Strong Severe Risk With Tornadoes Possible on Monday in Eastern Ontario Including Ottawa & Kingston
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The severe weather season is certainly off to a busy start across Southern Ontario as we enter the final week of May. Just last week, we had our first 'strong' severe weather risk of the season, and this week, we're facing our second strong severe weather threat for Monday afternoon.
While last week's risk predominantly affected Central and Southwestern Ontario, the strongest risk for Monday will shift to Eastern Ontario, including the Ottawa Valley. Multiple rounds of storms starting late Monday morning and continuing throughout the afternoon could bring damaging wind gusts and large hail. A few tornadoes are also possible, with the environment potentially being the strongest we've seen this season.
Further to the south and west, there's an expansive risk for marginally severe storms during the morning and early afternoon hours. This is mainly due to the flooding threat, as models indicate multiple rounds of storms could impact the Golden Horseshoe region into Central Ontario. Some areas may approach 75 to 100mm of rain, with the bulk of that coming in just a few hours. Nickel-sized hail and 90km/h wind gusts are also possible.
As of Sunday night, a decaying line of non-severe thunderstorms is tracking across Southern Ontario and is expected to continue into Central and Eastern Ontario during the predawn hours. Just after sunrise on Monday, another cluster of storms is expected to cross over Lake Erie and track toward the Golden Horseshoe.
These storms should be predominantly non-severe, especially given the early morning timing. However, some models indicate an environment building toward the late morning hours that may support storm intensification to marginally severe levels.
This includes the Greater Toronto Area and Central Ontario around Lake Simcoe. Again, flooding would be the main concern, especially with the heaviest rain potentially targeting the urban core of the GTA. The tornado risk should be fairly low at this point in the day, with the main focus being hail and strong wind gusts.
This same complex of storms will track into Eastern Ontario by the early afternoon. The arrival of this line will be critical. If it arrives too early, it could wipe out the environment needed for severe storms for the day. But if it arrives much earlier, like during the morning hours and clears out before noon, the environment will have lots of time to recover with more isolated storms later in the day.
Currently, the consensus is this line arriving around 1-3 PM with additional storms forming ahead of the main line. The actual line may also further intensify as it approaches Eastern Ontario, with potentially destructive winds developing from Kingston to Ottawa and tracking to the northeast.
If we get isolated storm development ahead of the line, they could pose all types of severe hazards, including large hail up to the size of toonies or even ping-pong balls, damaging wind gusts, and potentially tornadoes.
The tornado threat is highest with the isolated storms, but we could also see some embedded rotation within the main line. The main line will feature mostly destructive wind gust threats, with gusts potentially reaching 100-120 km/h, although localized large hail can't be ruled out.
We currently expect the most severe weather to occur between 1 to 5 PM for Eastern Ontario, ending later the further east you are. Depending on timing, we may see additional storm development behind the early afternoon line of storms if the environment recovers quickly enough before the sun goes down.
This includes Southwestern Ontario and Central Ontario, which could see pop-up storms during the late afternoon or early evening. It's questionable if they will have enough fuel to reach severe levels and may just fizzle out. However, a few of these storms could become marginally severe. This is very preliminary and subject to change once we see how the morning and early afternoon storms affect the environment.
The storm threat will end by the early evening hours across Southern Ontario, but more rain is expected to continue overnight into Tuesday morning. We could see some embedded non-severe thunderstorms overnight as well.
