Very Isolated Risk For Marginally Severe Thunderstorms in Eastern Ontario and Parts of Northeastern Ontario

The last few weeks across Southern Ontario have certainly felt like fall with temperatures near the freezing mark and even some areas have seen the season’s first snowflakes. Although summer isn’t done just yet with one more day of well above seasonal temperatures expected on Friday. There is also the threat of severe thunderstorms as a cold front cuts across the region bringing the potential for damaging wind gusts, large hail and even an isolated tornado can’t be ruled out.

Friday will start off as quite warm by late October standards when you wake up with temperatures in the low teens across much of Southern Ontario. Even warmer air will work its way into the province from south of the border later in the day with many areas reaching into the low to mid-20s by late afternoon. In fact, almost everyone except for Northern Ontario and the higher elevations around the Algonquin Highlands will see temperatures between 20-25°C sometime during the day on Friday.

The late summer-like temperatures will be only temporary as a sharp cold front moves across the region later in the day. This will cause a very rapid drop in temperatures during the evening hours with many areas going from the upper teens or low 20s into the lower single digits in only a matter of a few hours. Some models suggest that we could see temperatures drop by 10°C or more within only one hour! Fortunately, we aren’t talking about a drop in temperatures to below the freezing mark so a flash freeze won’t be an issue as is usually the main concern with such a quick drop in temperatures.

Aside from the rapid plunge back into fall, we also expect to see a line of strong to severe thunderstorm develop ahead of the cold front during the late afternoon and early evening. The highest chance of severe weather will be along the Lake Huron and Georgian Bay shoreline as the storms move in from Michigan around the dinner hour. These storms have the potential to produce damaging wind gusts between 80-100km/h and up to quarter size hail along with heavy rainfall and frequent lightning strikes. We can’t rule out an isolated tornado from these storms which would only add to the record-breaking tornado season we’ve experienced this year. The storms will slowly weaken during the evening as the line tracks to the east with daylight heating slowly disappearing. So areas east of a line roughly from Petawawa and Brantford should see only non-severe thunderstorms by the time the line reaches them.

As we head into the weekend, temperatures will return to what we normally see during the late fall with most areas just a few degrees above the freezing mark on Saturday morning. Further north through parts of Northern and Central Ontario temperatures may drop below the freezing mark. This will continue into next week as we closely monitor the potential for more areas to experience their first snowfall of the season including parts of Eastern and even Southwestern Ontario. Although we’ll likely have to wait a few more weeks to see any noticeable accumulation. More details on that to come.