How Tornadoes Form and How to Stay Safe When One Hits

Quick Answer

Tornadoes form when colliding air masses create rotating updrafts within severe thunderstorms, typically during spring and summer in the central United States. The Enhanced Fujita Scale rates tornadoes from EF0 (65-85 mph winds) to EF5 (over 200 mph), with damage severity determining the final rating.

Staying safe requires monitoring National Weather Service alerts, understanding warning terminology, and having a plan for seeking shelter in a basement or interior room away from windows.

Key Facts

• The U.S. recorded 1,558 tornadoes in 2025, compared to 1,910 in 2024 and the 15-year historical average of 1,392.
• Tornadoes caused 68 fatalities in the U.S. in 2025, up from 54 in 2024.
• Texas (162), Illinois (146), Missouri (120), Mississippi (111), and Alabama and North Dakota (72 each) recorded the most tornadoes in 2025.
• The Enhanced Fujita Scale assigns ratings based on estimated wind speeds and related damage: EF0 (65-85 mph), EF1 (86-110 mph), EF2 (111-135 mph), EF3 (136-165 mph), EF4 (166-200 mph), and EF5 (over 200 mph).
• A tornado that fails to impact any ratable structures receives an EF-Unknown (EF-U) rating.
• The March 14-15, 2025 outbreak produced over 100 tornadoes, including three EF4s and 11 EF3s, with the most violent rated EF4 at 190 mph.
• On June 20, 2025, an EF5 tornado struck Enderlin, North Dakota, with winds exceeding 210 mph, ending a 12-year period without an EF5-rated tornado in the U.S.
• The EF5 tornado carved a path 12.1 miles long and up to 1.05 miles wide.

The Recipe for a Tornado What Conditions Must Align

Understanding tornado formation begins with recognizing that tornadoes do not simply appear from any thunderstorm. They require a specific combination of atmospheric ingredients that, when present together, create the potential for violent rotating columns of air to reach the ground.

The Collision of Air Masses

The central United States provides the ideal geographic stage for tornado development because it sits at the meeting point of contrasting air masses. Warm, moist air flows northward from the Gulf of Mexico, while cool, dry air pushes southward from Canada and the Rocky Mountains.

When these two air masses collide, the denser cool air forces the warm, moist air upward, creating the instability that fuels severe thunderstorms. This collision typically occurs along what meteorologists call a dry line or a cold front.

The boundary between these air masses creates lift, and the warm air's moisture provides the energy source for thunderstorm development. Without this contrast, the atmosphere remains too stable for the violent updrafts that tornadoes require.

Wind Shear The Rotation Engine

Temperature and moisture differences alone produce ordinary thunderstorms, not tornadoes. The critical additional ingredient is wind shear, which refers to changes in wind speed and direction with height.

When winds at the surface blow from the south while winds higher in the atmosphere blow from the west or southwest, the atmosphere begins to rotate horizontally. Think of a rolling pin lying on its side.

Thunderstorm updrafts can tilt this horizontal rotation vertically, transforming it into a rotating column of air within the storm. This rotating updraft, called a mesocyclone, typically spans two to six miles in diameter.

Most severe thunderstorms that produce tornadoes contain a mesocyclone, though only a fraction of mesocyclones actually produce a tornado. The process of a tornado touching down involves further intensification of rotation in a smaller area near the base of the storm.

The Role of the Supercell

Most significant tornadoes come from a specific type of thunderstorm called a supercell. Supercells are distinguished by their persistent, rotating updraft that can last for hours.

This longevity allows the storm to maintain its structure and continue producing severe weather over a prolonged period. Supercells typically develop in environments with strong wind shear and significant atmospheric instability.

The rotating updraft within a supercell can produce large hail, damaging winds, and tornadoes. The March 14-15, 2025 outbreak demonstrated the destructive potential of supercells, producing over 100 tornadoes across multiple states with three rated EF4 and 11 rated EF3.

Why Some Storms Produce Tornadoes and Others Do Not

Meteorologists continue to study why some supercells produce tornadoes while others never do. The exact trigger that causes rotation to tighten and descend to the ground remains an area of active research.

Factors that appear to contribute include the strength of the updraft, the amount of low-level wind shear, and the thermodynamic profile of the atmosphere near the ground. What is clear is that tornado formation requires a delicate balance.

Too little wind shear and the storm lacks rotation. Too much instability without proper shear and the storm produces intense rainfall or hail but not organized rotation.

The most violent tornadoes, those rated EF4 and EF5, require particularly favorable conditions that occur relatively rarely, which helps explain why EF5 tornadoes are so uncommon.

The 2025 Season A Year of Extremes

The 2025 tornado season provided a stark illustration of both the frequency and the destructive potential of tornadoes across the United States. With 1,558 tornadoes reported, the year marked the second consecutive year with above-average activity, following 2024's preliminary total of 1,910.

