Environment Canada says a blast of arctic air hitting southern Ontario by Sunday night will usher in the coldest weather so far this winter.

The weather agency says residents can expected a "deep freeze" as the work week begins, with temperatures plunging to -20 C in some parts.

Snow squalls are also forecast in southwestern Ontario.

Story continues below advertisement

Environment Canada has also placed a stretch of the province from the Grey-Bruce area to east of Ottawa under freezing rain and winter storm warnings.

Provincial police are advising drivers to take caution while air travellers are advised to check their flight status ahead of time.

Hamilton has issued a cold alert effective Sunday night and other cities are likely to follow.