Insights & News

Severe Thunderstorm Climatology Outside the USA

5th May 2020

In the previous blog entry, I took a close look at how and why US thunderstorms and tornadoes have been observed to reach intensities that have never (reliably) been observed elsewhere on the planet.

This one casts an eye over six broad regions: Europe, Asia, the tropics, Oceania and South America. Yes, most of the world!

There is generally less familiarity with tornado climatology outside of the USA, so I have decided to place additional focus on those here. I hope you enjoy reading this as much as I enjoyed researching for it (a lot)!

 

Europe

This continent is no stranger to severe thunderstorms, but very rarely do they become comparable to the strongest US storms.

In the UK and north-sea borderlands of France to Germany, tornadoes are frequent but mainly weak (F0 to F2 intensity). Only a few are associated with supercells – those tending to be the strongest. In records back to 1764, there are four tornadoes rated EF5 equivalent, but only one is within the last 100 years (Jun 24th 1967 near Palluel, France) and its rating has yet to be fully validated.

The main limitation on supercell development is the positioning of major mountain ranges. Instead of being in the west and orientated north-south, they’re in the south and orientated west-east.

There’s also not much in the way of high plains suitable for the production of hot-dry mid-level air. One of the largest is Spain’s high central plateau. This is the source of the ‘Spanish Plume’ events known for bringing particularly hot spells of weather to north-western Europe. These often go out ‘with a bang’, producing some of the strongest thunderstorms seen the region.

Map with annotations summarising the severe thunderstorm climatology of Europe

In Scandinavia, mountains in the west can facilitate an environment across central Scandinavia that’s conducive to tornadic supercells. In summer, surface heating is occasionally strong enough to trigger such an event. A 2005 study by J. Teittinen (A climatology of tornadoes in Finland) documented 30 strong tornadoes between 1796 and 2003 (and 121 weak ones). None reached EF5 intensity.

Elsewhere in Europe, tornadoes are rare, likely averaging 5-15 per year in most countries (based on estimates by Nikolai Dotzek in 2003; An updated estimate of tornado occurrence in Europe). Even so, thunderstorms do occasionally reach extreme ferocity. For example, an officially rated EF5 is reported to have partially levelled a large stone monastery at Treviso, Udine, Italy on 24th July 1930.

Non-Tropical Asia

If they were less mountainous, Japan & north-eastern China would likely be capable of producing tornadic supercells on par with the largest observed in the USA during most years. Even with that handicap, several tornadoes of F3 intensity have been documented, along with one F4 event in Japan.

Elsewhere in this vast region, tornadoes are generally weak (F0 to F2). Many are associated with tropical cyclones. Some begin as waterspouts before moving inland, making for an exciting but sometimes damaging spectacle (winds may reach over 100 mph).

A striking exception is north-eastern India and Bangladesh. Here, the springtime build of surface heat often leads to very strong temperature gradients against cool air aloft associated with the Himalayas. This can support large supercell development with strong tornadoes capable of taking many lives in these densely populated regions. On 17th April 1973, a single tornado in the Dhaka Division of Bangladesh caused a staggering 681 fatalities.

Map with annotations summarising the severe thunderstorm climatology of non-tropical Asia

The Tropics

Powerful surface heating is readily available and thunderstorm development is an almost daily occurrence.

But, their severity is usually limited by warm and moist air extending to a great height above the surface.

Occasionally, though, an area of cool air aloft moves in from outside the tropics and this can trigger some of the largest, most severe thunderstorms seen outside the USA.

Tropical tornadoes are mostly associated with tropical cyclones interacting with non-tropical weather fronts. This produces a combination of strong rising motion and wind shear, which is very conducive to rotating funnel development. The associated thunderstorms rarely develop into supercells, though, so these tornadoes tend to be brief and at the low end of the scale (but still destructive!).

Non-Tropical Oceania

In Australia, there’s not much high terrain to facilitate hot, dry inversions. Despite this, tornadic supercells do sometimes develop – mainly in New South Wales, southern Queensland and southern Western Australia. They can pack a punch, but no reported tornado has ever exceeded F3 intensity.

For New Zealand, meanwhile, the issue is mainly one of size. Being tall and skinny doesn’t lend itself well to developing tornadic supercells. Nor does having no large areas of high terrain to your west. As a result, tornadoes are mainly weak (F0 to F2), narrow and short-lived ones associated with non-supercell thunderstorms.

Map with annotations summarising the severe thunderstorm climatology of non-tropical Oceania

Non-Tropical Southern Hemisphere Africa

Tornadoes do develop here but tend to be weak (F0 to F2) and short-lived – mainly due to a lot of high, rugged terrain keeping supercell structures relatively small. Exceptions do occur, though, most notably an F3 tornado reported 50 km south of Johannesburg in 1999. That same year, a tornado struck the town of Umtata while South African President Nelson Mandala was visiting his local pharmacy! His bodyguards lay on top of him as protection while the tornado took the lives of 11 townspeople and injured 150 others.

Map with annotations summarising the severe thunderstorm climatology of non-tropical Southern Hemisphere Africa

Non-Tropical South America

The last in my least but far from the least. Like the USA, it has a large, north-south orientated mountain range situated to the west of a large expanse of relatively flat, low-lying land. It also has a reliable source of warm, moisture-laden air (tropical rainforests to the north).

These ingredients combine most effectively over the Pampas region of South America. It’s the closest rival to the US Central Great Plains when it comes to supporting large supercell development.

Map with annotations summarising the severe thunderstorm climatology of non-tropical South America

22nd Nov 1951, a tornado reportedly derailed an Argentine train while it was transporting some 600 passengers from Rosario to Tucuman. It’s conceivable that this was of EF5 intensity. Tornado reporting in the region is of poor quality, so I’d not be surprised to learn of several such events in the past century.

Southern Brazil is also no stranger to tornadoes, though conditions tend not to be quite so conducive. Most notably in recent years, a multi-vortex F3-rated tornado rampaged across São Paulo State on 24th May 2005.

 

That concludes this world-spanning roundup of tornado climatology outside the USA. I hope it hasn’t left your head in a spin!

James Peacock MSc
Head Meteorologist at MetSwift

P.S. Most of the example statistics I have used were sourced within an impressive collection of regional summaries accessible on islandnet.com, which I can highly recommend exploring if you would like to delve into tornado climatology further.

Featured Image by Unknown Author is licensed under CC BY-NC

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