Meteorologists call this type of rain pattern an “atmospheric river.” (News file photo)

Meteorologists call this type of rain pattern an “atmospheric river.” (News file photo)

‘Atmospheric river’ rainstorm headed for Fraser Valley, up to 70 mm expected

Heavy rains to start tonight until Thursday evening

A heavy rainstorm is expected to hit the Fraser Valley, bringing 50 to 70 millimetres of rain, according to a warning from Environment Canada.

Meteorologists call this type of rain pattern an “atmospheric river.” It’s caused by narrow regions in the atmosphere transporting water vapor outside the tropics. Once the vapor hits land, it releases in the form of rain or snow.

“These columns of vapor move with the weather, carrying an amount of water vapor roughly equivalent to the average flow of water at the mouth of the Mississippi River,” says the U.S. National Oceanic and Atmospheric Administration’s website. “Like rivers in the sky.”

The downpour start this evening will last until Thursday evening. It may cause flash floods, water pooling on roads as well as localized flooding in low-lying areas.

Environment Canada has put out a special weather statement for Metro Vancouver, which is expected to get close to 50 millimetres of rain.

Environment Canada weatherFraser Valley