The Fraser Valley is a geographical region in southwestern British Columbia, Canada, and northwestern Washington State. It starts just west of Hope in a narrow valley encompassing the Fraser River and ends at the Pacific Ocean stretching from the North Shore Mountains, opposite the city of Vancouver BC, to just south of Bellingham, Washington.
In casual usage, it typically describes the Fraser River basin downstream of the Fraser Canyon. The term is sometimes used outside British Columbia to refer to the entire Fraser River sections including the Fraser Canyon and up from there to its headwaters, but in general British Columbian usage, the term refers to the stretch of Lower Mainland west of the Coquihalla River mouth at the inland town of Hope, and includes all of the Canadian portion of the Fraser Lowland as well as the valleys and upland areas flanking it. It is divided into the Upper Fraser Valley and Lower Fraser Valley by the Vedder River mouth at the eastern foothills of Sumas Mountain, although the Lower Valley section upstream of McMillan Island and the Salmon River mouth (at Fort Langley) used to be called the Central Fraser Valley up until 1995 (see Central Fraser Valley Regional District).
In winter, the Fraser Valley occasionally plays a significant role in the weather regime along the west coast of North America as far south as California, acting as a natural outlet for the intensely cold Arctic air mass which typically sits over Western Canada during winter. Under certain meteorological conditions, strong winds pour out of the Fraser Valley and over the relatively warmer waters of the Strait of Georgia and the Strait of Juan de Fuca. This can cause ocean-effect snow, especially between Port Angeles and Sequim, where the air mass collides with the Olympic Mountains.[1] The cold air from the Fraser Valley can also flow out over the Pacific Ocean. Lanes of convective ocean-effect clouds and showers are produced as heat and moisture modify the very dry, frigid air mass. These then typically organize as a low-pressure system that returns the showers to the coast south of Canada, often bringing snow to unusually low elevations.