The March Outbreak A Historic Event

The most significant tornado event of 2025 occurred on March 14-15, when a massive storm system swept across the central and southern United States. This outbreak produced over 100 tornadoes, including three rated EF4 and 11 rated EF3.

The most violent tornado of this event was rated EF4 with winds estimated at 190 mph. This outbreak demonstrated how tornado activity can spike dramatically within a short window.

The Storm Prediction Center had issued a Day 1 Convective Outlook on March 14, 2025, indicating the potential for severe weather. The resulting tornadoes caused widespread damage and multiple fatalities across several states.

The March outbreak also highlighted the challenges of nighttime tornadoes. Storm chasers who documented the event noted the difficulty of tracking tornadoes in darkness, a factor that can increase danger because residents may not see the approaching storm.

The Enderlin EF5 Ending a Long Drought

Perhaps the most notable single tornado of 2025 was the EF5 that struck near Enderlin, North Dakota, on June 20. This tornado tore a 12.1-mile path of destruction up to 1.05 miles wide through southeast North Dakota.

Initial assessments by the National Weather Service suggested a high-end rating, and the tornado was subsequently upgraded to EF5 with winds exceeding 210 mph. This rating was significant because it marked the first EF5 tornado in the United States in 12 years.

EF5 tornadoes are extraordinarily rare, representing only about 0.2% of all tornadoes in the historical record since 1680. The confirmation of this rating required assistance from researchers at Western University's Northern Tornadoes Project, who helped analyze the damage patterns.

The Enderlin tornado demonstrated that EF5-strength tornadoes remain possible even in regions not traditionally associated with the most violent tornadoes. While the Great Plains and Southeast typically see the majority of tornado activity, this event showed that extreme tornadoes can occur across a wider geographic range.

Geographic Shifts in Tornado Activity

The 2025 data revealed notable shifts in where tornadoes occurred compared to previous years. Texas led the nation with 162 tornadoes, consistent with its size and location in the traditional Tornado Alley region.

However, the presence of Illinois (146), Missouri (120), and Mississippi (111) in the top five indicated increased activity in the mid-South and Midwest. Compared to 2024, Florida, Iowa, and Nebraska dropped out of the top five, while Mississippi, Alabama, and North Dakota entered the rankings.

This shift reflected an overall decrease in tornadoes along the East Coast and an increase in a narrow strip of land across the eastern half of the country. The 2025 season also saw significant tornado activity outside the United States.

A tornado in Ninh Binh, Vietnam, killed 9 people in September, while a powerful tornado in Brazil in November killed at least 6 and injured hundreds. Typhoon-related tornadoes in Vietnam and Taiwan added to the global toll, demonstrating that tornadoes remain a worldwide hazard.

Understanding Tornado Ratings and What They Mean

The Enhanced Fujita Scale, operational since February 1, 2007, provides the framework for classifying tornado intensity. Understanding this scale helps the public interpret warnings and appreciate the varying levels of danger different tornadoes present.

How the Enhanced Fujita Scale Works

The EF Scale assigns ratings based on estimated wind speeds and the damage those winds cause. Meteorologists examine damage indicators, such as how structures are affected, and estimate the wind speeds required to produce that level of destruction.

The scale ranges from EF0 to EF5:

• EF0 (65-85 mph): Light damage. Some damage to chimneys and branches; shallow-rooted trees pushed over.
• EF1 (86-110 mph): Moderate damage. Roofs severely stripped; mobile homes overturned; moving cars pushed off roads.
• EF2 (111-135 mph): Significant damage. Roofs torn off well-constructed houses; mobile homes destroyed; boxcars overturned.
• EF3 (136-165 mph): Severe damage. Entire stories of well-constructed houses destroyed; trains overturned; cars lifted and thrown.
• EF4 (166-200 mph): Devastating damage. Well-constructed houses leveled; cars thrown considerable distances.
• EF5 (over 200 mph): Incredible damage. Strong frame houses leveled off foundations and swept away; automobile-sized missiles thrown.

Tornadoes that fail to impact any ratable structures receive an EF-Unknown (EF-U) rating. This can occur when a tornado touches down in open countryside without damaging buildings or other structures that would allow meteorologists to estimate wind speeds.

The Rarity of Extreme Ratings

The historical data shows a dramatic decrease in frequency as ratings increase. EF0 tornadoes account for approximately 40.1% of all tornadoes since 1680, while EF1 tornadoes represent 31.8% and EF2 tornadoes 19.6%.

The percentages drop sharply for the most violent categories: EF3 tornadoes represent about 6% of the total, EF4 tornadoes about 2.2%, and EF5 tornadoes a mere 0.2%. This distribution means that the vast majority of tornadoes cause relatively limited damage, but the small percentage of violent tornadoes account for a disproportionate share of fatalities and destruction.

The March 2025 outbreak's three EF4 tornadoes and 11 EF3 tornadoes represented exactly the kind of event that can cause widespread devastation.

