The BC River Forecast Centre has issued a High Streamflow Advisory for Lillooet River near Pemberton (and tributaries).
A moderate atmospheric river event has arrived on the southern coast of British Columbia today. The event is expected to persist for nearly 48-hours and bring moderate to heavy precipitation throughout areas of south-west British Columbia. Environment and Climate Change Canada is forecasting 75-150 mm of total rainfall for most areas over the two-day period from Friday to Sunday. Higher rainfall amounts are possible, particularly over higher terrain, with the potential for localized amounts in the 150-250 mm range. Temperatures are expected to rise, with freezing levels forecast to peak around 2500 m by late Friday. Recent snow accumulation at elevation has occurred over the past few weeks, with 5-40 mm of snow water equivalent currently observed at automated snow weather stations throughout the region. Most of the snow on the ground is expected to melt during this event and will contribute additional runoff to rivers.
Rivers are expected to rise rapidly on Friday and into Saturday in response to rainfall, with peak flows expected on Saturday. Larger rivers, including the Squamish River, will likely experience peak flows on Sunday. Modelling is indicating the potential for flows in the 2-year to 5-year return period in most rivers through the region, and potentially higher depending on the rainfall rates and amounts that ultimately occur. The most recent COFFEE model results forecast potential flows at or greater than 20-year return period for rivers on the North Shore, Howe Sound and Sunshine Coast.
The storm system track is very narrow and could shift as the storm progresses; regional impacts could be more or less than currently forecast depending on where the heaviest rainfall actually occurs.
Details of the COFFEE and CLEVER Model forecasts can be found at:
The public is advised to stay clear of the fast-flowing rivers and potentially unstable riverbanks during the high-streamflow period.
The River Forecast Centre continues to monitor the conditions and will provide updates as conditions warrant.
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What does a High Streamflow Advisory mean?
River levels are rising or expected to rise rapidly, but that no major flooding is expected. Minor flooding in low-lying areas is possible.