An atmospheric river pattern is developing along the Pacific Northwest, bringing several rounds of rain and wind to coastal British Columbia from Thursday, November 5, through the weekend and into next week.
Environment and Climate Change Canada’s forecast for Vancouver calls for showers on Thursday night, windy conditions and rain on Friday, followed by periods of rain over the weekend.
Vancouver is forecast to reach 13 C on Friday, while southeast winds could gust to 50 km/h near the Strait of Georgia overnight Thursday.
The immediate system is part of a broader Pacific storm track rather than a single one-day event.
A specialist outlook from the Center for Western Weather and Water Extremes says two atmospheric rivers are forecast to reach the Pacific Northwest between Thursday, November 5, and Sunday, November 8.
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What the atmospheric river forecast shows
The atmospheric river forecast points to repeated pulses of moisture rather than one continuous burst of extreme rain.
The first systems are expected to moisten soils and increase runoff before a potentially more impactful event develops during the following week.
The same outlook places a 60 to 80 per cent or higher probability of atmospheric river activity somewhere between British Columbia and northern California from November 9 to November 14.
The exact track and intensity remain uncertain, meaning local rainfall totals and flood impacts may change as forecasts are updated.
For coastal communities, the current forecast is expected to mean wet and windy travel conditions, reduced visibility and periods of heavy rain.
Higher elevations may see snow, although mild temperatures along the coast will keep much of the precipitation as rain.
Rain and wind expected across coastal B.C.
Environment Canada’s extended forecast shows a wet pattern across much of southwestern British Columbia.
Powell River is forecast to see rain Friday, periods of rain Saturday and continued rain or showers through Tuesday, November 10, according to the extended forecast.
Forecasts for parts of the Fraser Canyon, Okanagan Valley and Similkameen also call for showers, rain and windy conditions between Friday and Tuesday.
The Fraser Canyon forecast includes periods of rain Friday and Saturday night, followed by additional rain early next week.
The weather pattern may also bring snow to mountain passes and alpine areas.
Snow levels can rise and fall quickly during atmospheric river events, depending on the temperature and the position of each frontal band.
Flood risk remains dependent on rainfall totals
British Columbia’s River Forecast Centre had no flood warnings or advisories listed as active when the forecast was checked.
That means the developing storm pattern should not be interpreted as a province-wide flood warning.
Flood risk can nevertheless increase when several rainfall pulses arrive close together.
Saturated ground, rising snow levels, blocked drainage and strong winds can all contribute to localized problems, including ponding, debris flows, creek rises and travel disruptions.
The River Forecast Centre says it monitors streamflow, assesses flood risk and issues advisories or warnings when conditions warrant.
Its forecasting tools include short-range streamflow models for coastal and interior rivers, as outlined in the provincial guidance.
What residents should watch next
The most important forecast changes will involve the location of the strongest moisture plume, the duration of each rainfall period and snow levels in the mountains.
- Environment Canada rainfall, wind and special-weather alerts.
- River Forecast Centre advisories for rising rivers and streams.
- Highway and ferry updates during periods of heavy rain and wind.
- Local emergency notifications for flooding, debris flows or evacuations.
Residents in low-lying areas should keep storm drains clear where it is safe to do so, secure loose outdoor items and avoid driving through water covering a road.
Conditions can deteriorate quickly near creeks, steep slopes and areas with a history of drainage or landslide problems.
Forecast confidence is higher for a wet and unsettled stretch along the B.C. coast than for the precise timing or severity of the strongest atmospheric river later in the week of November 9.
Officials are expected to refine rainfall and wind forecasts as the systems move closer to the coast.
For background, CTCNews.ca previously reported on a major atmospheric river that brought heavy rainfall and flood risks to parts of British Columbia.
Frequently Asked Questions
What is an atmospheric river?
An atmospheric river is a long, narrow corridor of concentrated water vapour that can transport large amounts of moisture into a region and produce prolonged rain or mountain snow.
When will the atmospheric river affect British Columbia?
The first systems are forecast to affect the Pacific Northwest between November 5 and November 8, with additional atmospheric river activity possible between November 9 and November 14.
Is British Columbia under a flood warning?
The B.C. River Forecast Centre had no flood warnings or advisories listed as active when this forecast was checked. Local alerts can change as rainfall forecasts are updated.
Which parts of B.C. are expected to receive the most rain?
Coastal British Columbia, Vancouver Island, the Lower Mainland and parts of the Fraser Canyon are expected to see repeated periods of rain, while mountain areas may receive snow.
What should residents do before the stormy weather arrives?
Residents should monitor official weather and river alerts, secure loose items, keep drainage areas clear where safe and avoid driving through flooded roads or around washouts.
Fact-Checked: Key forecast details, atmospheric river timing and flood-advisory status were checked against Environment Canada, the B.C. River Forecast Centre and official atmospheric-river outlooks.
Disclaimer: Forecast timing, rainfall amounts and local impacts may change as new weather and river data become available.