Our forecast team is putting the finishing touches on this difficult forecast as the first widespread major winter storm of the season hits Ontario and Quebec. Here are some things to watch for:
Areas north and west of a line from Kincardine to Barrie to Pembroke will see the heaviest snow with the Bruce Peninsula, Parry Sound, Huntsville, North Bay and Mattawa likely seeing more than 20 cm (possibly near 30 cm in some places) by Sunday night.
In the London-Kitchener-Toronto corridor, the 401 will be the approximate dividing line between rain to the south and snow to the north when the heavy precipitation hits on Sunday morning. This rain-snow line will likely lift north of highway 7 for areas east of Guelph during the afternoon. The amount of wet snow that accumulates will vary greatly across the GTA with the lakeshore in Burlington likely seeing very little accumulation while Orangeville, Aurora and Uxbridge may see a substantial amount of heavy wet snow.
Where the precipitation remains as heavy wet snow for most of the storm on Sunday, there may be problems with the weight of the snow on tree branches.
Eastern Ontario and Southern Quebec will see a mix of all precipitation types, and we still expect that some freezing rain could fall in the Ottawa and St. Lawrence valleys on Sunday afternoon before turning to rain.
Severe snow squalls on Monday will be affecting highway 402 west of London. If the wind stays more northerly, this would reduce the potential for large accumulations in London and lessen the impact on Monday driving along highway 400.
The Maritimes will see 50-100 mm of rain by Tuesday which may lead to localized flooding.