My partner and I were trying to find video or pictures of Australian tornados and started discussing why America seems to get a lot more than we do.

So I have two questions. Can tornados only form in supercells? And why don't we get as many as America?

No, tornadoes can also be formed from other types of storms.



Loaded question, probably would need several pages of text to adequately answer that question. Short answer, no Gulf of Mexico and no Rocky Mountains. The Gulf of Mexico is a rich source of moisture. The Rocky Mountains provide an "elevated mixed layer" which inhibits convection till everythings primed.

tornadoes need warm moist air clashing with cool dry air they also need turning windshear to make the storm rotate for supercells they need heating from the day aswell

they are many tornadoes that go unreported in Austrailia most tornoadoes form from supercells but there are a few that dont like the ones that form in Wa during the winter cold fronts

why does USA get more tornadoes well they get a heack of alot more energy than we do here which makes for more supercells

that is my very brief take on it

Victoria is also known for the occasional winter tornado from what I believe is referred to as "cold core" thunderstorms...something I haven't really studied. Supercells are obviously the best tornado producers though, for the simple fact that for a storm to be classed as a supercell it needs to contain a Mesocyclone (a persistent rotating updraft). And of course, once a storm starts rotating, their is a chance that rotation will lead to a tornado.

Tornado Alley in the US is a unique location. During the Spring months there is regular collisions of cool dry air and warm moist air leading to severe weather, as Squid mentioned. Add in a powerful jet stream and miles and miles of flat land and you have a recipe for Supercells and Tornadoes.

Here's a good article with a nice diagram - http://www.nssl.noaa.gov/primer/tornado/tor_climatology.html

Also Australia never seems to get the awesome deep layer/low level wind shear the US gets which definitely would have to play a big part!

Thanks for the answers so far guys. Meso that link was great, thanks heaps.

As others have correctly mentioned no Gulf of Mexico, however this would be a rather latent energy source if it were not for the continental mass stretching far to the north.

Another factor in Australia we have DO NOT get a fraction of the mid latitude continental low pressure systems that the USA enjoys. This is a direct consequence of our cool oceans to the south and east. In the US the continental lows boost or provide jet streams, but also suck that Gulf of Mexico moisture northwards. I have seen situations where cool dry air has been replaced by humid warm across near all the plains in around 24 hours. These are often in the form of a warm front...how many of those do you see on an aussie map?

December 2004 in NSW/VIC comes close to a typical US setup, but these are a rare setup here.

I believe both parts of South America and South Africa have strong tornadoes from time to time. I would think the frequency of warm season mesocyclonic tornadoes in both places is greater than in Australia. Take this recent tornado in South Africa for example-

http://www.youtube.com/watch?v=18YxQ4YYAkY

I tend to think that Australia is a bit messed up for big storm outbreaks. Personally, I would like to see Australia shifted a bit further south. This would put a great land mass in the mid latitudes (where strong vertical wind shear and CAPE are more likely to co-exist) and also open up more tropical waters to our north (greater moisture for mid-latitude systems to tap into). The Great dividing range annoys me so it will be shifted about a 1500 km inland. The elevated terrain in Western Australia, South Australia and Northern Territory will provide a strong elevated mixed layer that will cap a moist boundary layer over Qld, NSW and Vic leading to the formation of a near permanant dryline in spring/summer. When short wave troughs eject over the great plains of Qld, NSW and Vic, cyclogenesis shall occur and Australia will be a storm chasing nirvana.

Lol. If only we could play god like that.

I think the Australian continent separated from Antarctica about 40 million years ago and has been drifting North ever since (and is still doing so at about 5cm per annum). So Australia might have been better for storm chasing about 10 million years ago.

As for the Great Dividing Range - we could get a few shovels and a few wheelbarrows and get cracking.

