ONTARIO: Thunderstorm Forecast for Thursday, August 24, 2023
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For Southwestern Ontario, the rhythm of thunderstorms seems unending as the region experienced a relentless night of storm activity, delivering a soaking 100-200mm to Windsor and Essex County. Unfortunately, the storm saga continues, as a second day of potential severe weather awaits Southern Ontario on Thursday afternoon and evening.
Confidence is growing in what might shape up to be a potentially hazardous day, particularly in Deep Southwestern Ontario, with potential extensions into parts of the Golden Horseshoe. The stage is set for strong severe storms, with a favourable environment likely to unfold starting from the early afternoon hours.
Fresh data suggests that the overall storm threat could surpass initial expectations. In response, we've introduced a ‘significant’ severe risk zone specifically focused on Deep Southwestern Ontario. The reasons behind this upgrade include the threat of wind gusts reaching up to 120 km/h and an elevated tornado risk. While the primary concern revolves around the potential for destructive wind gusts, it's worth noting that the possibility of large hail up to the size of golf balls can't be dismissed, particularly within isolated early-day storms.
Key questions surround the precise location of storm initiation. Initial models indicated storms emerging over Michigan during the late afternoon hours and subsequently crossing into Southwestern Ontario by evening. However, the latest trends depict a line of storms developing from the Western GTA, extending through Kitchener and over Lake Huron.
As this evolving line of storms descends southward, it will encounter a prime environment over Southwestern Ontario, which may spur rapid intensification. Timing still holds a degree of uncertainty, with the possibility of storms being pushed to a later evening occurrence. However, this shift doesn't seem likely to influence the severity of the events.
Further storm development is also possible over Michigan, impacting Deep Southwestern Ontario. In this scenario, a wide-ranging complex of storms could sweep the region with robust damaging wind gusts spanning 100-120km/h, during the late evening into the early overnight hours. While the tornado and hail risk is anticipated to be more pronounced as storms initially form, the focus may later shift to a wind-driven threat as the day progresses. This variable risk hinges on the potential storm appearance over Michigan.
We've incorporated an ‘isolated strong tornado’ risk specifically for the Windsor and Chatham regions. This risk hinges on storm development in proximity to the border and their subsequent trajectory into Southwestern Ontario during the height of the tornado risk. In either case, the possibility of tornadoes remains a significant concern.
Amid these dynamics, the concern for flash flooding is in the spotlight, particularly in areas that witnessed substantial rainfall on Wednesday and Thursday morning. The prospect of an additional 50-100mm of precipitation further accentuates localized accumulation, potentially totalling 200-300mm within two days.
Moving beyond Deep Southwestern Ontario, the severe threat extends to portions of the Golden Horseshoe, including the Niagara and Hamilton regions, which have a ‘slight’ severe risk. Some data points to isolated storm development in the late afternoon and evening, possibly bringing in hail of ping pong ball size, wind gusts reaching 100 km/h, and the potential for an isolated tornado. As always, stay vigilant, keep an eye on updates, and stay safe.
