A farm outbuilding destroyed by the downburst in Thedford. (Photo courtesy of the Northern Tornadoes Project)A farm outbuilding destroyed by the downburst in Thedford. (Photo courtesy of the Northern Tornadoes Project)
Sarnia

EF1 downburst reported in Thedford

Environment Canada agrees with findings from the Northern Tornadoes Project (NTP) that a downburst, not a tornado, caused the damage in Thedford seen last week.

Tornado watches and warnings were issued for Lambton County on July 20 as a line of severe thunderstorms swept across southwestern Ontario.

A NTP team surveyed storm damage on July 21 in areas including Thedford and Wyoming.

It was determined that damage south of Thedford was caused by an EF1 downburst "in the rear-flank downdraft area of a supercell thunderstorm."

The downburst had an estimated maximum wind speed of 150 kilometres per hour. The downburst also occurred during the same time a funnel cloud was observed north of the damaged area.

According to the report, there was "weak damage" in multiple locations that spanned at least 6.5 km long and 3.8 km wide.

"The way the damage looks from a downburst event, if the storm is moving relatively quickly, the damage tends to be pushed in the direction the storm is moving and the width of damage tends to be relatively broad," said Environment Canada Warning Preparedness Meteorologist Geoff Coulson. "Whereas with a tornado, the winds tend to be very violent but very narrow and concentrated and so the damage track tends to be more long and narrow."

Coulson said he's not aware of any other downbursts or tornadic events that occurred in Lambton County last week.

There was structural and tree damage but luckily, no injuries were reported.

The summer severe storm season in southwestern Ontario tends to span from late April until early October, so Coulson said there's still potential to see more active weather.

At least for a few days, no watches or warnings are anticipated.

"Our next chance of any real active weather would be Wednesday when we could see some showers and maybe even a few thunderstorms kicking off in the area," said Coulson. "As we finish off the work week and head into the weekend, again [it's] back into a more seasonal trend for temperatures and a somewhat quieter weather pattern."

Coulson said precipitation in the region will likely come in short bursts and not the gentle, long-lived rain farmers are hoping for.

A heat warning issued for Sarnia-Lambton on July 18 ended early Monday morning.

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