Lake Effect Snow Targets Parts of Southern Ontario With Over 20cm of Snow Possible by Thursday
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Environment Canada has issued widespread snow squall warnings around Lake Huron and Georgian Bay today. The warning was issued because of the current frontal squall sweeping through the region, coupled with additional lake-effect snow expected to develop later today, persisting into Thursday morning.
Our forecasts often highlight the variability of snowfall totals during snow squall events due to the narrow bands involved. It's not uncommon for one area of a town to experience significant snowfall while an area just 5-10 minutes away receives barely any snow.
Predicting the precise location of these snow bands is challenging as even a slight shift in wind direction can significantly impact the outcome. Typically, we can provide a general idea of which regions will be most affected.
However, this occasion is different, and we will not be producing our standard polygon forecast map. The three main high-resolution models we rely on for lake effect snow forecasts, HRRR & NAM from the United States and Canada's HRDPS. These models are showing significantly different outcomes, making it impossible for us to offer a forecast with confidence. We believe it wouldn't be responsible to predict something we're not sure about.
Instead, we're sharing the raw model data from these three models, allowing you to see the range of potential scenarios for your location and prepare accordingly. It's important to remember that model data often overestimates actual snowfall, so the amounts shown are likely too high. However, this data is useful for understanding where each model predicts the heaviest snowfall will occur.
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The models mainly diverge regarding the Georgian Bay squall expected to develop this evening and continue into Thursday morning. This squall is predicted to come ashore between Wasaga Beach and Collingwood, extending inland towards Barrie and possibly reaching the northern York Region.
The HRRR model estimates the most snow from this squall, suggesting over 50cm in areas just southwest of Barrie, including Wasaga Beach, Angus, and Alliston.
Keep in mind, that this is just raw model data, and the estimated 50cm is probably an overestimation, especially since the HRRR model tends to overpredict lake effect snow events. Nevertheless, if the HRRR model is accurate, this region could see 20-40cm of snow by Thursday.
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On the other hand, the NAM and HRDPS models predict a much weaker squall off Georgian Bay, with snow totals more in the range of 5-10cm (locally 15cm), and the NAM showing barely a few centimetres. This illustrates the wide variety of potential outcomes, from a few centimetres to over 20cm of snow.
Regarding the Lake Huron shoreline, there is slightly more consensus on overall accumulation, with all three models predicting over 20cm of snow between Hanover and London. However, this prediction still represents a very narrow band, meaning not everyone will see significant snow, and some may see only a few flakes.
Southern Grey and Bruce counties, along with Huron and Perth counties, are expected to bear the brunt of the heaviest snowfall, with totals ranging from 10-20cm and localized pockets possibly receiving 25-30cm. This includes areas like Kincardine, Goderich, Hanover, Listowel, Wingham, and Stratford. The Kitchener and Guelph region may also experience bursts of heavy lake-effect snow, with accumulations ranging from 5 to 10cm.
Further south, all models concur on another band of lake effect snow southeast of Lake Huron, stretching from Grand Bend to the London area. This band is not expected to be as prolonged or intense as those further north, so snowfall totals will be more in the range of 5 to 10cm by Thursday afternoon.
As the lake effect snow winds down by Thursday's end, our focus shifts to a system arriving late Friday into Saturday that could bring significant snowfall to parts of Southern Ontario. There's some disagreement on the exact path of the system, and temperatures will hover near the freezing mark, potentially leading to mixed precipitation in some areas, affecting overall snowfall totals.
At this stage, a widespread snowfall of 10-20cm, with local amounts up to 25cm, seems fairly likely in parts of Southwestern Ontario and possibly extending into the Golden Horseshoe. We will issue a preliminary forecast soon, so stay tuned for updates!
