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Tornado or downburst, what’s the difference?

Tornado or downburst, what’s the difference?

As news spread yesterday morning about Toronto's Don Valley Parkway being flooded out it was wind, not water, causing problems on the city's west-side, as Brampton residents reported damaged trees, signs and roofs, and even a warehouse having one wall completely blown out.

As southern Ontario has already seen two tornadoes so far this year, if thoughts immediately turned to another twister as the culprit, it would have been completely understandable. However, after a team from Environment Canada checked out the damage, they found that it likely wasn't a tornado, but something else called a 'downburst'.

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Downbursts happen when a strong thunderstorm that's making a lot of hail and/or large raindrops moves over an area of dry air. The dry air won't let the hail or rain just fall through it, though. It has to soak up that moisture for awhile before it will let any get to the ground, and melting the hail and evaporating the water sucks up a lot of heat in the process. That chills the air down and makes it very dense, very quickly, and that air plummets towards the ground at speeds of up to 150 km/h!

The major difference between what we see on the ground from a downburst and a tornado is that the winds from a tornado suck things inward and the winds from a downburst push outwards. Usually, from a tornado, you'll see the damage whipped around in a spiral, but the damage from a downburst is typically lined up all in the same direction. You may have also heard of a 'microburst'; that's just a downburst that only effects a very small area (and are a particular concern to pilots).

Also, whereas tornadoes can last for quite a while — the longest recorded left a damage path 350 kms long over three and a half hours — downbursts only last for a few minutes, tops.

In the case of the damage done yesterday morning, the investigation team figured out that the winds were traveling at between 90 and 100 km/h (compared to 10-20 km/h at Pearson Airport, about 10 kms away), and their report said that most of the damage lined up towards the east, which is the direction the storm was traveling at the time.

Although they're certainly not an every-day occurrence, downbursts are definitely more common than tornadoes in Canada, and they can sometimes do just as much damage as one, too.

On April 23, 2007, a powerful storm passed through Vaughn, Ontario, northwest of Toronto. Downbursts from the storm tore apart a warehouse that was under construction, snapped a telephone pole, blew an air-conditioning unit off the top of a building, and even flipped a huge steel shipping container up a small hill.

On July 27th, 2010, at around 2:30 p.m., a storm that produced "hail, torrential rain and heavy winds" passed through Hensall, Ontario, near the southeast shores of Lake Huron. The storm kicked off a downburst with wind speeds up to 90 km/h, that snapped tree limbs and knocked out power to the village for the rest of the day.

June 2011 were a busy month for downbursts, as one with winds of around 90 km/h downed trees and powerlines in Hamilton, Ontario on June 8th, and another with winds measuring up to 110 km/h ripped trees from the ground in the Leamington and Kingsville on the afternoon of June 21st.

As this video shows, from June 21st, 2012, taken in London, Ontario, the winds can be very powerful and the entire event can pass very quickly:

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Even though Canada generally has a lower risk of tornadoes compared to the United States, meteorologists recommend that Canadians should still prepare for the possibility of a tornado when heavy thunderstorms are in the area. The best thing to do is keep updated on weather warnings from Environment Canada, but people are advised to have a disaster plan in place, including supplies of food, water, batteries, cash, medications and a radio, and knowing where the best place to take shelter is in your home. During a tornado, the basement is typically the best place to go, but if that's not possible, a small interior room on the ground floor, with no windows, such as a bathroom or closet, is the best alternative.

More scattered rain and thunderstorms are expected in southern Ontario today, Friday and Saturday, but it looks like the weather is going to calm down some going into next week.

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