Frequency of tornadoes outside of the USA

[Patty O'Furniture]

I don't think I've ever heard a weatherman talk about a tornado that ripped through, say, Norway (laying waste to all trailer parks in its path, of course).

Is the US especially prone to tornado formation? Do people in other countries hear about our F5 whoppers on their six o'clock news? Tornadoes are much more spectacular than earthquakes or forrest fires, so I would think that when an F4 or better touches down anywhere, everybody should be talking about it.

[Arjuna34]

There's a good discussion of this question in this old GQ thread:

Tornadoes native only to USA?

Arjuna34

[AWB]

The DC area just got hit with tornados. But I never heard of tornados east of Kansas when I grew up in Colorado. Maybe they were just local-level stories.

[cw]

I don't know about other countries and tornados, I'm sure they have them elsewhere. Being from Oklahoma though, the midwest of the U.S. is more prone to tornados than any other place on earth. Here they are very much a common occourance in spring and summer.

[Astroboy14]

Oddly enough, here in Korea there was a small tornado just recently (maybe in the past month or so?)... no on was hurt, as I recall, but some trees were ripped up and I think a house or two lost roofs... I tried to find an article about it to link to, but no luck!

FTR, tornados are VERY rare here...

[Mangetout]

We get tornadoes here in the UK (apparently alomst a daily event - I don't have a cite for that at the mo, but I'll find one if necessary)

But they are seldom big enough or long-lived to do much serious damage (maybe a few houses lose their roof) and they often occur over the sea. - they are never anything like the scale of the ones you get in the US.

[ticker]

To add to what Mangetout said, I heard somewhere (again no cite) that the UK had the highest number of tornadoes, relative to it's area, of any country. However a really big, newsworthy tornado might lift a few tiles from a roof. British cows are not in danger of being blown across several counties which is just as well with foot-and-mouth restrictions on livestock movement.

[Wumpus]

Which leads to another question ... what's the minimum siz/wind speed required to qualify as a tornado? Presumably lil' dust devils don't qualify.

[bernse]

While not as often as the US, we get them in Canada (especially the Prairie provinces) with some frequency.

[dqa]

To answer Wumpus, the Fujita-Pearson scale is as follows

F-0: 40-72 mph, chimney damage, tree branches broken
F-1: 73-112 mph, mobile homes pushed off foundation or overturned
F-2: 113-157 mph, considerable damage, mobile homes demolished, trees uprooted
F-3: 158-205 mph, roofs and walls torn down, trains overturned, cars thrown
F-4: 207-260 mph, well-constructed walls leveled
F-5: 261-318 mph, homes lifted off foundation and carried considerable distances, autos thrown as far as 100 meters

Source: FEMA

[Niobium Knight]

how frequent are F-5s then?

[BobT]

According to this link
http://www.spc.noaa.gov/archive/tornadoes/f5torns.htm

There have been 52 (or thereabouts I counted quickly) F-5 tornadoes recorded in the U.S. since 1950.

There were 7 of them on April 3, 1974.

[panamajack]

NOAA has a lot of excellent info on the Tornado Outbreak of April 3, 1974 (which happens to also be the day I was born).

The only area outside the US that receives a lot of serious tornado activity is Bangladesh (and nearby parts of India). There it is often more of a mix with monsoons and thus a bit harder to compare directly on a scale with American tornadoes.

Severe weather is more deadly there, since housing is often even worse than trailer parks and associated flooding spreads disease after the storm. The most severe events have resulted in over 1000 deaths (by comparison, the April 3 in the US incident resulted in over 300 deaths).

[lesa]

This is the way I heard it explained on The Weather Channel.

The jet stream blows across the US from west to east. At certain times, warm wind from the Gulf of Mexico blows to the north west. The air meets and begins to swirl. The warm gulf air reacts with the relatively cool jet stream, causing strong storms and tornadoes.

So this part of the US is prone to strong tornados because of geography.

[Cerowyn]

Originally posted by panamajack
The only area outside the US that receives a lot of serious tornado activity is Bangladesh (and nearby parts of India).

Three or four seconds with Google suggest that this is not accurate. For instance, Environment Canada says:

In Canada, during an average year, 80 tornadoes cause two deaths and 20 injuries, plus tens of millions of dollars in property damage. These are the reported numbers - who knows how many more tornadoes strike unpopulated areas undetected.

[panamajack]

I wasn't saying there aren't tornadoes anywhere else -- I said "serious tornado activity". Relative to the central U.S. (upwards of 20/ 10,000 km²/yr) or Bangladesh (unknown, possibly in the tens), Canada isn't very high up there (a small part of Ontario has 2/ 10,000 km²/yr.).

But my computer crashed as I checked my last cite, so I'll just amend my statement to "North America".