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Why are tornadoes more severe in the US than any other country?? I have always asked myself this question. Maybe geography plays an important role. If that's the case, then why doesn't Canada or Australia receive the same amount of tornadoes?? They all have similar geographies and climates.
Last edited by nature's message; 04-26-2009 at 08:47 AM..
Reason: Wanted to change question
Maybe the question should be why are tornados on average more SEVERE than other countries. On a per square mile basis it does NOT get more tornadoes than other countries, but they are more severe.
As to why they tend to be more SEVERE, it is really because the continent spans such a range of latitudes, whereby solar radiation received varies a lot, temperatures in different areas of the continent are very contrasted particularly during spring and autumn, some areas are very dry such as the west whereas the south and east is relatively humid, and obivously cool continental air in the north. This gives many opportunities for great instability over the continent, particularly its mid-section, especially when the jet stream moves north in the spring. The jet stream is a passage of very fast moving air seperating polar continental air in this case from the humid subtropical air, and which drives low pressure areas that form; these develop fronts (boundaries) between the aforementioned air masses, that in combination with the great instability in the atmosphere results in the initial thunderstorms, while the variation in upper level wind direction and increase in its speed with altitude provides the rotation mechanism for the updraft which allows tornadoes to develop.
As to the question about torndoes in the US, well as for why there are so MANY, it is simply because it is a large country, and a well populated country, so more tornadoes are noticed. Who's to say parts of Asia and Australia don't have similar numbers of tornados for a given land area? They have far less population density, so their tornadoes are more likely to go unnoticed.
England statistically has more tornados per 10,000sq km than any other nation!
Even my county of Lincolnshire (2,700sq/miles) has had a number of weak tornadoes in 5 years that is equivalent to the tornado density per square mile of Oklahoma. Three of which were within 10 miles of my home (29th september 2006, 13th + 15th June 2007) and one which was an F2 tornado (May 2006).
Oklahoma, most tornado prone state in the US, averages 8 tornados per 1000 square miles per annum. Well, Lincolnshire, UK averages a similar number! Then, consider the average of the whole of the US is less than that. Here is a list of some of those known between 2005-2007 (less than 2 years).
28th July 2005, Moulton - the same day as other violent tornadoes destroyed property and caused serious injuries in Birmingham & Peterborough
http://www.youtube.com/watch?v=AuEWKip44B4
That vid shows a tornado that started in birmingham on the same date, a very stormy day that was. The video is poor quality but it became an F2 tornado.
20th April 2006, Ingham
16th May 2006, Sleaford
17th August 2006, Baston
29th September 2006, Belchford (I remember this awesome thunderstorm!!!)
13th June 2007, Ingham
15th June 2007, Belchford (Remember that too!)
That is all I can find right now, but even those tornadoes would give the area a rate of about 3-4 tornadoes a year per unit area, greater than the entire western half of the US, but not as great as the USA midwest. That's just in ONE county of England.
Canada doesn't have similar climactic conditions for what causes tornados in the U.S.A.
A solid 1/3rd of the Lower 48's landarea is predominantly "subtropical,"
and most of this land area is west of the Rockies, where the land is mostly flat and open to Artic/Canadian airmasses.
Anywhere as far north as Oklahoma and Tennessee is more influenced by the Gulf of Mexico than any other geographic influence.
So when you combine relatively warm/hot and humid condions
with few natural barriers to invading polar air,
it's a recipe for easy tornado production.
** Even in Canada, most of our fuel for tornados comes from air masses originating from the Gulf of Mexico...
the difference is that due to our distance, we are rarely influenced by winds from the Gulf.
Ex: 1/10th of the year in Toronto vs. 2/3rd's of the year in Tennessee.
Canada has the severe cold to trigger severe storms, but we don't have any areas that on their own, generate a lot of muggy warmth.
A solid 1/3rd of the Lower 48's landarea is predominantly "subtropical,"
and most of this land area is west of the Rockies, where the land is mostly flat and open to Artic/Canadian airmasses..
Umm no offense bud but I think your facts are wrong. West of the rockies? Its actually east of the rockies. And 1/3 of the U.S. is not subtropical.
The reason that the U.S. has more tornadoes is because the center part of America is mostly flat EAST of the rockies all the way to the Applachians.
Just think of it this way. The center of the North American Continent is flat. So basically cold air (which is dense and shallow) can pour south. Essentially warm air from the gulf of mexico can move north, and in basic simple terms where the cold air mass collides with the warm air mass from the south you get active weather like thunderstorms, and tornadoes and heavy rain.
The gulf coast and southern atlantic provides the fuel for tornadoes.
Umm no offense bud but I think your facts are wrong. West of the rockies? Its actually east of the rockies. And 1/3 of the U.S. is not subtropical.
The reason that the U.S. has more tornadoes is because the center part of America is mostly flat EAST of the rockies all the way to the Applachians.
Just think of it this way. The center of the North American Continent is flat. So basically cold air (which is dense and shallow) can pour south. Essentially warm air from the gulf of mexico can move north, and in basic simple terms where the cold air mass collides with the warm air mass from the south you get active weather like thunderstorms, and tornadoes and heavy rain.
The gulf coast and southern atlantic provides the fuel for tornadoes.
That was a typo.
*I KNOW all that, already... and that was exactly what I was thinking.
Sub-tropical by world standards? Maybe not.
Subtropical by American standards? Yes.
Try to find a climate map of North America and you'll find anywhere in eastern North America where the coldest average highs are still above 45 F will be rated "subtropical."
It is not meant to intend that palm trees will grow easily,
but a cilmate that is mild enough snow is "not normal" even in winter AND has "long, hot summers."
(which is why the Pacific NW doesn't fit in )
Last edited by ColdCanadian; 04-29-2009 at 04:12 PM..
Another important element in the production of tornadic storms is the supply of hot, dry air from the southwest. One of the reasons why the southern Plains are so vulnerable to violent tornadoes.
BTW, Florida is almost as tornado prone as the southern Plains, largely due to the large number of thunderstorms it receives. Florida is not nearly as vulnerable to violent tornadoes, however. It is during the winter months - when cold air masses can invade from the north - when Florida can occasionally experience severe (F3) tornadoes. Violent ( F4 +) tornadoes are very rare in Florida.
There are a number of 'Tornado Alleys', not just the one centered on OK/KS/TX. One of the most notorious is in northern Alabama, along the Tennessee Valley. Others include the Ohio Valley and around major river confluences such as the Mississippi/Missouri around St Louis and the Missouri/Kansas around Kansas City. Suggesting that river valleys and urban 'heat islands' may have an effect in 'pepping up' thunderstorms.
Sub-tropical by world standards? Maybe not.
Subtropical by American standards? Yes.
Try to find a climate map of North America and you'll find anywhere in eastern North America where the coldest average highs are still above 45 F will be rated "subtropical."
It is not meant to intend that palm trees will grow easily,
but a cilmate that is mild enough snow is "not normal" even in winter AND has "long, hot summers."
(which is why the Pacific NW doesn't fit in )
According to Wikipedia, even NYC is subtropical due to January average being 32 F (0 C), mainly due to heat island effect. Doesn't quite feel subtropical if you ask me, but hey I'm not climatologist.
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