High Streamflow Advisory - Tulameen River and tributaries.

Flood Watch - South Coast, Lower Mainland, Lower Fraser Valley (UPGRADE)

High Streamflow Advisory – Coldwater/Nicola (NEW), Tulameen (NEW), Vancouver Island

Issued: 10:30 AM December 04, 2023

The River Forecast Centre is upgrading to a Flood Watch for:

• South Coast, including the Sunshine Coast, Howe Sound, North Shore Mountains
• Lower Mainland including Metro Vancouver
• Lower Fraser Valley, including up to Hope and the Coquihalla Summit, and neighboring basins

The River Forecast Centre is issuing or maintaining a High Streamflow Advisory for:

• Tulameen River and tributaries (NEW)
• Coldwater River and tributaries of the Nicola River downstream from Merritt, including Spius Creek (NEW)
• Vancouver Island

Weather Synopsis

An atmospheric river arrives to the South Coast of B.C. today. Heavy rainfall totals of 100 to 150 mm for West Vancouver Island, 100 mm for Inland Vancouver Island, 70 to 100 mm are forecast through the North Shore Mountains, 50 to 70 mm through the Fraser Valley, near 60 mm across the Coquihalla Summit to Merritt, and 40 to 60 mm through Manning Park are forecast today through tonight.

The storm system will bring a wave of warmer air, quickly elevating freezing levels and increasing the possibility of snow melt and rain-on-snow where snow has accumulated. On top of the forecast heavy rainfall, additional runoff inputs from rain-on-snow may be substantial.

River Conditions

River levels are expected to rise quickly beginning on Monday in areas receiving the brunt of the storm with flows peaking Tuesday into Wednesday. Current forecasting is suggesting that flows are expected to be highest for West Vancouver Island, the North Shore Mountains, and the Lower Fraser Valley, however this could shift into nearby areas if higher than forecasted rainfall occurs in other areas.

Uncertainty remains high about the specific storm track and rainfall amounts, as well as the significance of rain-on-snow inputs. Flows equivalent to 2-year to 5-year return periods are possible, with potential for higher ranges if higher end precipitation scenarios occur. Minor flooding in low-lying areas is expected, with the possibility of more extensive overbank flooding in areas experiencing substantial precipitation. Snowmelt and heavy runoff may cause pooling and localized flooding in areas with poor drainage (i.e., where stream channels and drainage structures are impacted by snow, ice, or debris).

The River Forecast Centre continues to monitor the conditions and will provide updates as conditions warrant.

Fast-flowing rivers pose increased risk to life safety. Be alert to road conditions, check DriveBC for current conditions, and do not drive through flooded areas. For information on how to prepare for flood hazards, visit PreparedBC.

A High Streamflow Advisory means that river levels are rising or expected to rise rapidly, but that no major flooding is expected. Fast-flowing bodies of water increase risk to life safety. 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.

Received from the BC River Forecast Centre, Ministry of Water, Land and Resource Stewardship