Heavy rain, snow, 20 degree temperature drop in store for Ontario, Quebec

Saturday, April 12, 2014, 10:25 PM -

Winter will clash with spring over the next few days, as a slow-moving frontal boundary sets up across southern Ontario and Quebec. 

Significant rainfall is expected along the boundary, with 20°C temperatures and a risk of thunderstorms to the south. 

A vigorous cold front will sweep across the region by Tuesday morning, changing the rain to wet snow, and ushering in much colder air.

ONTARIO STORM: Six things you need to know

WHAT TO EXPECT 

Rain will spread across southern Ontario late Sunday afternoon, reaching southern Quebec late evening. 

"Several waves of moisture will surge across southern Ontario and Quebec over the next three days," says Weather Network meteorlogist Gina Ressler. "The heaviest rainfall will occur in northern Grey-Bruce Country, and northeast of Georgian Bay into Quebec, where some communities can see 50 to 75 mm of rain." 

CLICK BELOW TO WATCH: Severe storms pushing in from the U.S.; prompt warnings north of the border

STAY TUNED: Be sure to check The Weather Network for updates as this system approaches. Thunderstorm warnings may be issued.

Rainfall accumulations will drop off sharply to the south, adds Ressler. 

Saturday night through Sunday morning, the rain-snow line will lie near Sault Ste Marie – Sudbury – north of Montreal. 

The rain-snow line will lift farther north Sunday afternoon to Monday morning as warm air surges in.

Temperatures are expected to hit the low 20s in southwestern Ontario on Sunday, and in southeastern Ontario and southern Quebec on Monday. 

RELATED: Southern Ontario could get hit with up to 25 mm of rain next week

In the warm sector, the air will likely become unstable enough to spark shower and thunderstorm activity Saturday night through Monday.

SNOW 

Monday night through Tuesday morning, a vigorous cold front will sweep across the region, changing the rain briefly over to wet snow before clearing.

Snow is possible as far south as North Bay, with the heaviest amounts expected in the Nickel Belt in a band reaching across the shores of Lake superior. 

Around 5-10 cm is expected in the worst-hit areas, with locally higher amounts. 

The snow may begin as rain in some more southerly areas, followed by a transition period of mixing before it becomes full-on snow as overnight temperatures drop.

TEMPERATURE DIVE 

More notable will be the drastic drop in temperatures behind the cold front, with afternoon high's on Tuesday more reminiscent of late February than April. 

"Currently, the forecast for Toronto, has scattered thunderstorms Saturday evening and Sunday -- as the warm front lifts to the north -- with temperatures near 20°C, but feeling like 22," said Brian Dillon, another meteorologist at The Weather Network Saturday evening. "However, a sharp cold front sliding through Monday night will drop temperatures to a daytime high of to 2°C, feeling like minus 4 on Tuesday."

WINDS 

Gusty winds are expected across southern Ontario Sunday afternoon, but even more so for Monday afternoon/evening, ahead and along the cold front. 

IN DEPTH: Read Dr. Doug Gillham's analysis of this latest battle between winter and spring.

This comes at a time when the eastern Ontario town of Belleville is under a state of emergency due to flooding from the spring melt. 

Environment Canada warns of localized flooding ahead of this system and are urging the public to stay away from creeks and river banks at this time. 

SEE ALSO: Belleville braces for flooding as state of emergency continues

Widespread watches and warnings are in effect. See the full list, here.