2005/01/19 Pacific Northwest soaked with "Tropical Punch"

Wednesday, January 19, 2005

As much as 200 mm (8") of rain have been recorded in portions of British Columbia, on the west coast of Canada since Monday. Even by "wet coast" standards, this is heavy rain.

The heavy and sustained precipitation across the lower mainland regions have caused mudslides and flooding, with roads and highways being closed and families evacuated. In Port Coquitlam, a retaining wall burst, throwing concrete and rubble tens of metres and covering an arterial road with mud to a depth of two metres.

Further inland and north, where colder temperatures have prevailed, the precipitation has been falling as freezing rain and sleet, or heavy snowfalls. Terrace, BC, was isolated as highways north and south of the city were closed due to a heavy glaze of ice. The Trans-Canada Highway and most other roads through the mountains were closed due to heavy and sudden snow accumulations which created severe avalanche hazards.

"The avalanche danger is at high or extreme in all of our six forecast areas," according to John Kelly at the Canadian Avalanche Centre in Revelstoke.

But these are only first hazards. "If the rain continues at the same magnitude and according to the forecast, then some of the rivers could reach flood stage either later [Tuesday] or Wednesday morning," said Allan Chapman, a hydrologist with the River Forecast Centre in Victoria.

The source of the wet weather is a large system reaching the coast from the Pacific Ocean tropics, a type of system nicknamed by meteorologists a "Tropical Punch". A similar system caused severe flooding and precipitation in 2003.

The system is not going away, either. Environment Canada expects the system, which lies southwest of Vancouver Island, to continue to develop "waves" of weather which will strike the mainland and head inland over the next several days to a week, possibly dropping 50-100 mm (2"-4") of additional rain per day at least until the end of the weekend.