In order to determine weather events, Environment Canada will conduct a damage survey. Based on the look and direction of damage, they're able to conclude the type of severe weather generated.
Often times, investigators will deduce the damage to either tornadic activity or straight-line winds. But what is the difference between the two? Geoff Coulson, Warning Preparedness Meteorologist with Environment Canada explains.
Straight-line winds and downbursts
“When we're talking about a downburst or a straight-line wind event it is literally a localized powerful gust of wind that comes out of the base of the thunderstorm,” notes Coulson.
Speed also plays a role in storm intensity and subsequent damage.
“If the thunderstorm is slow moving it can produce almost a starburst pattern of damage as the winds hit the ground and spread out in all directions.”
If the storms are moving relatively quickly they tend to have the biggest effect at the leading edge of the storm. “This is because the speed of motion of the storm adds to the wind gusts coming out of it.”
It's this leading edge that tends to produce the most severe damage. This was was the case in the Coboconk, Ontario area on Wednesday.
Microburst and macroburst
Dayna Vettese, a meteorologist with The Weather Network says a microburst is essentially the same as a downburst with only a slight variation.
“The main difference is that a microburst creates less than 4 km of damage and contains peak winds that last 2 to 5 minutes.”
Vettese says a macroburst has a bigger radius of damage whereas a microburst is smaller but usually more intense due to a higher concentration.
Coulson defines a tornado as a violently rotating column of air in contact with the surface.
“As opposed to straight-line winds, twisters tend to produce damage in a more narrow and long damaged path.”
This occurs because tornadoes themselves may only be a few tens of metres wide and “...they're drawing in all that dirt and debris in towards the centre of the tornado path.”
The Fujita or F-Scale measures wind and its damage. The scale is divided into six categories with F0 being the weakest and F5 being the strongest.
However, the Fujita Scale isn't just used to measure tornado intensity. Coulson says it's also employed to determine the strength of straight-line winds.
“The Fujita Scale looks at the type of damage caused to produce that kind of damage -- whether the winds were actually rotating violently in a tornado or blasting out of the base of the thunderstorm.”
He says the scale can be used to determine or at least estimate those winds in both cases.