ONTARIO: Thunderstorm Forecast for Thursday, July 20, 2023
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FORECAST DISCUSSION
A line of significant storms has developed over Central Michigan this afternoon and is currently tracking toward Southern Ontario. Based on the environment, we have upgraded our forecast to an ‘extreme’ severe risk for Deep Southwestern Ontario. This is our highest threat level and is reserved for events we believe are going to be widespread, destructive, and pose a significant risk to those in the storm's path.
Generally, this level is used in the case of tornado outbreaks or destructive wind events, which, in today's case, is the latter. While the tornado risk is present, it likely won't reach outbreak status - although that can't be ruled out completely.
The main concern will be an intense line of storms sweeping across Southwestern Ontario during the late afternoon and early evening hours, bringing widespread wind damage stretching from Georgian Bay and southward into Windsor. Additionally, localized pockets of extremely large hail up to tennis ball-sized (that isn't a typo!) are also likely today with these storms.
This line will continue into the Golden Horseshoe and Central Ontario, where the wind damage threat will be quite strong through the evening hours. Thunderstorms will reach Eastern Ontario somewhere around midnight and could bring isolated damaging wind gusts, with the tornado threat becoming less of a concern later in the night.
TIMING of the strongest risk
Southwestern Ontario: 3 - 7 PM
Central Ontario: 4 - 9 PM
Golden Horseshoe: 6 - 10 PM
Eastern Ontario: 10 - 2 AM
TORNADO RISK
The tornado risk for this event is strongest in Southwestern Ontario, from Windsor and up to the Eastern Lake Huron shoreline. This is where we expect to see at least a couple of tornadoes, with a strong long-tracked tornado not out of the question. These tornadoes may spin up quickly without warning and could be rain-wrapped, making them hard to see coming.
One or two tornadoes are possible to the east from the Niagara region and up into Central Ontario. This is mainly for the potential of isolated storms popping up ahead of the main line around Georgian Bay and Lake Simcoe later this afternoon. The tornado threat will diminish later tonight by the time the main line of storms moves through, so we will likely have just an isolated tornado threat with that.
We can’t emphasize enough how serious and dangerous it could get this afternoon into the evening across Southern Ontario. You NEED to ensure you stay aware of the weather today and have a plan in place to seek shelter if severe weather approaches. This will be a very widespread event, so almost everyone will likely see some form of severe weather today. Please stay safe!
