Cold air will be shifting south through British Columbia over the weekend. A weather system on Sunday will arrive as cold Fraser outflow develops. Precipitation should change to snow around Whatcom county and the San Juans on Sunday. Cold wind chill will develop and blowing snow with poor visibility will be possible into early next week in the Bellingham area and San Juans.
The cold air will spread south through the rest of Western Washington Sunday night.
The leading edge of this cold air is called a modified arctic front. It is not unusual for snow to fall with this type of cold front as it moves south down the I-5 corridor. Snow amounts tend to be light with modified arctic fronts but falling temperatures can lead to icy roads after even light snowfall.
Another area that can see enhanced snowfall during Fraser outflow is around Port Angeles and along the Strait of Juan de Fuca. Cold air picks up moisture as it crosses the northern inland waters and snow falls in the northerly flow as it pushes into the north portion of the Olympics.
Areas along the coast and across Southwest Washington will not avoid the cold snap developing early next week. A weather system moving into Oregon on Monday could affect southwest Washington.