Flood warnings as potent Pineapple Express rains reach B.C.
Prepare for flooding in vulnerable areas as another potent atmospheric river washes into British Columbia to start the new week
A robust atmospheric river washing into the West Coast has revived the risk for flooding throughout southwestern British Columbia this week.
Several days of heavy rainfall are in the forecast for most areas, with heavy amounts already accumulated, exacerbating the flooding on waterways already swollen by the recent precipitation.
Gusty winds will also pose the risk for power outages and travel disruptions.
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Pineapple express brings hefty rainfall totals
This latest event is a particularly robust type of atmospheric river known as a pineapple express, as the plume of moisture originated in tropical latitudes around Hawaii where they grow pineapples.
Rainfall totals through Monday morning:
Effingham: 208 mm
Squamish: 162 mm
Port Mellon: 93 mm
Port Alberni: 88 mm
Coquitlam: 83 mm
Pemberton: 63 mm
Whistler: 52 mm
West Vancouver: 51 mm
Hope: 43 mm
Cultus Lake: 39 mm
WATCH: North Vancouver on flood alert as Seymour River swells
What's to come still
Folks throughout southern B.C. can expect two pulses of heavy rainfall: one throughout the day on Monday, with an additional round again on Tuesday.
This will be a high-impact weather event with additional flooding likely. Waterways are already swollen from the region’s recent atmospheric river events.
Flood warnings are in effect for the Sumas River and Chilliwack River, as well as the North Shore Mountains. Flood watches are in place for the Lower Fraser tributaries, as well as the Kingcome River and Englishman River. High streamflow advisories are in effect across the B.C. Coast, Vancouver Island, and Haida Gwaii.
The heaviest rainfall rates will arrive early Monday, with rates as high as 10-15 mm per hour possible. Rumbles of thunder are possible during this period.
Snowmelt from rising freezing levels will also contribute to runoff, further exacerbating the flood risk on Monday.
We’re on track to see storm totals of 80-100+ mm in the Fraser Valley and Coast Mountains through Monday. The highest amounts across lower elevations are forecast for the northeast sections of Metro Vancouver.
Locally, more than 200 mm of rain is possible in the North Shore mountains and western Vancouver Island.
A second round of moisture on Tuesday will bring additional rainfall, but not as much as we’ll have seen on Monday. This round will see cold air aloft produce heavy alpine snow, which will reduce the amount of runoff.
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In addition, avalanche risks are elevated. Travel in avalanche terrain is not advised in the coming days.
Wind threat builds with potential power outages
Gusty winds and saturated soils will increase the risk for tree damage and power outages through Monday evening. Delays and cancellations are possible for both ferries and flights across the region.
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We’ll see winds out of the southwest up to 80 km/h across Greater Victoria through Monday afternoon, increasing the risk for wind-related impacts in this area.
Strong winds will continue and push inland toward the Fraser Valley through Monday afternoon and evening, with local southwesterly gusts up to 90 km/h possible. As the low lifts into Alberta, damaging wind gusts up to 80 km/h will also be possible in the southern Interior.
A break in the storm parade by late December?
Temperatures will return closer to seasonal values starting Tuesday and are expected to persist through Christmas. This pattern may bring much-needed snowfall to ski areas while impacting travel through mountain passes.
Toward late December, a pause in the active weather pattern is possible if the storm track shifts farther south of the border temporarily.