Up to 100 mm of rain is expected to fall in the Lower Mainland

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The third atmospheric river in less than a week is expected to hit southern B.C. Tuesday, Environment Canada is warning, with strong winds and more flooding possible.

The region has already endured two atmospheric rivers in recent days, though officials have warned the third is expected to be the worst yet.

Environment Canada has issued a special weather statement ahead of the heavy rain, which is expected to arrive Tuesday and last through Wednesday. Between 50 to 100 millimetres is predicted to fall in parts of the Lower Mainland and winds gusting up to 60 km/h are also expected.

Some areas on Vancouver Island could see as much as 200 millimetres fall.

"Heavy downpours can cause water pooling on roads. Localized flooding in low-lying areas is possible," Environment Canada's alert warns. "Rising freezing levels and snowmelt may contribute to increased runoff."

Risk of increased flooding is already an issue, with flood warnings and watches already in place. As of Monday morning, the Tulameen, Coldwater and Lower Nicola rivers were under flood warning. A flood watch was in place for the Similkameen River.

The River Forecast Centre said in a statement Sunday night that significant rainfall impacting the Fraser Valley spilled over the Cascade and Coast mountains into Interior watersheds.

"Temperatures increased during the storm event and likely contributed to snowmelt at mid‐elevations and rain‐on‐snow runoff," the centre's summary of the current flooding situation says. "Rivers have risen quickly but are not expected to reach the levels from the Nov. 13 to 15 event, although they still may cause significant flooding."

But conditions could worsen in the days ahead.

"Currently, the weather models display significant uncertainty in total precipitation for the third event for the central region," the centre's flood summary says. "The risk remains for significant flooding under the wettest weather model scenario."

Late last week, Environment Canada issued an unprecedented "red alert" for parts of the province already devastated by the storm that saturated the ground earlier this month. 

"This alert, it's really due to the vulnerabilities that are on the ground, particularly in the Fraser Valley," Environment Canada's warning preparedness meteorologist Armel Castellan said last week, adding that the ground "is completely saturated."

"We hope that everybody is prepared, feeling ready, doing as much as they can in anticipation of this extraordinary set of storms that is affecting the South Coast."

- with files from CTV News Vancouver's Ian Holliday and Kendra Mangione -