US tornado season: quietest start in 60 years

Information released by NOAA’s Storm Prediction Center shows that the US has had its quietest start to the tornado season since detailed records began in 1953.

In 2014, up to 21 April, there have been just 20 tornadoes recorded, which is well below the average of 157 for this point in the season.

There have also been no tornado-related deaths so far this year, which may also be the latest date that this has happened. 

At the other end of the scale, the most active start to the season for the same time period was in 2011, when 465 tornadoes were recorded up to the same date.

US tornado climatology

Tornadoes are spawned by violent, rotating thunderstorms that form due to warm, humid air from the south, colliding with cooler, drier air from the north.

The clash of air with big variations in temperature and humidity fuels super cell thunderstorms, that provide some of the most dangerous weather on the planet.

Although they can occur anywhere, tornadoes are most prevalent in tornado alley in the US, where the flat low-lying central plains offer an ideal breeding ground for severe storms to form and roam for mile after mile.

Statistics show that around 1,200 tornadoes affect the US each year, with peaks occurring along the Gulf coast earlier in spring, shifting to the southern plains from May to June, before reaching the northern plains and Midwest in June and July.

Why so quiet this year?

As I mentioned already, tornadoes are caused by severe thunderstorms, driven by the clashing of warm, moist air and cooler, drier air.

However, the winter that the US experienced this year was very cold, with central and eastern parts of the country firmly in the grip of below normal temperatures.

Due to this colder, drier air lingering well into spring, the usual push northwards of warm, humid air from the Gulf hasn’t really been as marked.

This has led to fewer and less severe thunderstorms, which in turn has significantly lowered number of tornadoes occurring.

Despite the quite start to the season, many places have yet to reach their peak periods, which means that there is still plenty of time for severe weather outbreaks and tornadoes to occur.

In fact, the US National Weather Service is warning that there is a risk of severe thunderstorms and tornadoes in the next 24 hours, from Texas to Nebraska.

I’ll be keeping a close eye on the potential storms and will post updates on Twitter – @liamdutton