TL;DR

The Enhanced Fujita (EF) Scale rates tornadoes from EF0 to EF5 based on the damage they cause to buildings, trees, and other structures — not by measuring wind speed directly inside the funnel. National Weather Service survey teams examine damage indicators after a tornado and estimate the wind speed required to produce that damage. EF5 tornadoes are exceptionally rare because they require near-total destruction of well-built structures.

What is the Enhanced Fujita Scale?

The Enhanced Fujita Scale is the standard system used by the National Weather Service to classify tornado intensity in the United States. Introduced on February 1, 2007, the EF-Scale replaced the original Fujita Scale (F-Scale) developed by Dr. Ted Fujita in 1971.

Both scales rate tornadoes from 0 to 5, but the EF-Scale refines the wind speed estimates and expands the range of damage indicators surveyors use to assign ratings. The goal is a more accurate and consistent assessment of tornado strength based on observable damage.

The EF-Scale does not measure wind speed directly. Anemometers and weather stations are rarely positioned in a tornado's path, and even when they are, the instruments often fail before recording peak winds. Instead, the NWS sends survey teams into affected areas after a tornado to document what was damaged and how severely.

How do surveyors assign an EF rating?

After a tornado, NWS meteorologists walk or drive through the damage path, photographing destroyed homes, uprooted trees, overturned vehicles, and damaged infrastructure. They compare what they observe to a set of 28 damage indicators — categories of structures and objects that respond predictably to wind.

Each damage indicator has multiple degrees of damage, ranging from minor cosmetic harm to complete destruction. For example, one damage indicator is "one- or two-family residence." The degrees of damage for that indicator range from "threshold of visible damage" (a few shingles missing) to "total destruction of engineered building" (the house is reduced to a bare foundation).

The NWS uses engineering studies and wind tunnel research to estimate the wind speed required to produce each degree of damage for each indicator. Surveyors identify the most intense damage they can confidently attribute to tornadic winds, then assign the corresponding EF rating.

A tornado receives the highest rating supported by the damage evidence. If a tornado destroys a poorly anchored mobile home but leaves a nearby well-built house with only roof damage, the rating reflects the well-built house, not the mobile home. This approach reduces bias from structures that are unusually vulnerable or resistant to wind.

What does each EF rating mean?

The Enhanced Fujita Scale has six categories. The wind speeds listed are three-second gust estimates — the peak wind speed sustained for three seconds at the point of damage.

  • EF0: 65–85 mph. Minor damage. Shingles and siding torn off, branches broken, shallow-rooted trees pushed over.
  • EF1: 86–110 mph. Moderate damage. Roofs partially removed, windows broken, mobile homes overturned or badly damaged.
  • EF2: 111–135 mph. Considerable damage. Roofs torn off frame homes, large trees snapped or uprooted, mobile homes destroyed, cars lifted off the ground.
  • EF3: 136–165 mph. Severe damage. Entire stories of well-constructed homes destroyed, trains overturned, most trees in a forest uprooted.
  • EF4: 166–200 mph. Devastating damage. Well-built homes leveled, structures with weak foundations blown away, cars thrown considerable distances.
  • EF5: Over 200 mph. Incredible damage. Strong frame homes swept clean from foundations, steel-reinforced concrete structures badly damaged, vehicles thrown over 100 yards, bark stripped from trees.

The NWS emphasizes that these wind speeds are estimates, not measurements. Two tornadoes with identical EF3 ratings may have had different actual wind speeds, depending on what structures were available to damage.

Why are EF5 tornadoes so rare?

Since the EF-Scale was introduced in 2007, only eight tornadoes in the United States have been rated EF5. The most recent was the Moore, Oklahoma tornado on May 20, 2013. By comparison, dozens of EF0 and EF1 tornadoes occur every year.

