EF5 tornadoes are extremely violent and often ravage large swathes of territory. However, this is the first time in history that we've gone so long without seeing the shadow of such a phenomenon...
The last EF5 tornado to be observed in the USA dates back to 2013. Winds were reported to have reached 337 km/h. The town of Moore, nearOklahoma City, was completely devastated: over 1,000 homes destroyed, 26 deaths and millions of dollars in damage were recorded as a result of this event. It occurred on May 20. It will be 10 years to the day in a few days...
Since then, radio silence.
This is the first time that the break between two tornadoes of this strength has been so long since NOAA began collecting data over 70 years ago, in the 1950s. The previous sequence was between May 1999 and May 2007.
Good to know: Tornado strength is assessed by the damage recorded in the field. It ranges from EF0 to EF5, according to the improved Fujita scale.
|EF0||105-137||Light||A few pieces of roof covering removed (tile, asphalt shingles, etc.), damage to gutters, chimneys and siding, broken branches, overturned trees with surface roots|
|EF1||138-178||Moderate||Roof coverings completely removed, mobile homes overturned or severely damaged, exterior doors blown off, windows and other glass items broken.|
|EF2||179-218||Considerable||Roofs blown off well-built houses, light-frame houses displaced from their foundations, mobile homes completely destroyed, large trees broken or uprooted, light objects turned into projectiles, automobiles lifted.|
|EF3||219-266||Severe||Entire floors of solid houses destroyed, major damage to public buildings such as shopping malls and business centers, trains overturneds, debarked trees, trucks and large cars lifted and moved, light buildings completely blown away.|
|EF4||267-322||Devastators||Well-built and light-frame houses destroyed, cars blown away at a distance and numerous objects turned into projectiles.|
|EF5||> 322||Incredible||Solid houses razed to the ground and debris hurled, car-sized objects hurled more than 100 meters, skyscrapers with structural damage, etc.|
All the indications are that the respite could be even longer: conditions, both aloft and towards the surface, are not conducive to this type of tornado at the moment.
Tornado activity is highly variable from one year to the next. For example, between May 2007 and May 2013, nine EF5 tornadoes were observed across the United States. Then, nothing. Prior to this period, it had also been quiet since 1999.
Tornadoes and global warming: how are they changing?
Since the 1950s, the trend in the number and frequency of tornadoes in the USA has been downward. This is undoubtedly due to global warming, which is reducing the horizontal thermal contrasts between the north and south of the North American continent.