A vigorous storm heading for B.C.'s South Coast has triggered a series of Environment Canada snow and rainfall warnings spanning from Vancouver Island to the Fraser Valley.

The weather agency is forecasting periods of heavy rain will drench much of the Lower Mainland Wednesday evening, with areas near the mountains expected to see up to 8 cm of rainfall before conditions taper to showers on Thursday night.

"This storm, because it's moving so slowly, it's going to deliver quite a bit more precipitation than your average winter storm," Environment Canada's Matt MacDonald told CTV News.

The weather agency predicted the Pacific frontal system would move southward from the central coast in the morning, then stall over the South Coast and Vancouver island.

Flash flooding, water pooling and landslides are possible.

The warning applies to Vancouver, Burnaby, New Westminster, Coquitlam, Maple Ridge, West Vancouver, North Vancouver, Chilliwack, Abbotsford and Hope.

On Burnaby Mountain, the precipitation fell as snow at one point on Wednesday afternoon.

The storm has also triggered a high streamflow advisory for several rivers and tributaries on the South Coast and Vancouver Island. Environment Canada said the Chilliwack River, Seymour River, Stewamus River and others are expected to surge late Wednesday.

"Things can change rapidly. By the time you come back on a hike, the trail could be gone and the banks are fairly saturated and unstable," the BC River Forecast Centre's Dave Campbell said.

The worst of the rain is expected to hit Vancouver Island, with "copious rainfall" in the forecast for some areas. The island's west coast could see more than 15 cm of rainfall, while other spots, including the area between Qualicum Beach and Fanny Bay, could see as much as 10 cm.

Elsewhere on the mainland, snowfall and dangerous driving conditions are the main concern. Environment Canada says the Sea to Sky Highway could see significant snow accumulations near Squamish and Whistler before the weather transitions to rain.

"The highway passes, I'd say, are going to get particularly ugly," MacDonald said.

Environment Canada warned the transition from heavy snow to heavy rain would begin near Squamish overnight and progress toward Whistler on Thursday.

It warned drivers to be prepared for quickly deteriorating conditions and rapidly accumulating snow.

There's more snow in the forecast on the eastern end of the Fraser Valley, particularly on the Coquihalla Highway from Hope to Merritt.

"There exists the potential for freezing rain over sections of the highway Thursday morning and early afternoon," Environment Canada said in a 4:45 a.m. warning. "Prepare for quickly changing and deteriorating travel conditions."

The weather agency said up to 35 cm of snow is expected to fall over the highway by late Thursday.  

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