British Columbia’s River Forecast Centre issued an upgrade flood warning for the Squamish River and tributaries including the Cheakamus River on Monday, as another torrent of heavy rain was expected across the province’s South Coast.
A bulletin at 5:15 p.m. Monday said water levels in the Squamish River were rising, with flows reaching somewhere between a two- and five-year return period at a gauge near Brackendale, a neighbourhood north of downtown Squamish, B.C.
With additional rainfall expected in the river’s headwaters, the water levels may continue rising into Tuesday, it said.
Tributaries including the Cheakamus River were also “expected to exceed bank-full flow,” the bulletin said.
The forecast centre has maintained flood watches for the rest of the province’s South Coast, spanning all of Vancouver Island, the Sunshine Coast, the North Shore mountains and parts of the Fraser Valley, including the Sumas River.
Lower-level streamflow advisories are in effect for the Central and North coasts.
River levels were expected to peak in most areas on Monday and Tuesday.
The River Forecast Centre said the “potent” storms had delivered between 80 and 300 millimetres of rain through most of the region since Friday.
Alyssa Charbonneau, a meteorologist with Environment Canada, said Monday that warm air accompanying the series of atmospheric rivers saturating the region is raising the risk of flooding by melting snow in the mountains, causing runoff.
Charbonneau said there may be some breaks in the heaviest rains, but the concerns over flooding come from the “cumulative event” and its extended duration.
The weather office maintained a rainfall warning on Monday covering Squamish, Whistler and other communities near Howe Sound, saying another 60 to100 mm was forecast before the rain eases to light showers Tuesday morning.
Charbonneau said the rain is expected to persist until sometime in the middle of the week, perhaps Wednesday night, before easing up.
“We do see things cooling down toward seasonal, and it does look like we’re going to have a stretch of dry weather through the weekend,” she said.
Still, she cautioned, the longer-term forecast for B.C.’s South Coast should be taken “with a grain of salt” at this time of year because it can change quickly.
The latest Avalanche Canada forecast, meanwhile, shows the danger rating remains “high” throughout the south Chilcotin and Pacific mountain ranges, including alpine areas around Squamish, Whistler, Pemberton and Garibaldi Provincial Park.
The avalanche risk is also ranked as “high” in northwestern B.C., including mountains surrounding the communities of Prince Rupert, Terrace and Kitimat.
A bulletin from the forecaster says heavy rains have saturated and weakened the upper snowpack, and conditions weren’t expected to improve today.
Environment Canada says the latest heavy rains were expected to ease to showers this morning, but the wet weather will continue over the next few days.
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