British Columbia’s varied topography makes for radically varying temperatures, which rise or fall with changes in elevation, latitude, slope aspect, and distance from the ocean. The coastal region boasts the mildest climate in all of Canada, but this comes with one drawback: It rains a lot. The two main cities, Vancouver and Victoria, lie within this zone. Most of the interior is influenced by both continental and maritime air, resulting in colder, relatively dry winters and hot, dry summers. And the northern latitudes are influenced by polar continental and arctic air masses, making for extremely cold, snowy winters and short, cool, wet summers.
Precipitation in British Columbia is strongly influenced by the lay of the land and the waft of the wind, resulting in an astonishing variation in rainfall from place to place. For example, Lillooet, in the sheltered Fraser River Valley, is Canada’s driest community, whereas Port Renfrew on Vancouver Island’s west coast averages 4,000 millimeters (157 inches) of precipitation annually.
The amount of precipitation any given area receives is greatly determined by its location on the windward or lee side of the major mountain ranges—the windward side usually cops most of the downpour. Hence, the western side of the Coast Range is wet, the Interior Plateau on the east side of the Coast Range is relatively dry, and the western, windward side of the Rockies along the Alberta border is once again wet.
© Andrew Hempstead, from Moon Western Canada, 3rd Edition