Environment Canada has posted special weather statements advising that heavy rains are likely to pour down across a wide area including Victoria, Metro Vancouver, the Fraser Valley, the Sunshine Coast, Whistler, the Fraser Canyon, Quesnel, the Columbia region, the Kootenays and the Okanagan.
Thunderstorms may also be brewing for areas east of the Fraser Canyon.
Thunderstorm watches are in effect for areas including and east of the Boundary, Arrow Lakes and West Columbia regions. Environment Canada says that, in those regions, "conditions are favourable for the development of dangerous thunderstorms that may be capable of producing strong wind gusts, large hail and torrential rain."
Environment Canada recommends people stay indoors in those areas: "There isn't a place outside that is safe during a thunderstorm."
Parts of the Boundary, Kootenay, and Columbia regions may see 25 to 50 millimetres of rain falling in under a few hours this afternoon or early evening.
To the west, the heavy rain is most likely to hit later tonight.
"Some computer models are suggesting excessive rain that may trigger short-fuse rainfall warnings across the Lower Mainland and Southern Vancouver Island later today," Environment Canada said in the special weather statement.
In areas where localized flooding occurs, motorists are being warned that fast-moving water across a road can sweep vehicles away.
Environment Canada said in those parts of southeast B.C. that may see the heaviest showers, people should avoid rapidly-rising rivers and creeks, which can sweep away bridges, culverts, buildings, and people.