A large portion of the province might want to keep those flashlights on hand overnight Wednesday, as freezing rain described as 'hazardous' threatens much of Ontario and parts of Quebec.

A large area stretching east from Clarington past Montreal and north to Ottawa to just south of North Bay is painted red on Environment and Climate Change Canada's (ECCC) Weather Alerts map, with warnings of several hours of freezing rain and possible ice accretion up to a dangerous 5-10 mm by Thursday morning.

The system will be less potent in the eastern GTA area, where freezing rain is expected to pass by the evening hours. A potentially hazardous ice accretion of 2 to 5 mm is expected, and ECCC has stated that Ontario residents should be prepared "as utility outages may occur" and should "consider postponing non-essential travel."

A hazardous freezing rain event is expected beginning this afternoon into Thursday morning. 🧊

⚠️ Be prepared especially in the greater threat area as utility outages may occur and consider postponing non-essential travel. ⚠️

Alerts: https://t.co/bVdx0NGPlu#onstorm #onwx pic.twitter.com/MYx1WxyUaV

— ECCC Weather Ontario (@ECCCWeatherON) January 24, 2024

The government weather agency warned on Wednesday that "patchy freezing drizzle will affect the [southeastern Ontario] area today before a more significant area of freezing rain arrives this afternoon," adding that areas closer to Lake Ontario may get off easier than those further north and east.

Regardless, hazards include icy surfaces and roads, and the potential for ice buildup to weigh down power lines and break tree branches — both major sources of utility outages.

The situation looks much more menacing out in the Ottawa and Montreal areas, where ice buildup of up to 10 mm is expected before Thursday morning.

The Weather Network reports that people in this area can "expect the icy conditions to linger through Thursday morning, with near 10 hours of icing possible."

Ten millimetres is indeed a dangerous level of ice buildup, but it is still just a fraction of the accretion left by more significant storms in past decades.

A 2013 ice storm that encased much of Ontario in a layer of deep freeze left behind a maximum accretion of about 30 mm, while the devastating 1998 ice storm deposited up to 100 mm — or ten times the expected ice accretion for this coming storm — on parts of Quebec.