Ontario's delayed-onset winter appears to have finally arrived, and parts of the province are bracing for apocalyptic levels of snowfall, now expected to produce as much as 100 cm before the weekend is out.

Unseasonably warm temperatures have come to an end, and parts of the province are on notice ahead of significant snow squalls that threaten to batter the region on Thursday, part of a multi-day snow event that could deposit huge totals on areas north of Toronto and even bring some flakes to the city.

The arrival of cold temperatures over comparatively warm Great Lakes waters is brewing a particularly concerning band of lake effect snow expected to grind large swaths of Ontario to a halt in the coming days.

Environment and Climate Change Canada (ECCC) issued warnings for portions of southern Ontario early Thursday morning, warning of heavy lake effect snowfall that will arrive Thursday evening and blanket areas along Lake Huron and Georgian Bay with" accumulations possibly exceeding 30 cm by Friday night."

The government weather agency warns that this will be no gentle dusting, calling for a multi-day snow squall event where some parts of the province can expect to experience peak snowfall rates of 5 to 10 cm per hour.

ECCC stated on Thursday that "lake effect snow off Lake Huron and Georgian Bay is forecast to strengthen this evening into Friday morning and will persist until Sunday morning."

Meteorologists predict "a very intense band of lake effect snow will affect portions of the area during the day Friday. This band may extend well inland towards Haliburton and produce high snowfall rates. The band should shift south of the regions Friday night but is expected to move back north into the area on Saturday."

Environment Canada's forecast for the storm predicts that "snowfall amounts will be highly variable" and that "some areas may receive well in excess of 50 cm by Sunday."

However, another forecast paints an even more menacing picture, suggesting that areas of Ontario will be covered by an entire metre of snow by the time the weekend comes to an end.

The latest prediction from Instant Weather Ontario notes that "persistent squalls are set to bury parts of the traditional snowbelt regions under as much as 50-100 cm of snow by the end of the weekend."

#ONStorm #ONwx ⚠️❄️ Intense Snow Squalls Could Bring Up to 50-100cm of Snow to Parts of Ontario This Weekend

📅 Thursday, November 28 - Monday, December 2, 2024

⤵️ VIEW THE FULL FORECAST:https://t.co/0CknTvnFwI

DISCLAIMER: It’s important to note that snow squalls are highly… pic.twitter.com/RhSTm6fnya

— Instant Weather Ontario ❄️ (@IWeatherON) November 27, 2024

Regardless of which forecast you trust more, it seems meteorologists are all aligned that this will be a particularly nasty snow event.

ECCC warns that such systems can "cause weather conditions to vary considerably; changes from clear skies to heavy snow within just a few kilometres are common."

The government agency stresses that "travel is expected to be extremely hazardous due to reduced visibility" as "surfaces such as highways, roads, walkways and parking lots may become difficult to navigate due to accumulating snow."

The coming snowmageddon may have snuck up on many, as it was not predicted in long-term forecasts from mid-November using the North American weather model preferred by most meteorologists in Ontario. However, a severe storm to close out the month was predicted roughly two weeks earlier using the European weather model. 

It's a discrepancy chalked up to several factors by ECCC Meteorologist Trudy Kidd, who told blogTO earlier this month that "the difference between the snowfall forecast between the European and North American models likely comes down to several factors."

"There are differences in model resolution. There are different physics in how they handle certain conditions, but even small differences in the initial conditions that are put into the model can lead to large variances in the forecast once you have a longer lead time, because those little changes or differences between various models become amplified over time."

Kidd noted that "a drastic divergence between what the models have" is not uncommon when tracking events two weeks away "and there are just so many factors at play."

"Sometimes, especially when it comes to winter weather forecasting, you can even see big differences a week in advance," Kidd continued, adding that "we can be pretty confident that as we move closer to the event start to that day, the weather models will converge" — exactly what occurred in this case.

The coming snow event may signal the first of many snowy days to come, which some may find a welcome change from the balmy winter experienced in Southern Ontario in 2023-24.

ECCC meteorologist Geoff Coulson told blogTO on Wednesday that "more than a few people that enjoy winter activities were disappointed by how warm last winter was, consistently through the course of the whole winter," but noted that "this winter is shaping up to be more of a traditional one."