First rain then snow, seasons change in a hurry across southern Ontario

·3 min read
First rain then snow, seasons change in a hurry across southern Ontario
First rain then snow, seasons change in a hurry across southern Ontario

After days of rare November sunshine and even a few 20-degree daytime highs across southern Ontario this week, a pattern change is on the doorstep for the province. Winter has arrived in a hurry across the far northwest, with a potent storm bringing as much as 40-50 cm of snow to some areas through Friday, while in the south, the abundant sunshine gives way to rain and gusty winds moving in later Thursday. Much colder weather this weekend could also result in bands of lake-effect snow, with locally heavy snow totals possible for the traditional snow belts. More on the timing of these systems and potential impacts, below.

THURSDAY INTO FRIDAY: TRAVEL NOT RECOMMENDED ACROSS THE NORTHWEST, RAIN PUSHES INTO THE SOUTH

Two low-pressure systems have joined forces to bring very heavy snow and strong winds to parts of the eastern Prairies, spreading across the border into northwestern Ontario as well. Widespread snowfall and winter storm warnings are in effect.

MUST SEE: Travel not recommended for parts of the Prairies, NW ON as potent storm hits

"Rapidly accumulating snow could make travel difficult over some locations. Prepare for quickly changing and deteriorating travel conditions. Visibility may be suddenly reduced at times in heavy snow," says Environment and Climate Change Canada in the winter storm warning.

prsnow (11)
prsnow (11)

For Thunder Bay and the shores of Lake Superior, the precipitation will manifest as rain and will quickly pick up through Thursday and into early Friday. A narrow swath around the lakeshore could see 50-75+ mm of rain fall. As you travel farther away from the lakeshore, snow will be the dominant precipitation type, with as much as 50 cm of snow threatening the hardest hit places, particularly between Sioux Lookout and Dryden.

Travel along Highway 17 will be treacherous, as gusty northeasterly winds between 70-90 km/h will make for poor visibility and slippery road conditions Thursday through Friday afternoon.

Southern Ontario on the other hand will see the tempered, but prolonged and varying effects of the system, beginning Thursday night and continuing through Saturday and Sunday, when lake-effect rain and snow develop once again.

onqcrain (8)
onqcrain (8)

Rain will develop on Thursday night from the eastern shores of Lake Superior, all the way through cottage country, the Greater Toronto Area and southwestern Ontario. By Friday morning, the leading edge of the rain reaches Ottawa, while the back edge is pulling out of the GTA.

Conditions will improve across much of southern Ontario on Friday, with a southerly flow allowing for double-digit highs near 12 or 13°C.

PHOTOS: Ontario basks in November patio weather as temperatures soar

"But this is when the transition begins," warns Nadine Powell, a meteorologist at The Weather Network. "This is a huge low-pressure system that will generate cooler westerly winds this weekend."

ONPatternPrecip (1)
ONPatternPrecip (1)

WEEKEND: INCREASING POTENTIAL FOR WIDESPREAD WET SNOW SUNDAY NIGHT

Light rain is expected across southern Ontario and the GTA on Saturday, but as temperatures cool Saturday night into Sunday morning, higher terrain inland from Lake Huron and Georgian Bay can expect a wet snow mix.

A surface trough behind the departing low will bring light rain showers across much of southern and central Ontario Sunday afternoon, but by late day, a mix with wet snow is expected for parts of central Ontario and the higher terrain northwest of Toronto. Some accumulations are expected above the escarpment and away from the Great Lakes, though with little to no accumulation expected for the GTA.

Chilly, near seasonal, weather will continue into early next week, with temperatures set to rebound to above seasonal for a couple days during the middle of the week before colder weather returns late in the week or weekend once again.

Be sure to check back for the latest updates on the changing pattern across Ontario.

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