The River Forecast Centre is issuing a High Streamflow Advisory for the South Coast including:
- Sea-to-Sky including areas around Squamish, Whistler and Pemberton
- Sunshine Coast
- Howe Sound
- North Shore Mountains
- Lower Mainland including areas along the Fraser Valley and areas around Hope
The River Forecast Centre is maintaining a Flood Warning for:
- Sumas River including Sumas Prairie and surround area
A prolonged period of active weather is expected throughout coastal BC over the coming week as several atmospheric rivers pass over the region. The first of these is expected to make landfall later on Wednesday, starting on the North Coast and Central Coast, and sliding southward into Thursday. This storm is expected to bring heavy rainfall, with rainfall totals in the 40-70mm range over the Fraser Valley and 50-80mm over the North Shore Mountains, and higher amounts possible over higher terrain.
Subsequent atmospheric river events are forecast on the weekend, starting up again later on Saturday. Additional storms are expected early next week. There is still considerable uncertainty over the locations and severity rainfall of the weekend and next week storm cycles, however the pattern of extremely active weather and heavy rainfall is expected throughout the advisory region.
Rivers are expected to see rises on Thursday in response to rainfall, 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.
Persistent periods of high flows are expected over the weekend and into next week. Additional information will be provided later in the week (Thursday and Friday) as weather and river forecasts see decreased uncertainty.
Flood levels on Sumas Prairie and on the Sumas River have been slowly receding. Additional rainfall on Wednesday to Friday is expected to provide modest additional runoff into affected areas and may slow the rate of the recession of water levels there. On the Nooksack River, the Northwest River Forecast Centre (NOAA) is currently forecasting the potential for the Nooksack River to reach overbank flood stage at Cedarville and Ferndale on Friday, with ongoing risks again later next week. At this time significant overflow from the Nooksack River into the Sumas River drainage is not expected, however is continuing to be monitored, as this scenario has the potential to emerge if higher than currently forecast rainfall occurs into the Nooksack River watershed.
- The public is advised to stay clear of the fast-flowing rivers and potentially unstable riverbanks during the high-streamflow period.
Details of the COFFEE and CLEVER Model forecasts can be found at:
- http://bcrfc.env.gov.bc.ca/fallfloods/map_coffee.html, and
The River Forecast Centre continues to monitor the conditions and will provide updates as conditions warrant.
- A High Streamflow Advisory means that river levels are rising or expected to rise rapidly, but that no major flooding is expected. Minor flooding in low-lying areas is possible.
- A Flood Watch means that river levels are rising and will approach or may exceed bankfull. Flooding of areas adjacent to affected rivers may occur.
- A Flood Warning means that river levels have exceeded bankfull or will exceed bankfull imminently, and that flooding of areas adjacent to the rivers affected will result.