From my casual observation of Australian weather (from NZ) I think the lack of a low level jet is the reason for a lack of tornadoes in Australia. There is plenty of spring and summer instability but it tends to come with shallow surface troughs. As Michael suggested in his post, the Great Plains of USA get deep surface lows and these lead to strong low level southerly flows which result in large helicity values.

I fully agree with you regarding the lack of a low-level jet. Though I guess the real question is what leads to the development of a strong low-level jet over the great plains. My undestanding is that the Rocky Mountains play a major role.

Low-level jets-
http://www.ge-at.iastate.edu/chen/printversion-31.pdf

Lee side cyclogenesis-
www.theweatherprediction.com/habyhints/129/

Problem with Australia is we get too many troughs whereas the states get LOWS which then cause other changes such as the LLJ and increases in helicity.

TS

Genuine question here TS, does that mean that the USA dosent get the "double-yolker" simultaneous weak highs that we often get over our southern mainland during our warm season? Meaning our trough lines normally ocurr at the "interseam" of these?

I was going to ask if not/why - but (possibly) the obvious reason might be the fact that we are separated from the Antarctic ice fields by water versus land for the USA continent? Not that I have the brains to understand the permutations of this difference .

unless the so called polar shift happens next year.

Not sure if it was fully covered by previous posts but the ideal Tornado setup needs Cold-Dry air in the upper layers and Warm-moist air in the lower layers. For this to happen you need warm ocean temps to help create the warm humid low layers and a cold front to provide the cold. However it is never easy to get the cold dry air to move over the warm moist. In the Mid-West of the USA the warm moist air is supplied from the very warm Gulf of Mexico waters. The cold dry air above moves over the Rocky Mountains with the Mountains acting as a barrier so it does not just undercut the warm moist air, but rather has a chance to move over the top of the warm moist air east of the Rockies. This is a very unique geographic combination in the world which is why places like Oklahoma and Kansas have by far the most tornados.

Tornadoes can form briefly from large thunderstorms as in Australia but these are not really in the same league as the US tornados.

This is far from being the truth, and a common misconception.

In fact the geographic conditions arise elsewhere, in fact where large mountain ranges coincide with the tropical airmass is in more locations that you might guess. Just for a few examples: Lee of the Andes around Argentina level, tropical moisture comes off the Amazonian rainforest, with the high terrain providing the steep lapse rates and EML needed. Or how about Bangladesh, where the juxtaposition of steep lapse rates, a strong capping layer (the presence of elevated terrain which when heated produces a layer which traps the moisture near surface), incredible moisture values can produce CAPEs into the extraordinary levels of 9-10,000, which when combined with maybe 40 knots of shear have produced tornadoes which kill hundreds. Other locations include: Europe, particularly NW Italy, but pretty much anywhere the steep lapse rates from the elevation intersect air from the Med (mostly balkan states downstream, occasionally Germany/Fr), South Africa (resulting from the highveldt, though severe storms are quite rare in that part of the world), China (moisture from the east intersects the tibetian plateau air. I could go on but there are plenty of other limited geographical examples. The US is probably the best combination of air mass collison, but others are have similar effects with slightly lower frequencies.

In Australia we get the supercells, but all too often shear is too weak to keep the environment discrete, or the capping insufficient to prevent a mess developing (more commonly seen the further north you go) . In fact, by interesting coincidence, the deserts of NW Aus can produce a reasonable EML but unfortunately its nowhere near as deep as having 2000m plus terrain to get the surface heating. We do have a lovely moisture source as well, in terms of the coral sea and the Gulf of Carpentaria. The problem is the cyclogenesis conditions required to increase Helicity, and produce a low-level jet are fairly uncommon. With high terrain comes the prospect of lee-cyclogenesis as mentioned above, in the states its a common occurence in the lee of the Rockies, and the same is true for each of the others listed above (South Africa has the same problem as us, there isn't enough land mass east of the continental mountain range to allow that lee effect to be over land).

