A storm forming off the Northeast U.S. coast tonight will brush Nova Scotia with some snow late tonight through midday Tuesday. The highest accumulations will run along the south coast and up toward Cape Breton.
The storm will then take aim at Newfoundland Tuesday through Tuesday evening with significant snowfall across the southern half.
Lake-effect snow will be an issue for some as the coldest air of the season crosses the lakes. It's a very tough forecast as winds will be constantly shifting and there will also be a surface trough laying WNW to ESE from Lake Huron into New England that will also focus a band of heavier snow.
The map below shows the snowfall forecast valid from this evening through Tuesday. This does not include snow from earlier today. There will be additional rounds of lake-effect snow into the middle of the week.
My best estimate at this time is that there will be a narrow band of heavier snow setting up somewhere from the Bruce Peninsula through the Owen Sound area then to near Collingwood later tonight.
After 4 a.m. or so, that band will weaken and a second lake-effect band sets up somewhere near Saugeen Shores and perhaps extending into the Hanover/Mt. Forest area into the morning then slowly shifts south toward Kincardine and over to Listowel. Under this band the snow could be quite heavy with dangerous travel conditions. Again, very tough forecast to pinpoint these bands through tomorrow.
The map below shows how cold it will feel (on average) during the afternoon Tuesday after you factor in the wind and other elements.
Temperature departures (F) for Thursday morning
Midweek clipper storm
A classic Alberta clipper will dive southeastward Wednesday and will bring accumulating snow from northern Alberta (Wed) through southern Sask. (Wed night) into southern Manitoba (Thu). Look for a general 6-12 cm with this feature.
This same feature could spawn another coastal storm later in the week, perhaps leading to the possibility of significant snow from eastern New England through Nova Scotia Friday night and Saturday.
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My latest interpretation of the ECMWF forecast model, along with some input from other models and current data.
Some thoughts on the weather pattern into mid-July
Wildfire smoke causing significant problems across Saskatchewan.
Spring-like storm to soak parts of eastern and Atlantic Canada this weekend as the West cooks.
Heat wave for western Canada by the weekend as the East cools down a bit.
Severe weather threat Monday evening/night for Ontario. Building heat wave late this week into next week out West.