Extreme temperature dip, blinding snow squalls and flash freezing on tap for southern Ontario

Sunday, January 5, 2014, 8:31 PM -

STORM WATCH: Tune in on TV as we track this major system's approach.

People across southern Ontario should prepare for a wide range of precipitation depending on where they are, accompanied by a very rapid drop in temperatures that will make for a lot of icy roads.

Northerly communities are on track for mainly snow, while warm air will nose into the GTA, Golden Horseshoe, and Niagara overnight with precipitation mixing to ice pellets or freezing rain, then to rain. Areas north and west of the GTA will remain all snow overnight with the heaviest falling in a line from Windsor to Parry Sound to Pembroke.

That precipitation switchover prompted forecasters to warn drivers to be especially mindful of the roads, especially for travellers heading north.

RELATED: The Weather Network's Chief Meteorologist Chris Scott breaks down this messy system.

Many people in Ontario were waking up to some minor snowfall amounts, but the real show was set for the evening hours.

"The snow through southern Ontario will start through the afternoon moving into the GTA for the evening," Weather Network meteorologist Matt Grinter said early Sunday morning. "Through the late evening, the snow will switch over to a mix of rain or freezing rain for the Golden Horseshoe into eastern Ontario and southern Quebec."

Those areas of the province that are on track for snow could see as much as 25 cm.

Southeastern Ontario and southern Quebec has a greater risk of freezing rain overnight tonight to early Monday morning, before changing to rain.

But in the areas where mixing occurs, a very drastic fall in temperatures will result in roads slippery with ice by the morning, although any freezing rain periods should only last for a few hours - nowhere near the extreme amounts that occurred during last month's ice storm.

"Temperatures will fall very rapidly across the GTA (between 4-6 am), with the potential for a flash freeze on wet surfaces and untreated roads." says Gina Ressler, another meteorologist at The Weather Network. "Main precipitation will exit GTA by this time, but very cold air will enter in it's wake."

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The rapid cooldown will be accompanied by lake effect squalls, setting up with northwesterly winds, quickly switching to westerly winds, continuing through to Wednesday.

Temperatures will continue to drop through the day on Monday, with dangerous wind chills and potentially record-breaking low temperatures early Tuesday. Windsor's all-time low temperature record and wind chill record are in jeopardy Tuesday morning.

Interestingly, southwestern Ontario (Windsor to London) will be colder than southeastern Ontario (Toronto to Ottawa) Tuesday morning. And not only will Tuesday be cold, but winds will be very brisk, causing extreme wind chills and dangerous snow squalls off Lake Huron and Georgian Bay.

In wind chills -30 to -40, frostbite can occur in 10-30 minutes, and hypothermia is a significant risk for those improperly dressed. Snow squalls will make driving treacherous. 

Environment Canada has issued a strongly-worded bulletin advising those in the Snowbelt areas to avoid driving on Monday/Tuesday: 

"The combination of a fresh heavy snowfall from tonight's storm with intense snow squalls on Monday with bitter wind chills poses a life-threatening risk for anyone outside for any duration, or stranded in vehicles if roads becomes snow-blocked. Travellers need to ensure they have an adequate car emergency kit and ample fuel if travelling any distance"

The good news is that temps will slowly rise after Wednesday. It's looking likely that we'll see temps above zero by the weekend.

For an in-depth look at what's behind the storm, check out this analysis by Chief Meteorologist Chris Scott.