DETERMINING THE STRENGTH OF TORNADOES
Since the beginning of 2023, more than 300 tornadoes have been reported across the U.S. A tornado, a ferocious rotating column of air that descends from a thunderstorm to the ground, is considered one of the most violent weather phenomena in nature. They are powerful, destructive, and sometimes deadly. When tornadoes are in the forecast, AccuWeather For Business provides 16 minutes of advance notice compared to an average of 8 minutes from other sources.
A tornado's strength is rated on the Enhanced Fujita Scale or EF Scale. Weather experts started using this scale in February 2007 to assign each tornado a rating based on tornado-related damage it caused and estimated wind speed. Each tornado is rated from EF0 - EF5, with EF0 being the weakest and EF5 being the strongest. The EF Scale replaced the F Scale previously used.
Each rating is determined by surveying the damage it causes and comparing it based on the degree of damage. The EF Scale considers more variables and provides a better overall wind speed estimate due to the associated storm damage than the original F Scale. That's because it looks at 28 damage indicators such as trees, building types, and structures, according to Guy Pearson, AccuWeather’s Director of Weather Warning Service. The scale also considers wind speeds required to observe the damage and assigns a corresponding EF rating based on that damage. However, the EF-Scale only measures the intensity of a tornado and not its size or duration.
Who determines the rating?
The National Weather Service sends a team to survey the damage immediately. If a tornado happens in the morning, they try to have a team surveying by the afternoon. It usually takes the NWS team to survey and have a preliminary rating in one to two days. Sometimes it can take longer if there is a tornado outbreak. That's because not only does the team need to travel to the impacted site and do the survey, but they also have to analyze all of the data and publish the preliminary report across multiple dissemination methods.
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>>READ MORE: When minutes matter: how to plan for and respond to a SkyGuard Tornado Warning