Since 2013, there has been a drought of the strongest tornadoes on the Enhanced-Fujita scale. The last EF-5 occurred on May 20, 2013.

The U.S. is currently experiencing the longest EF-5 drought in recorded history. The last EF-5 tornado happened in Moore, Okla., on May 20, 2013, meaning it's been nearly 12 years since a tornado was rated an EF-5, despite very active weather showing up on the WeatherRadar.

The EF scale, short for Enhanced Fujita Scale, is used to classify tornadoes based on the damage they cause and the estimated wind speeds associated with that damage. It ranges from EF0 (least damaging) to EF5 (most damaging). This scale was developed to replace the original Fujita Scale and became operational on February 1, 2007. 

So why are we seeing a drought of the strongest tornadoes? One study suggested that the stricter use of the EF scale's damage indicators, compared to the older Fujita scale, may be the reason for the decline in EF5 ratings.

The EF scale's criteria, particularly for single-family homes, are based on engineering principles. A well-constructed home being swept off its foundation is now categorized as EF4 damage, whereas the previous Fujita scale would have classified it as F5.

A drought of EF-5 tornadoes doesn't mean that storms are becoming safer; instead, how we rate tornado damage has changed. Stay weather-aware and turn your Weather & Radar app alerts on when severe weather is forecast.