EF5 damage requires extraordinary wind speeds and a direct hit on a well-built structure. Many tornadoes track through rural areas where few engineered buildings exist. If a violent tornado destroys only barns, trees, and poorly anchored homes, surveyors may have no evidence to support a rating higher than EF3 or EF4, even if the tornado was capable of EF5 winds.

The rarity of EF5 ratings also reflects improved building codes and construction practices in some regions. Modern homes with proper roof-to-wall connections and reinforced foundations are more resistant to wind damage than older structures, which can result in lower ratings for tornadoes of similar strength.

Finally, the EF-Scale is conservative by design. Surveyors assign the rating that the damage supports, not the rating the tornado might have achieved under different circumstances. If the evidence is ambiguous, the lower rating is chosen.

How does the EF-Scale differ from the original Fujita Scale?

Dr. Ted Fujita introduced the original F-Scale in 1971 as a way to estimate tornado wind speeds from damage. The F-Scale used the same 0-to-5 structure, but its wind speed ranges were based on theoretical calculations rather than empirical engineering data.

By the early 2000s, researchers recognized that the F-Scale overestimated wind speeds, particularly at the upper end. An F3 tornado on the original scale was thought to have winds of 158–206 mph, but engineering studies showed that the observed F3 damage typically required winds closer to 136–165 mph.

A committee of meteorologists and engineers convened by the Wind Science and Engineering Research Center at Texas Tech University developed the Enhanced Fujita Scale to address these issues. The EF-Scale:

  • Adjusted wind speed ranges to align with modern engineering research.
  • Expanded the list of damage indicators from a handful to 28, covering a wider variety of structures.
  • Introduced degrees of damage for each indicator, allowing for more granular assessments.
  • Improved consistency across different survey teams and regions.

The EF-Scale took effect on February 1, 2007. All tornadoes rated after that date use the EF designation. Tornadoes before 2007 retain their original F ratings — for example, the May 3, 1999 tornado that struck Moore, Oklahoma is still referred to as an F5.

Why doesn't the NWS measure tornado wind speeds directly?

Measuring wind speed inside a tornado is extraordinarily difficult. Tornadoes are unpredictable, short-lived, and capable of destroying most instruments. Mobile Doppler radar units can estimate wind speeds from a distance, but they measure winds aloft, not at ground level where damage occurs.

In rare cases, hardened weather stations or specialized research instruments have recorded wind speeds near or inside tornadoes. During the May 3, 1999 Bridge Creek–Moore tornado, a mobile Doppler radar measured winds of 301 mph above the ground — the highest wind speed ever recorded in a tornado. But such measurements are exceptions, not the rule.

The damage-based approach of the EF-Scale provides a practical, repeatable method that works for every tornado, regardless of whether instruments were present. It also reflects what matters most to communities: not the abstract wind speed, but the tornado's impact on people and property.

What should you do if a tornado warning is issued?

Tornado intensity cannot be predicted before a tornado forms. A warning may be issued for a storm capable of producing an EF0 or an EF5 — the NWS does not differentiate in the warning text. Every tornado warning should be treated as a life-threatening event.

When a tornado warning is issued:

  • Move immediately to the lowest floor of a sturdy building.
  • Get into an interior room or hallway, away from windows.
  • Cover yourself with a mattress, heavy blankets, or a helmet to protect against flying debris.
  • If you are in a mobile home, evacuate to a nearby permanent structure or storm shelter.

Most tornado fatalities occur in mobile homes or vehicles. If you live in a mobile home and a tornado warning is issued at night, you need a way to wake up. Outdoor sirens are not designed to be heard indoors, and many smartphone weather apps are silenced by Do Not Disturb. Wireless Emergency Alerts for tornado warnings break through Do Not Disturb on most phones by default, but third-party weather apps do not.

VORTEX is a free web app at vortexintel.app that monitors severe weather nationwide. Pro ($4.99/month) places phone calls to your phone when a tornado or flash flood warning is issued for a location you care about — calls can ring through Do Not Disturb once you enable Emergency Bypass for the number, unlike most third-party app notifications.