100 straight hours of rain: B.C.'s flood and avalanche risks raised
A strong-rated atmospheric river is bringing significant, prolonged rainfall to British Columbia, prompting flood alerts and raising the threat of avalanches
An unseasonable atmospheric river event is impacting British Columbia. It is bringing torrential rainfall, rising freezing levels and rapid snowmelt, leading to a significant risk of flooding and avalanches
A pineapple express is dousing the B.C. coast with significant rain and a freezing level spike through early Tuesday. It's unusual to have such a potent atmospheric river, which could rate as an AR3 or AR4 for the immediate coastline, for mid-March. Most of the affairs tend to happen in mid-fall and early winter.
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Some areas could see 50 mm to 400 mm of rain while other locales could see up to 100 consecutive hours of rain without a break.
Expect extensive water pooling on roads and washouts may occur, so there could be road closures and difficult travel with the rainfall.
Pineapple express expected through much of this week, flood alerts issued
The B.C. River Forecast Centre maintains a flood watch for:
Northern and western Vancouver Island
Central Coast
Near 200 mm of rainfall, especially near Bella Coola, Bella Bella, and the surrounding coastal areas.
Rising freezing levels and rain-on-snow runoff are likely at mid-elevations, rapidly increasing flow rates
A pineapple express is an atmospheric river that originates near Hawaii. This deep, rich plume of tropical moisture can fuel heavy rainfall and rising freezing levels across southwestern B.C.
There has been lots of lower-elevation snow in elevations 400-1200 metres over the past week, increasing run-off with snowmelt.
Given its strength and predicted longevity, forecasters anticipate this pineapple express event to rank an AR3 or AR4 along the immediate coastline, which means this type of event is often hazardous with river flooding impacts possible. Some areas could see the atmospheric river endure in two waves and persist for more than 72 hours.
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Some remote locations on western Vancouver Island and the North Shore Mountains will be subjected to up to 100 straight hours of rainfall this week. That’s more than four days of consecutive rainfall, highlighting the risk of flooding and rapid snowmelt.
This surge of moisture tracking northeast directly from Hawaii is fuelling heavy rainfall, which will continue for much of this week.
Rainfall forecast
Tofino/western Vancouver Island: 200-400 mm
North Shore Mountains: 150 mm-200+ mm
Squamish: 150 mm-200 mm
Campbell River/Comox Valley: Approximately 50 mm
Nanaimo: 50-75 mm
Victoria: 30-50 mm
Lower Mainland (south of Fraser River: 75 mm-100 mm)
North of Fraser: 100-200 mm
In addition to the heavy rainfall, we’ll also see freezing levels spike to more than 2000 metres on Monday, a rise that will last through the week before falling on Friday.
As a result, alpine rain is expected over the course of the week, leading to the elevated avalanche danger .
On Tuesday, the avalanche danger is forecast to remain high for the Coast Mountains, including high danger at or below the treeline.
The high avalanche danger will likely persist on Wednesday. The start of March featured cooler weather with significant alpine snow, which has begun to melt this week.
The combination of heavy rainfall and snowmelt will likely elevate flood alerts throughout the region during the days ahead.
Pay close attention to forecasts and alerts for your area in the coming days.
Stay with The Weather Network for all the latest on conditions across B.C.