell thunderstorms, the Enhanced Fujita scale, types of tornadoes, and critical safety steps to protect yourself.
Weather Education
Why Dew Point Matters More Than Humidity
Learn why dew point temperature is a better measure of moisture comfort than relative humidity, how to interpret dew point readings, and when high dew points become dangerous.
Weather Education
What Is a Derecho? The Inland Hurricane Explained
Learn what a derecho is, how it differs from tornadoes and hurricanes, why these long-lived windstorms are so destructive, and how to stay safe when one approaches.
Helpful Tools and Hubs
Use these pages to apply the concept, compare conditions, or follow related weather workflows.
Seasonal Hub
Tornado Season Guide
Peak tornado timing by region, safety planning, and how warnings work.
Feature
Severe Weather
Follow outlooks, watches, warnings, and storm signals in one severe-weather workflow.
Guide
What Causes Thunder and Lightning?
How lightning forms through charge separation, what causes thunder, and how to stay safe.
Guide
Lightning Safety Guide
Know when lightning becomes dangerous, how far away it can strike, and when to move indoors.
Sources
Explore Other Terms
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Small Craft Advisory
A Small Craft Advisory is a National Weather Service alert for winds or seas that are hazardous to small boats in coastal and Great Lakes waters. The wind and sea thresholds are set separately for each geographic area. There is no precise definition of a small craft: any vessel that the conditions could affect counts.
Red Flag Warning
A Red Flag Warning is a National Weather Service alert that weather conditions could cause extreme fire behavior. It is issued when those conditions are occurring or expected within 24 hours. Typical criteria combine dry fuels with sustained winds of 15 mph or more and relative humidity of 25% or less, and exact thresholds vary by state and local office.
El Niño and La Niña
El Niño and La Niña are the warm and cool phases of a recurring climate pattern in the tropical Pacific called the El Niño-Southern Oscillation (ENSO). During El Niño, the trade winds weaken and the central and eastern tropical Pacific runs warmer than average. During La Niña, the trade winds strengthen and the same waters run cooler. Both shift weather patterns worldwide.
Kp Index
The Kp index is a 0 to 9 scale of global geomagnetic activity, reported in 3-hour intervals from ground-based magnetometers. A Kp of 5 or higher indicates a geomagnetic storm, and the values map onto NOAA's G-scale from G1 (Kp 5) to G5 (Kp 9). The higher the Kp, the farther from the poles the aurora can be seen.
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In the WeatherAI App
WeatherAI displays official NWS tornado watches and warnings, and a tornado warning for your current location can appear as a Live Activity on supported iPhones. With Critical Alerts turned on (iPhone and iPad), a tornado warning can sound through silent mode.
Availability, coverage, update frequency, and alert delivery vary by data source, region, subscription plan, device permissions, and service conditions. WeatherAI supplements official sources and is not an emergency notification service. For life-safety decisions, rely on your national weather service, local emergency management, and official warning channels.