From Record-Breaking Heat to Blizzard; Snow Squalls Could Dump Upwards of 15-30cm on Parts of Ontario by Thursday
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The last 48 hours have been a weather whirlwind across Southern Ontario, beginning with thunderstorms and the season's first 20°C temperature recorded in Windsor on Tuesday.
This brief 'heatwave' has abruptly ended, ushered out by a sharp cold front that sent temperatures tumbling on Wednesday. By overnight into Thursday morning, we're bracing for wind chills that could make it feel like it's in the -20s!
The return of Arctic air to Southern Ontario typically means one thing: Mother Nature is about to fire up the lake effect snow machine over the usual snowbelt regions. The upcoming day will be no exception as we anticipate intense snow squalls affecting the Lake Huron and Georgian Bay shorelines, potentially dumping 15 to 30cm of snow by Thursday's end. Accompanying the heavy snow will be strong wind gusts, leading to blowing snow and localized blizzard conditions over the next 24 hours.
The cold front in question has already made its way across our region as of early Wednesday afternoon, with temperatures in Southwestern and Central Ontario swiftly falling below freezing. This trend is expected to persist, bringing even colder air by evening.
Lake effect snow is set to begin this afternoon, initially starting off as disorganized and light. Expect light to moderate snowfall along the Lake Huron and Georgian Bay shorelines through the afternoon and evening. In Northeastern Ontario, snow squall activity is underway, focusing on the southeastern shoreline of Lake Superior between Wawa and Sault Ste. Marie.
As we move into Wednesday evening, models predict a more intense, focused squall developing between Wiarton and Kincardine, extending over Georgian Bay to come in land around Simcoe County. The Sault Ste. Marie region will also face relentless snow squall activity through the evening and overnight.
This squall is particularly noteworthy due to its significant moisture content, benefiting from an optimal fetch across Lake Superior, Lake Huron, and Georgian Bay. Consequently, we expect high snowfall rates, with the potential for the band to reach far inland, possibly affecting parts of the Northern GTA.
Driving conditions in Grey, Bruce, and Simcoe Counties, among other regions, will become treacherous overnight into Thursday morning. With wind gusts of 60 - 80 km/h, near-zero visibility and rapid snow accumulation are anticipated, raising the possibility of highway closures overnight.
Further south, areas away from Lake Huron like Listowel and Hanover may experience more scattered, less intense lake effect snow compared to the squall to the north.
By sunrise on Thursday, the main snow squall is expected to begin dissipating, although it will likely persist through the morning and early afternoon. The shifting wind direction may cause the squall to drift, dispersing snowfall over a broader area.
Lake effect snow activity off Lake Superior and Lake Huron/Georgian Bay is anticipated to wind down by mid to late afternoon on Thursday, as a slight temperature rise creates conditions less conducive to lake effect snow development.
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Snow Squall Accumulation Disclaimer
Forecasting the exact snowfall accumulation for a specific location in a lake-effect snow event is extremely challenging. This is because of the highly localized nature of snow bands, which can lead to significant variance in totals even over short distances.
Therefore, you may notice our forecast shows significantly more snow than your weather app (including our own app). App-based forecasts often struggle with lake effect snow events due to their localized nature and reliance on data focused on larger macro-level weather events. This results in a failure to accurately capture the squalls, which operate at a micro-level, leading to intense snowfall totals.
Our forecast may still be off if the wind direction varies slightly from what the models predict, causing the snow squall band to form further north or south. That's why our forecasts use broader zones to account for this variability, meaning not everyone within these zones will see the significant totals. Essentially, we're indicating that a location within this area could see the forecasted amount.
The areas hardest hit in Southern Ontario are expected to be Wiarton, Owen Sound, Chatsworth, Meaford, Collingwood, and Barrie, with 15 to 30cm of snow accumulation possible by Thursday's end.
It's important to note that models significantly diverge on the strength of these squalls, with some indicating potential for up to 50cm of snow in localized areas. Thus, there's a possibility for some regions, especially if the squall remains stationary overnight and into Thursday morning, to experience higher than anticipated snowfall totals.
Surrounding areas such as Port Elgin, Hanover, Keswick, and Orillia are generally expected to see 10 to 20cm, although the snow accumulation gradient will be extremely tight, meaning some areas may see little to no snow.
Less than 10cm of snow is forecasted for the rest of Southern Ontario, with accumulations above 5cm confined to regions east of Lake Huron and around Lake Simcoe. Durham region could approach 10cm of snow, depending on the inland reach of the Georgian Bay snow squall. Eastern Ontario and the Golden Horseshoe are expected to see less than 2cm of snow.
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In Northeastern Ontario, snow from a system will continue affecting the northern regions, including Timmins, Kapuskasing, and Cochrane, with 20 to 30cm of snow possible.
Lake effect snow will be more localized, with Sault Ste. Marie anticipated to receive 15 to 30cm of snow before the squalls taper off late Thursday. The rest of Northeastern Ontario can expect widespread totals of 5-15cm, with some areas seeing up to 20cm.
