Winter has flipped the switch across Ontario this week as periods of snow and plunging temperatures begin to settle in. A weak clipper system will bring some widespread snow across the region through Thursday, with more potent lake-effect snow expected to target the traditional snowbelts into Saturday. Winter travel advisories and snow squall watches are in effect, with drivers being urged to postpone any non-essential travel until conditions improve. In terms of the system snow, much of the Greater Toronto Area will be spared, with the heavier accumulations falling for areas closer to Lake Huron. More on the snow timing, plus a look at the colder conditions as we head into the weekend, below.
Weak clipper system will bring a widespread snow to Ontario through Thursday
Temperatures rise well above freezing Thursday afternoon ahead of a colder weekend ahead
Eyes on a possible Colorado low early next week, as temperatures remain on the cold side of seasonal
THURSDAY: PASSING CLIPPER BRINGS PERIODS OF SNOW AHEAD OF FALLING TEMPERATURES
Southern Ontario saw a dash of lake-effect snow earlier in the week, and some of its coldest temperatures this season so far on Wednesday.
While temperatures will be milder across the south once again on Thursday, the effects of a weak clipper system will still be persistent for parts of the day as periods of snow continue to impact central and eastern sections of the province.
The snow will diminish from west to west throughout the day, with the heaviest amounts expected near the shores of Lake Huron and Georgian Bay, where there will be a bit of lake enhancement.
Snow squall watches are in effect, with visibilities expected to be significantly reduced due to the heavy, blowing snow.
"Consider postponing non-essential travel until conditions improve," Environment Canada warns.
In all, around 5-10 cm is expected for central Ontario, accompanied by gusty winds up to 50 km/h. Areas south of cottage country will see around 3 cm of snow or less, with the higher totals staying primarily north of Highway 401/407.
Across the GTA, there's the potential for both the sunshine and temperatures to overachieve for several hours, ahead of the cold front that arrives later in the day.
"But the strong and gusty winds will keep things from feeling all that enjoyable," says Weather Network meteorologist Dr. Doug Gillham.
The cold air will begin to pour into southern Ontario Thursday night, with a quick burst of heavy snow possible along the arctic front through the pre-dawn hours.
FRIDAY: POTENTIAL FOR POTENT SQUALLS
With the colder air in place and a northwest flow getting re-established across the region, lake-effect snow bands will re-develop for Friday primarily for the snowbelts, but reaching into parts of the GTA at times as well.
Poor travel conditions are likely Friday and Saturday across most main highways through the Grey-Bruce and Huron-Perth regions, particularly Highway 21, Highway 8, and portions of the 401 between London and Cambridge. Conditions will also deteriorate along the 400 from the northern GTA through Barrie and Orillia.
As with most snow squalls, accumulations will be highly variable, but some areas through Grey-Bruce and Huron-Perth could see some significant accumulations into Saturday.
WEEKEND: COLDEST AIR OF THE SEASON SO FAR SETTLES IN
A more persistent cold pattern will begin on the weekend across the south, with the threat for some of the coldest temperatures of the season so far. The city of Toronto for example, could actually reach -10°C for the first time this winter.
"If this happens, it will be at least 20 days after the previous latest first -10°C day (Jan. 3, 2016)," says Gillham. "Only twice on record have we gotten into January without having dipped to -10°C and yet this year we are going to get over three weeks into January without reaching -10°C."
While much colder than we've seen, this weekend's temperatures are more typical of late January and really won't be all that far off of seasonal values.
EYES ON POTENTIAL HIGH IMPACT STORM NEXT WEEK
Beyond the weekend, forecasters are watching the potential for a Colorado low to approach or track south of the Great Lakes region early next week.
"One scenario keeps the storm well to our south with little to no snow for the Golden Horseshoe. However, it is possible that this storm will track further to the north and become a high impact winter storm for much of southern Ontario," says Gillham, adding that computer models currently range from no snow at all to 10-20+ cm of snow. "Please check back for updates."
Near to slightly below seasonal temperatures are expected to dominate next week.