Metro Vancouver officials are warning that heavy rains over the last 24 hours could lead to cloudy drinking water after a huge storm transformed the South Coast of B.C. into a slushy mess overnight Sunday.

A stranded driver on the Willingdon on-ramp to Highway 1 waits for rescue.
(CBC)

Heavy rain has been pelting the North Shore mountains where Metro Vancouver's water supply originates, which could mean more debris getting into the water.

Officials at the regional district are warning people with compromised immune systems — such as those with HIV or those undergoing chemotherapy — to boil their drinking water.

Other people may also want to stockpile water before the increased turbidity reaches homes, but so far a general boil-water advisory has not been issued.

Last year, one million people in the Metro Vancouver area were without safe tap water for 12 days after a massive storm unleashed landslides in the region's watersheds.

Officials denied allegations that years of clearcut logging on the steep slopes of the watersheds was connected to the landslides.

Flood watch on South Coast

Meanwhile, with 40 to 140 millimetres of rain expected by Monday night, the combination of heavy rain and melting snow prompted government officials to issue a flood watch for Greater Vancouver, South and Central Vancouver Island, Howe Sound and the Lower Fraser valley.

By noon Monday, the heavy rain and melting snow were already causing flooding in parts of Surrey.

Rob Costanza of the city's engineering department told CBC News that so far, 60 to 80 mm of rain had fallen on top of the snow from this weekend. He said parts of Bridgeview, Cloverdale and Newton were experiencing some flooding.

"We're anticipating more flooding as the day progresses. Our high flood level is going to peak at 5 p.m. this afternoon so that combined with melting snow and rain, we're definitely expecting more flooding."

Drivers on Willingdon Ave. in Burnaby hit some deep puddles Monday morning.
(CBC)

Costanza said crews spent Monday morning handling calls from homeowners to clear downed trees and blocked catch basins.

Environment Canada's Alyssa Charbonneau said Monday morning that the rain that started Sunday night will continue through Monday night, as the weather system won't move beyond the South Coast until late Tuesday. But there is sunshine in the forecast beginning Thursday.

More than 40,000 BC Hydro customers lost power overnight as high winds blasted Vancouver Island and the South Coast from Victoria to Hope, while heavy rain washed away the five to 50 centimetres of snow that fell Saturday and Sunday.

The largest power outages were in Courtenay, Comox, Campbell River, Cowichan Valley, the Southern Gulf Islands and across the Fraser Valley. According to the BC Hydro website, power was expected to be restored Monday afternoon.

Schools were reporting closures in Campbell River, the Southern Gulf Islands, Cowichan Valley, Nanaimo-Ladysmith, Comox Valley and the Malaspina University College at its Nanaimo and Parksville campuses.

West Vancouver police were asking drivers to avoid the Sea-to-Sky Highway because of deep puddles between Horseshoe Bay and Lion's Bay.

Interior highways coated

Even though winter does not begin until Dec. 22, the Eastern Fraser Valley and the Interior were getting a prolonged blast of the winter weather, with freezing rain and as much as 60 cm of snow at higher elevations predicted for the Southern Interior.

Traffic was slow along most of Vancouver's streets on the weekend because of slippy road conditions thanks to the white stuff.
(CBC)

The colder temperatures in the Eastern Fraser made roads icy, and public schools from Agassiz to Boston Bar were reporting closures.

Travel east of Vancouver was treacherous, with the Trans-Canada Highway closed from Hope to Jackass Mountain and from Jackass Mountain to Spences Bridge because of a high avalanche hazard. Most other Interior routes were reporting compact snow.

The Coquihalla Highway remained open, but there was compact snow and limited visibility, although temperatures were expected to climb later Monday.

Avalanche danger high

The warm front that brought the rain also brought unstable conditions to B.C's backcountry, prompting the Canadian Avalanche Centre to issue a warning to snowmobilers and skiers.

The storm crossed the South Coast on Monday morning, dumping rain and snow across the southern regions of B.C.
(Environment Canada)

Ken Bibby, a forecaster with the centre, said the avalanche hazard across much of the province is high.
 
"We're seeing 40 to 80 cm of storm snow that overlies a very weak layer that was buried [in] late November, and this layer was more or less widespread across the province," said Bibby.

"That's generally enough snow to be cautious in the backcountry, and you can expect natural avalanches on that in the short term," he said.