Trick-or-treaters should get their umbrellas and ponchos ready for what is shaping up to be a wet Halloween night.

Environment Canada issued a special weather statement for the City of Toronto and parts of the GTA on Wednesday ahead of “potentially significant rainfall” that is expected to continue through Friday.

“A low pressure system will approach southern Ontario from the southwest. Rain is forecast to begin this morning and end Friday morning. Rainfall amounts of 30 to 50 mm are possible, with the heaviest rain occurring Thursday afternoon,” Environment Canada said in its weather advisory.

“Strong northwesterly to westerly wind gusts of 70 km/h are possible Thursday night into Friday morning.”

The rain began falling steadily in Toronto at around noon Wednesday amid a high of around 10 C.

The national weather agency is predicting 15 to 25 more millimetres of rainfall in Toronto on Thursday.

The daytime high on Thursday is expected to hit 13 C but the temperature will fall to 9 C in the afternoon.

While adverse weather conditions have prompted some cities to postpone trick-or-treating to another day, a spokesperson for Mayor John Tory said the city is “not messing with Halloween.”

“Mayor Tory hopes families across the city have a fun Halloween night and assures kids that their costumes are still great even if they have a coat on as well.” Spokesperson Don Peat said in an email.

“The City of Toronto reminds motorists daily of the need to be vigilant and look out for pedestrians, especially during inclement weather. We want young people – of all ages – to safely enjoy Halloween.”

TRCA urges caution around waterways

With heavy rainfall expected across the GTA, the Toronto and Region Conservation Authority is also calling on people to exercise caution around waterways.

“Due to the significant rainfall, all rivers within the GTA will be experiencing higher flows and water levels, resulting in potential flooding and hazardous conditions,” the TRCA said in a statement Wednesday. “The possibility exists for flooding on roadways and in low-lying areas. The combination of slippery and unstable banks could create hazardous conditions close to any river, stream or other water bodies. All rivers and streams within the GTA should be considered hazardous.”

The statement advised residents to keep children and pets away from slippery banks and waterways.

Barrie could see snow

For a scare worthy of Halloween, areas north of the GTA could see snow for the first time this season on Thursday night.

A special weather statement in effect for areas including Barrie, Collingwood, and Midland says residents in those areas could see some of the white stuff around the witching hour.

“As the low passes by Thursday night, rain may change over to snow before tapering off Friday. Snowfall amounts of 2 to 4 cm are possible, especially over higher ground inland from Georgian Bay,” Environment Canada said in its statement.

“There is uncertainty in the track of the low, which will affect how quickly the rain will change over to snow and subsequent snowfall amounts. Some folks may wake up to snow covered grass for the first time this season Friday morning.”

Snow aside, those areas are expected to see anywhere from 20 to 40 millimetres of rain by Thursday evening.