The leading edge of a nasty winter storm is already frosting Toronto streets with the first layer of what could soon be a dense blanket of snow, and the already dangerous forecast has been upgraded for the worse.

An Environment Canada snowfall warning for the City of Toronto issued on Tuesday was upgraded late Wednesday morning.

Like the warning that came the day before, the government weather agency still cautions of snowfall accumulations up to 15 to 20 cm, reduced visibility, and isolated power outages.

Environment Canada warns that "a Texas low will bring heavy snow to the area beginning early this afternoon," which should "taper off to flurries Thursday morning."

EnvironCan adds that rush-hour traffic will see a "significant impact" and "encourages everyone to make an emergency plan and get an emergency kit with drinking water, food, medicine, a first-aid kit and a flashlight."

Snowfall warnings are in effect across southern Ontario as Wednesday's storm will bring some of the heaviest snowfall totals of the year so far.

A widespread 10-25 cm is expected through Thursday. #ONStorm #ONwx #TWNStormCentre

— The Weather Network (@weathernetwork) January 25, 2023

As ominous as that forecast looks, other areas of Ontario could see even more of the white stuff, with localized snowfall as high as 30 centimetres along a stretch that includes Kingston and Ottawa.

10am Storm Update: Snow has moved in across much of southern Ontario. Intensity will increase later this afternoon. 15-20cm Hamilton to Toronto, 25-30 Kingston, Ottawa and Montreal. #onstorm pic.twitter.com/md2NrqHmwk

— Anthony Farnell (@AnthonyFarnell) January 25, 2023

A band along the northeastern shores of Lake Ontario and the western banks of the St. Lawrence River will see the worst of the storm, including through a busy stretch of the Highway 401 corridor.

Though snowfall accumulation won't be quite as severe in Toronto, the city and surrounding areas will see more snow than areas to the north, falling within a larger band of snowfall concentrated along the north side of Lake Ontario.

Those west of the GTA should watch out though, as this will be another area of particularly dense snowfall.

❄️❄️ UPDATED SNOWFALL TOTALS ❄️❄️
for today through Thursday. Amounts up to 25 cm are expected locally for Halton-Peel and near Kingston. This evening's commute will be impacted for many areas.
Link to alerts 👉 https://t.co/Sk69Or0svY#ONstorm #ONwx pic.twitter.com/OAzmH9wRrx

— ECCC Weather Ontario (@ECCCWeatherON) January 25, 2023

Even if reality falls well short of the forecasts, this winter storm is almost certain to shatter records for Jan. 25 snowfall. Toronto only has to exceed a rather low 7.8 centimetres to break a record that has stood since 2005. It's possible the city could triple that record today.