As of 12:30pm, Thursday, November 25, the River Forecast Centre is upgrading to a Flood Watch for the Sea-to-Sky including areas around Squamish, Whistler and Pemberton.
The public is advised stay clear of fast-flowing rivers and potentially unstable riverbanks during the high-streamflow period.
The first of a series of storms has arrived on the South Coast. The storm is bringing heavy rainfall, with rainfall totals forecast to range between 40-70mm over the Fraser Valley and 50-80mm over the North Shore Mountains and Howe Sound, with higher amounts possible over higher terrain.
A subsequent atmospheric river event is forecast for the weekend with precipitation arriving mid-day on Saturday. Rainfall totals are expected to be higher for the weekend event. Additionally, temperatures will be warmer resulting in higher freezing levels. There is a greater risk for a rain-on-snow event to melt much of the current snowpack, adding additional water into rivers and creeks.
A third atmospheric river is forecast to reach British Columbia next Tuesday/Wednesday (Nov 30-Dec 1st). It is still too far into the future to provide exact details regarding the impacts and severity of this third storm.
Rivers are expected to see rises on Thursday in response to the first rainfall event, with the potential for highest flows (2-year to 5-year) expected around the Sunshine Coast, Howe Sound and North Shore corridor. Rivers in the Fraser Valley are expected to see rises, though currently these are expected to be more typical in magnitude for fall storms, however these may be more problematic to flood response and recovery efforts and damaged infrastructure in the region.
The second system arriving over the weekend will likely be more problematic. It is currently forecast to have higher rainfall totals, warmer conditions resulting in additional snowmelt and will occur immediately after the current storm system. There is potential for flows to reach 10-year to 50-year levels (or higher)– likely occurring Sunday or Monday.
Details of the COFFEE and CLEVER Model forecasts can be found at: http://bcrfc.env.gov.bc.ca/fallfloods/map_coffee.html, and
http://bcrfc.env.gov.bc.ca/freshet/map_clever.html
The River Forecast Centre continues to monitor the conditions and will provide updates as conditions warrant.
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