So what about the shear? Well the deep layer shear magnitudes seen over the Australian continent are generally of similar magnitude. Shocking right? Well actually the main difference is a decrease in frequency, as the conditions to set up the type of events don't occur as commonly, but our season tends to last a bit longer than in the states. If you look at the 0-1km shear however, in Australia its pretty paltry. Without the LLJ you just don't see the 30-60 knots that is commonly seen in the major tornado outbreaks (for instance the April 27th event this year, 90 knots of shear, 60 knots of that 0-1km). However, we do actually get cyclogenesis events in Australia! When these occur we generally see tornadoes and significant tornadoes. For instance: March 6/7 2010 saw the conditions line up, shear was ridiculous and the storms were as well, a number of tornado paths were observed. The Bucca Tornado was also associated with another cyclogenesis event in 1992, and was violent, most likely an F5 had it hit anything more significant...again there were other tornadoes on this day. There was even a recent event in November in Victoria and Sth NSW that saw a cyclogenesis event spawn environments with 70 knots of shear, and had things lined up 0-1km SRH in excess of 400 m^2/s^2 (To give an indication, the Joplin EF5 tornado formed in similar numbers)...only one storm really formed in this, preventing the risk. I could go much further with the listing but the summary is they do happen.

Truth of the matter is, Tornadoes can form anywhere that a supercell thunderstorm can. Which pretty much means any continent (except Antartica)! Sure the states has the greatest frequency (probably around 2500 per year), probably followed by South America, Bangladesh, Australia, Europe etc. Europe doesn't get enough CAPE most of the time, with aus having a greater frequency of CAPE >2000 J/kg.

Anyway, happy to provide more facts, but you need to remember about 1 in 100 tornadoes is F3 strength or great, with only ~1 in 1000 being F5 strength. So if like Australia your annual occurence is probably only 100....an F4/F5 tornado would occur every 6-10 years, which is pretty much how often we see them (Note this is contingent on strong tornadoes hitting populated areas with structures capable of withstanding winds to give a damage pattern). There is no difference in league, only our population being 85% coastal means the exposure is limited to cause damage.

Severely Tall, can you give me one example of Tornado footage, or pictures of a Tornado path that is anything above an F2 from Australia. The best I have seen from Australia are brief erratic touch downs of F1 or F2, I certainly have never seen anything remotely like a proper Tornado from Australia.
Yes brief Tornados do occur anywhere but Antarctica but I have never heard of an F5 from anywhere but the USA.
Take a closer look at that geographic setup in the USA, The Gulf waters are among the warmest in the world, as warm as off Broome WA. You need large expanses of flat plains like mid-west USA for F5 formation. Then you need that cold dry air aloft, the Rocky Mountains are not a narrow range but a vast area of high country in longitude that is land connected to the North, this makes its an ideal source of cold dry air aloft with prevailing upper westerlies.
Although some parts of the world have hints of this set up, SW Brazil, NE China, its still no where near the perfect geographic set up as in the USA.
I am sure you have a good understanding of the physics for Tornado formation and the numbers may suggest it could happen elsewhere, but observations speak for themselves, I do not think its just population or lack of observations from elsewhere.

Excellent post Severely Tall. I think I have made a similiar point before, in Australia 0-6 km shear values of > 40 knots with moderate-high CAPE are not particularly uncommon therefore we receive our fair share of supercells with very large hail. It's when we start looking a low-level shear where many Australian storm setups fall short. Though SA, Vic and western NSW often have excellent setups with strong shear with nicely curved hodographs but then LCL's are usually very high and a limiting factor for tornadogenesis.

PeterDuke,

The Bucca tornado, 29 November 1992- rated F4, look at these photos, it's obviously a very strong tornado - http://www.bsch.au.com/photos/display.html?id=subs/291192_01

The Bulahdelah Tornado, 1 January 1970- 22km long and 1-1.6 km wide. I have a copy of the BoM report so I can confidently say this is not an urban myth