Parts of B.C. to see extreme rainfall totals from dominant atmospheric river
A powerful, early-season atmospheric river is targeting the North Coast of British Columbia this week, with forecasts calling for a Category 5 –– the highest on the scale.
Even though fall just began, B.C.'s pattern will be more reflective of late season rather than just the start of it.
The potent setup will include multiple atmospheric rivers, including a potent, early-fall event that could rank as a Category 5, the highest on the ranking scale. Rainfall totals will be quite high through this week, leading to elevated concerns over flooding in some areas.
Visit our Complete Guide to Fall 2024 for an in depth look at the Fall Forecast, tips to plan for it and much more!
Courtesy of a plume of moisture from southeast Asia, rainfall accumulations up to 200 mm this week are possible for the harder-hit areas. In regions of the heaviest rain, landslides and power outages are threats while pooling and ponding of water on roadways are possible this week.
Monday through Wednesday:
Moisture from southeastern Asia is the source region for the developing atmospheric river, and anyone who has travelled to Japan during the summer months knows how oppressive the conditions are there.
Atmospheric rivers are, for the most part, what you might imagine from the name — rivers in the sky. They’re long, narrow bands in the atmosphere that carry large amounts of water vapour, usually from the tropics where water and atmospheric moisture are abundant.
This next AR is forecast to bring heavy rain to northern and central areas of the coast. This particular AR will be stronger than the previous event, but it will track a bit farther north.
Upwards to 200 mm of rain is expected for the northern coast and Haida Gwaii; with lesser amounts for Bella Bella and Bella Coola compared to the weekend system. It’s a 48-hour affair as the stream of moisture stalls across the north, thanks to a stubborn ridge of high pressure situated across southern B.C.
Heavier rain is forecast for Prince Rupert as the trajectory shifts north, likely dumping more than 100 mm of rainfall on the community.
High pressure protects the Lower Mainland and southern Vancouver Island once again until the very end of the atmospheric river. It will brings periods of rainfall on Wednesday and more unsettled weather into Thursday as the storm track slumps south.
In regions of the heaviest rain, landslides and power outages are threats while pooling and ponding of water on roadways are possible this week.
SEE ALSO: Atmospheric Rivers: Expert explains the good and bad of these extreme storms
Forest fire burn scars give a heightened sensitivity to flooding impacts, increasing the threat of soil failure and impacts.
Thursday through Friday:
The active pattern brings another system to coastal B.C. late this week, with higher confidence of the storm track shifting towards the South Coast, bringing a period of unsettled and potentially stormy weather.
This storm will feature a deeper area of low pressure, increasing the threat of strong winds along the immediate coastline of the province.
Overall, however, a drier-than-normal pattern will dominate for the South Coast region through the end of September and into the beginning of October, as well.
The wettest city in Canada is Prince Rupert, B.C., which averages more than 2,500 mm of yearly precipitation. British Columbia is a province of weather extremes. Just 800 kilometres southeast of Prince Rupert is Canada’s driest city, Kamloops, which averages under 300 mm of precipitation annually.
In other words, it takes Kamloops roughly eight years to accumulate what Prince Report records in a single year.
Prince Rupert’s wettest September on record occurred back in 1908, tallying 517 mm, while the driest September on record was 1929, amassing just 26.4 mm.