The Difference Between Original and Enhanced Scales

The original Fujita Scale, introduced in 1971, used a similar six-category structure but with different wind speed estimates. The original F0 covered 40-72 mph, while the enhanced EF0 starts at 65 mph.

The original F5 ranged from 261-318 mph, while the enhanced EF5 simply indicates winds over 200 mph. The Enhanced Fujita Scale was developed partly because the original scale's wind speeds were considered unreliable, particularly for the highest categories.

The EF Scale uses more detailed damage indicators and accounts for construction quality, making ratings more consistent and scientifically defensible.

How to Stay Safe When a Tornado Threatens

Preparation and quick action can mean the difference between life and death when a tornado approaches. Understanding the warning system and having a plan before severe weather strikes are the most effective safety measures.

Understanding Tornado Watches and Warnings

The National Weather Service issues two primary types of alerts. A tornado watch means conditions are favorable for tornado development and residents should be prepared to act quickly if a warning is issued.

A tornado warning means a tornado has been spotted or indicated on radar and immediate action is necessary. The most urgent alert is a Tornado Emergency, which is issued only in rare situations when a violent tornado is confirmed and is expected to cause catastrophic damage.

This elevated warning is reserved for situations where the threat is both imminent and extreme. When a warning is issued, the time to act is immediate.

Tornadoes can move quickly, and the window between warning issuance and tornado arrival can be just minutes. Having a plan in place beforehand eliminates the need for decision-making during a crisis.

Where to Shelter

The safest location during a tornado depends on the type of building. In a house with a basement, the basement provides the best protection, particularly a corner away from windows.

In homes without basements, the smallest, most interior room on the lowest floor, such as a bathroom or closet, offers the best available protection. Mobile homes are extremely vulnerable to tornado damage.

Residents should leave mobile homes and seek shelter in a designated storm shelter or the nearest substantial building. The EF Scale ratings for destroyed mobile homes begin at EF1, meaning even relatively weak tornadoes can destroy these structures.

During the March 14-15, 2025 outbreak, families who survived often credited pre-planned shelter locations. Reports from the aftermath described how having a designated safe room allowed families to gather quickly when warnings were issued.

What to Include in a Tornado Safety Kit

A basic tornado safety kit should include a weather radio with battery backup, bottled water, a first aid kit, flashlights with extra batteries, and sturdy shoes to protect against debris. Important documents should be stored in a waterproof container that can be grabbed quickly.

For those in tornado-prone areas, helmets can provide additional protection against head injuries from falling debris. While no helmet can protect against all tornado forces, they can reduce the severity of injuries from smaller impacts.

After the Tornado Passes

The danger does not end when a tornado lifts. Downed power lines, broken gas lines, and damaged structures create ongoing hazards.

Residents should avoid entering damaged buildings until officials declare them safe, and should watch for debris that may be hidden in yards or streets. The aftermath of the Enderlin EF5 demonstrated the extensive damage even a single tornado can cause.

With a path over a mile wide, the tornado affected a substantial area, and recovery took considerable time. Understanding that recovery is a process can help communities prepare for the long-term impacts of significant tornado events.

Frequently Asked Questions

What is the difference between a tornado watch and a tornado warning?

A tornado watch means conditions are favorable for tornado development in the watch area, and residents should be prepared to act. A tornado warning means a tornado has been spotted or indicated on radar, and residents in the warned area should seek shelter immediately.

A Tornado Emergency is a more urgent warning issued only for confirmed violent tornadoes expected to cause catastrophic damage.

Can tornadoes occur outside the traditional "Tornado Alley"?

Yes. While the central United States sees the most tornado activity, tornadoes have occurred in every state.

In 2025, the top five states for tornado counts were Texas, Illinois, Missouri, Mississippi, and Alabama and North Dakota. The June 2025 EF5 in North Dakota demonstrated that even extreme tornadoes can occur outside the traditional Tornado Alley region.

How is a tornado's EF rating determined?

The Enhanced Fujita Scale rating is based on estimated wind speeds and related damage. Meteorologists examine damage indicators, such as how structures are affected, and estimate the wind speeds required to produce that damage.

Tornadoes that do not impact any ratable structures receive an EF-Unknown rating.

How common are EF5 tornadoes?

EF5 tornadoes are extremely rare, representing about 0.2% of all tornadoes in the historical record. The June 20, 2025 tornado near Enderlin, North Dakota, was the first EF5 in the United States in 12 years.

For comparison, EF0 tornadoes represent about 40.1% of all tornadoes.

What should I do if I am driving when a tornado warning is issued?

Do not try to outrun a tornado in a vehicle. If a tornado is visible and approaching, seek shelter in a substantial building if one is available.

If no building is accessible, the recommended course is to stay in the vehicle with the seatbelt fastened and cover your head, or find a low-lying area away from the vehicle and lie flat, covering your head. Mobile homes and vehicles offer little protection from tornadoes.

Reference Notes

Information in this article is based on publicly available sources. Some details may change over time.

Verify with official sources before acting.