Heavy Rain and Thunderstorms on the Way for Southern Ontario Starting Monday Night
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August has certainly brought its fair share of active weather to Southern Ontario, featuring a series of flash flooding incidents in areas like Peterborough and Ottawa. Our region has not been spared from other intense weather events either, with occurrences such as baseball-sized hail and tornadoes making headlines in recent weeks.
This trend of dynamic weather continues as we start off a new week, ushering in an approaching system that will bring sustained heavy rainfall and a widespread thunderstorm risk beginning Monday evening. However, it's important to note that this storm risk is not expected to include any potential for tornadoes, damaging winds, or hail, as any thunderstorm activity should remain below the severe threshold.
The main concern with this impending weather event is the possibility of substantial rainfall accumulations over the next 24-36 hours across portions of Deep Southwestern Ontario. Beginning on Monday evening, light to moderate rainfall will move into our area from Michigan, impacting regions including Windsor, Sarnia, and Chatham. Following this, heavier and more persistent rainfall is anticipated to move into these regions just after midnight.
Subsequently, the precipitation is anticipated to expand northward and eastward, reaching the Golden Horseshoe later in the evening. Rain is projected to persist on an intermittent basis throughout the overnight and into Tuesday morning. The heaviest rainfall is forecasted to be concentrated primarily in Southwestern Ontario and around Lake Ontario, encompassing Kingston. Central Ontario is likely to experience the lowest rainfall amounts throughout this event.
Rainfall is predicted to gradually diminish by late Tuesday, starting from the western parts of the region and tapering off in Eastern Ontario by Wednesday morning.
Amid the threat of heavy rainfall, we are also watching the risk of embedded thunderstorm activity, especially during Tuesday's morning and afternoon hours. The risk zone encompasses Southwestern Ontario through the GTA and along the northern Lake Ontario shoreline. However, it's anticipated that these storms will remain relatively weak and fall below severe thresholds. Nonetheless, stronger wind gusts of up to 80 km/h and dime-sized hail could occur within the more intense thunderstorms.
The heightened concern revolves around the potential for flooding due to the thunderstorm activity potentially enhancing the overall rainfall totals in localized pockets. We are currently expecting rainfall totals ranging from 30 to 60mm over the next two days in the Deep Southwestern Ontario region. However, it's plausible for certain areas to receive even higher amounts, ranging from 75 to 100mm, should they encounter multiple rounds of thunderstorms in conjunction with the system-induced rainfall.
For the Niagara and Hamilton areas, anticipated rainfall totals are expected to fall within the 20 to 40mm rage, yet these could be locally higher due to thunderstorm potential. In the GTA and areas north of Lake Ontario, the anticipated rainfall accumulation by Wednesday morning should be within the range of 15 to 30mm. Lastly, regions in northern parts of Southern Ontario spanning from Georgian Bay into the Ottawa Valley can anticipate less than 20mm of rainfall.
