Flood warning issued for North Shore and Howe Sound as storms continue through the weekend

Successive storms have pushed rivers on BC's South Coast toward their banks, and the province's River Forecast Centre upgraded the region's status to a flood warning on Wednesday morning, covering the North Shore for the first time in this round of storms.

The River Forecast Centre issued the upgraded warning for the South Coast, covering Howe Sound, the Sea-to-Sky corridor and the North Shore, at 8:30 AM on Wednesday, November 11. A second flood warning for the Pemberton Valley was issued at 8:00 AM. The North Shore includes North Vancouver and West Vancouver, two municipalities that sit at the foot of steep mountain watersheds that drain quickly during heavy rain events.

What a flood warning means

The River Forecast Centre defines a flood warning as the stage at which river levels have already exceeded or will imminently exceed the top of the river banks, with flooding of nearby land as the result. This is a step above a flood watch, which signals that conditions are right for flooding but that it has not yet occurred. The centre upgrades a watch to a warning when the data shows that flooding is happening or is about to happen.

The North Shore and Howe Sound entered flood warning status Wednesday, moving up from the flood watch that had been in place for the South Coast since November 9. Flood watches remain in effect for Vancouver Island and the Central Coast region around Kingcome.

The storm pattern and what is forecast

Environment Canada meteorologist Michael Gismondi told Global News on Wednesday morning that there would be "a possible lull this morning before the rain is expected to re-intensify later." He said wet conditions are expected to continue into the weekend as part of a series of storm systems affecting the South Coast.

Environment Canada has an orange rainfall warning, its second-highest alert level, in place for Howe Sound and the Sea-to-Sky Highway corridor from Squamish to Whistler. The warning covers up to 160 millimetres of rain during this multi-day event and extends to Thursday morning. The warning notes that localized flooding is likely, some roads may become impassable, and landslides are possible on steep slopes.

Western and inland parts of Vancouver Island face even larger totals. Global News reported that rainfall amounts could top 250 millimetres there during this event, which Environment Canada also covers with an orange rainfall warning. The orange level indicates the high hazard rating Environment Canada assigns when heavy rain poses a risk to property and potentially to people.

Inland, Central BC is dealing with a separate hazard: a strong and slow-moving storm system bringing wind gusts of up to 100 kilometres per hour in some areas, according to Global News. Those winds were expected to ease Wednesday night.

Advisories elsewhere in the region

In addition to the flood warnings for the South Coast and Pemberton Valley, the River Forecast Centre issued high streamflow advisories for two other areas on November 10. The advisories cover Southern Vancouver Island and the combined area of the Fraser Valley, Fraser Canyon and Chilcotin. A high streamflow advisory sits below a flood watch in severity: it means river levels are elevated and require monitoring, but flooding has not yet been forecast.

This range of warnings and advisories, stretching from the South Coast across to Central BC, reflects a broad system rather than a single localized rainfall event. The River Forecast Centre tracks each watershed separately, and Wednesday's status means the rivers draining the North Shore and Howe Sound watersheds reached the threshold for the most serious category.

What to do if you are near the North Shore rivers

The flood warning covers land adjacent to rivers in the South Coast, including Howe Sound and the North Shore. The River Forecast Centre's definition states that flooding of areas adjacent to affected rivers will result. Residents who live near rivers or in low-lying areas of North Vancouver and West Vancouver should not wait for water to arrive before moving to higher ground if they have reason to believe their property is at risk.

The River Forecast Centre updates its warnings as conditions change throughout the day. Its warnings page at bcrfc.env.gov.bc.ca shows the current status for each region, including whether the South Coast warning has been extended, changed or lifted. The status can change several times during an active flood event as river levels respond to rainfall and as forecasters update their models.

Roads and travel

Road conditions related to flooding are updated on DriveBC at drivebc.ca. The Sea-to-Sky Highway, Highway 99, runs through the orange rainfall warning area between Squamish and Whistler and can be affected by slides or flooding during heavy rain events. Environment Canada's warning notes that some roads in the area may become impassable. Check DriveBC before travelling that route on Wednesday and Thursday.

Environment Canada's current alerts for the Vancouver area, including any changes to the orange rainfall warning, are at weather.gc.ca. The forecast calls for a brief reduction in rain intensity on Wednesday morning before the system returns, with the wet pattern continuing through the weekend. The River Forecast Centre's advisories for the Fraser Valley and Southern Vancouver Island remain in place and may also be upgraded if rainfall continues at forecast rates.