The first alarm bells are beginning to sound for an ice storm across southern Ontario. The necessary ingredients look to align to produce freezing rain, a wintry mix, and heavier snowfall farther north on Wednesday and Thursday.

A frigid trough sliding across northern sections of Ontario and Quebec by Wednesday will provide ample cold air at the surface for the winter storm. At the same time, an anomalously warm air mass is bubbling up across the Deep South.

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This is where we have a problem. That Arctic high pressure across Ontario and Quebec means the approaching Colorado low has no escape route. The surface winds will blow out of the northeast, meaning temperatures at the surface are forecast to stay below freezing.

The air aloft will soar above the freezing mark near Lake Erie as the low crosses the Ohio Valley Wednesday night.

Everyone in southern Ontario needs to be on guard for a winter storm later Wednesday, but the farther south you are, particularly along and south of Highway 401, is where to watch the building threat for an ice storm. Gusty winds out of the northeast may enhance the threat of power outages through Thursday.

Farther north, ice pellets will dominate with a shallow layer of mild air off the surface. A healthy swath of snow across cottage country and eastern Ontario is in the cards.

Stay tuned to The Weather Network in the coming days as the details come into focus ahead of this potentially impactful storm across southern Ontario.