ONTARIO: Thunderstorm Forecast for Monday, June 26, 2023
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FORECAST DISCUSSION
Thunderstorms from the previous evening's severe weather in parts of Southern Ontario are continuing to move across the region overnight. These storms are expected to be non-severe but could bring heavy rain and strong wind gusts. In Eastern Ontario, this activity will persist into the pre-dawn hours.
The timing of these morning storms will play a crucial role in determining the overall risk for later on Monday. Current models indicate that they will clear out by noon, allowing the atmosphere enough time to recover and support the development of severe storms in the afternoon.
Our concern is growing for the Ottawa Valley, particularly in the early afternoon. Models suggest that isolated storms may initiate as early as 2 PM, extending from Brockville through Ottawa and into Algonquin Park. If this occurs, the environment would be favorable for rapid intensification, with the potential for large hail up to the size of a tennis ball or golf ball, wind gusts of 100 km/h, and heavy rainfall. Additionally, one or two tornadoes may be possible.
Later in the afternoon, a line of storms is expected to form as isolated storms over Upstate New York move across Lake Ontario. This line will rapidly bow out as it progresses northward, starting with the Kingston region. The main threat with this line will be widespread damaging wind gusts exceeding 100 km/h, based on the anticipated storm pattern. Although the possibility of a tornado cannot be completely ruled out, the risk is uncertain.
There are also indications of a strong flood risk through the Ottawa Valley including the city with models showing 100+mm of rain in a 6-12 timeframe. For the rest of Southern Ontario, including the southwest and Golden Horseshoe region, we anticipate isolated pop-up storms during Monday afternoon and evening. Currently, it appears that these storms should remain non-severe, but we may need to expand the isolated risk zone in the morning as we gather more information.
