Tornado Formation (Do tornadoes only occur in North America?)

In the recent Straight Dope Classic #3, Do tornadoes only occur in North America? (Jan 10 2014, originally Aug 6 1993,

Cecil reports that tornadoes common form in the US because “you get warm, moist surface winds blowing up from the Gulf of Mexico, while cool high-altitude winds blow over the tops of the Rockies.”

This is not right. Tornadoes form so commonly in the US and Canada because there is one long plain that extends from the Arctic Ocean to the Gulf of Mexico without any geographical features to block the air masses from the Arctic from meeting those from the Gulf.

The Rockies actually block the winds from either direction, preventing the air from extending westward, they do not generate the cold air. This can be seen in a map of tornado locations, which sweep at a NW-SE diagonal that tracks the front of the mountain range. This is also one of the reasons that tornadoes do not form west of the Rockies - where there is warm air from the Pacific currents that give the west coast such a pleasant climate compared to the east coast at identical latitudes.

So the cold Arctic air sweeps across the lake-littered glacial tundra of Canada’s Northwest Territories into Canada’s Great Plains of Saskatchewan, Manitoba. northern Ontario and eastern Alberta, and onward to the US Great Plains where they meet the Gulf air coming north.

The many lakes of the tundra and plains of Canada and the northern US are also remnants of the glaciers. You will see a similar pattern between lake location and tornado formation because the Rockies blocked the glaciers as well. And the existence of this vast low-lying plain explains the childhood mystery of why there are fossils of fish and other marine life in Kansas.

An additional consequence was the formation of one of the world’s few high latitude desert regions in the Great Basin between the Rockies and the various mountain ranges that cross the region to the Pacific coastal chains (the other being the Taklamakan-Gobi Desert system where various mountain ranges and plateaus enclose the region in an east-west manner).

Antarctica is the only continent that hasn’t had one.

I believe the country with the most tornadoes per land-area is the Netherlands, folowed closely by the U.K. Of course, the U.S. is a lot bigger and individual states (Nebraska, Kansas, Oklahoma, Texas) come in a lot higher on the list.

Antarctica is the only continent where no tornadoes have been observed. Absence of evidence is not evidence of absence, especially when there have been very few observers who have been very restricted in terms of location and timespan.

The first confirmed landing of a person on the continent was in 1895. The first permanent habitation on the continent was the Bernardo O’Higgins station founded by Chile in 1948. Currently, the population of Antarctica and surrounding islands ranges from 1000 in winter to 5000 in summer - and many of those are clustered on the Antarctic Peninsula and nearby islands.

So there is very little data about Antarctic weather, and it is all very recent. There are many places in the world where certain weather phenomena are very rare and infrequent but do occur every few centuries or millennia.

No one knows if there are tornadoes in Antarctica.

This NOAA page gives the basic information about tornadoes. Looks like they don’t know why they form. May I please wager on both the OP and The Master being correct?

Minor nit-pick

There have been tornadoes recorded in all 50 states since 1950. Some form west of the Rockies. (Unless they’re just really far east of them) :wink:

Many hurricanes (also called typhoons and cyclones) spin off multiple tornadoes, as part of their remarkable assortment of destruction.

Where does the warm moist air come from for “Moscow, and Vienna” ? I can envisage hot wet air heading north from the Bay of Bengal to get to Peshawar (though with it being close to the Himalayas it’s not exactly in the same sort of “Canada / US Great Plains” corridor that we associate with North America’s tornadoes"

An interesting tale from our local area here in the western USA. We had a regular thunderstorm (as opposed to a severe thunderstorm) moving north being shielded from a strong westerly wind by a mountain ridge. As the t’storm moved into a gap in the ridge, you could watch in the radar images how the northern part of the storm got sheared off and spun off as a tornado. This tornado peaked at EF2 even though it spun out with retrograde, or clockwise motion.

I seem to remember the NWS stating this was a “once in a thousand years” event, or 0.1% odds. There’s many many ways to bring about the right atmospheric conditions, where even a slight twisting motion will ramp up to a tornado. What The Master presents is the most common, but the OP’s ideas are just as valid, just not as common.

Tornado formation

Cecil did not state that the Rockies generate cold air. Rather, the cold arctic air typically is directed by the Jet Stream, which flows down from Canada across the Rockies. This dumps moisture onto the Rockies in the form of snow and leaves the air that goes over the Rockies cold but relatively dry. There it meets air flowing north from the gulf, wet and warm. That is what creates the wind shear to form mesocyclones. Though cold air does flow down further east, and is why tornadoes form in areas distant from the Rockies.

Yes, those regions of Canada are also highly tornado prone.

That NOAA page is misleading. There are a lot of details of tornado formation that are not known and a lot of active research into the specifics, but some general formation information is known, such as the role of mesocyclones in forming powerful tornadoes.

See ongoing research.

OK, you got me. I chuckled when I pulled up that picture.

Note also that the formation is likely not in North America, but in Western Europe. :wink:

Tornadoes occur on the SUN, ever see a video of one, they are thousands of miles high.