Fog patches are in the forecast for Toronto after a night of heavy rain.

Environment Canada says the forecast calls for some periods of rain on Saturday morning that will change to periods of snow mixed with rain. Fog patches will roll into the city on Saturday afternoon before dissipating by Saturday evening.

Some buildings, including the top of the CN Tower, were enveloped in fog on Saturday morning.

Residents urged to clear storm drains after rain

In a rainfall warning issued on Friday that was in place until early Saturday, the federal weather agency urged Toronto residents to clear storm drains from snow and ice to allow the precipitation to drain properly.

On Friday, the federal weather agency had said between 25 and 40 millimetres of rain had been expected overnight.

Trees in downtown Toronto were drenched with rain overnight. (Muriel Draaisma/CBC)

The Toronto and Area Conservation Authority says the heavy rain that drenched Toronto, combined with above freezing temperatures, could increase the potential for ice breakups this weekend.

Ice cover has been observed at the Humber River at Old Mill Road, Lower Don River, Etobicoke Creek at Marie Curtis Park, and Duffins Creek at Bayly Street in Ajax, the TRCA said.

All shorelines in the Greater Toronto Area should be considered hazardous and people are urged to be cautious around all bodies of water.

"All rivers within the GTA will experience higher flows and water levels, resulting in potential flooding and hazardous conditions, especially behind bridges and culverts where ice jams could be present," the TRCA said in its flood outlook for Toronto.

"Ponding may occur in low-lying areas. The combination of slippery and unstable banks could create hazardous conditions close to any river, stream or other water body."