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 Lower Mainland, close to 50 mm expected

Heavy rains to start tonight until Thursday eveining

Heavy rains are expected to hit the Lower Mainland, bringing close to 50 millimetres of rain, according to a special weather statement 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 Fraser Valley is expected to get 50 to 70 millimetres, and Environment Canada has put out a rainfall warning for the region.

It may be at risk of flash floods, water pooling on roads as well as localized flooding in low-lying areas.

Environment Canada weatherlowermainland