A Recent Plains Tornado Was Rated EFU. You Read That Right – Here's What It Means

Here's a look at cases when this lesser-known tornado rating is used by the National Weather Service.

February 26,2025

New Study Reveals The Lack Of EF5 Tornadoes

Tornado ratings are commonly assigned after severe weather strikes,but there's one type of classification you might not have heard of before:the so-called EFU tornado,as we saw recently in South Dakota.

Big Picture:Tornadoes Are Rated On The Enhanced Fujita Scale

They usually range from EF0 (light damage) to the rare EF5 (incredible damage),based on the most severe damage they cause along their path,not by their appearance or any other real-time metric such as Doppler radar.

The tornado wind speeds for those ratings are estimated through damage inspections performed by the National Weather Service (NWS) after the storm. Factors weighed include the quality of building construction and other types of damage,from trees to small barns to large shopping centers.

(MORE:How Surveys Reveal A Tornado's Strength)

The scale ranks tornadoes based on estimated wind speed from the damage they cause. — Wind speeds associated with tornado damage on the Enhanced Fujita Scale.

Deeper Dive:EFU Rating Is An Oddball Exception

But what happens when a tornado is spotted and there is no damage to survey? That's where the EFU rating comes into play,where U stands for "unknown."

A prime example happened Feb. 24 in South Dakota,when a brief tornado documented by a storm chaser spun up over an open field. An assessment by the NWS said it caused no damage and assigned the twister an EFU rating,making it the state's first February tornado on record.

It's likely this tornado's winds were on the weaker end of the spectrum along the lines of an EF0 (65 to 85 mph winds),but since there was no visual damage to inspect,that rating can't be used.

(MORE:South Dakota's First February Tornado)

The EFU tornado on Feb. 24,2025,was located in eastern South Dakota near the borders between Codington,Hamlin,and Deuel counties. It lasted a minute. — The EFU tornado on Feb. 24,2025,was located in eastern South Dakota near the borders between Codington,Hamlin and Deuel counties. It lasted a minute.

Geek Out More:The Rating Has Been Used In Practice Nearly 10 Years

The EFU rating category was around before 2013 but wasn't used in practice until 2016,according to a recent paper by NOAA meteorologists.
Other reasons tornadoes can have an EFU rating include ones that occur in such a remote setting that they cannot be surveyed,or damage indicators are of a type that's not standard to what's used in the scale.
Many of the EFU tornadoes are in the Plains or Midwest states where there are fewer structures and trees for tornadoes to hit and cause damage that can be rated by an NWS survey team.

Chris Dolce has been a senior digital meteorologist with www.weathernow24.com for nearly 15 years after beginning his career with Weather Now 24 in the early 2000s.