Terrain of the Pacific Northwest

If you have enjoyed hiking or driving anywhere in our region you know that there are a lot of interesting ups and downs, turns and twists. These land and water features serve to channel winds and influence storm development.

Following are some highlights of this beautiful region that are important to understanding our weather.

To start, what are the names the mountain ranges in B.C. and Washington? What are the names of the rivers and other bodies of water?

Where is the boundary between Canada and the United States? Some interesting features and history of this boundary can be found here.

In British Columbia, which is the province of Canada directly north of Washington, there are two main mountain ranges. The Canadian Coastal Range is a range of mountains running from northwest to southeast right on the west coast of British Columbia (55N 130W to 50N 123W). The Rockies run from northwest to southeast along the Alberta border (55N 123W to 49N 114W).

Along the Canada - United States boarder there is another area of mountains called the Okanogan Highlands (between 48N and 52N) that runs from the Canadian Coastal Range to the Rockies. The Fraser River, the largest river in B.C., cuts through the interior of B.C. to the Pacific Ocean. The mighty Fraser River meets the ocean at 49N 123W just south of the city of Vancouver.

In Washington, the Cascade Range runs north to south from 49N 122W to 42N 123W. The Coastal Range runs along the coast from 43N 124W to 47N 124W, ending in the north with the Olympic mountains on the Olympic Peninsula in Washington. The Columbia River cuts through both the Cascades and the Coast Range at the Washington - Oregon boarder.

There is a gap in the Coastal Range at 47N called the Chehalis Gap where the Chehalis River runs into the Pacific. The waterway connecting Puget Sound to the Ocean is called the Strait of Juan de Fuca. It runs north of the Olympic Mountains and south of Vancouver Island.

Identify the features described above on this terrain map of the Pacific Northwest and this terrain map of Western Washington.

Terrain and Snow

The terrain that affects snow events in Puget Sound in mainly the mountains in British Columbia and the Fraser river. Cold arctic air forms over the Yukon in the winter. This air is dense, and thus has a higher pressure than the surrounding air. Occasionally the air move south and is trapped in the "bowl" formed by the Canadian Coastal Range, the Rockies and the Okanogan Highlands.

Since the cold air has a higher pressure, and since air moves to lower pressure, the cold air will flow through gaps in the mountains. These gaps usually contain rivers. The gap that affects the Puget Sound is the Fraser River just across the border in Canada.

The cold air flows past Hope, B.C. and Bellingham Washington and into the Puget Sound region. During such an event, Bellingham will have a strong, cold wind out of the east or northeast.
Have you ever noticed that it is usually colder in the winter as you go into the mountains? Temperature usually decreases with height. Thus you may see some times when it is snowing in the mountains, but not in Puget Sound. The height at which the snow turns to rain is called the snow or freezing level. If the freezing level is at the ground, you get snow everywhere it is precipitating.

Sometimes the freezing level is almost at the ground. Then you can get snow on the tops of the hills in Seattle, like Capital Hill or Queen Anne hill, but not in the lower areas like Green Lake.

Sometimes other terrain features can affect the temperature and thus whether or not there is snow. For example, sometimes it will be raining in Ballard, which is near Puget Sound, but snowing in the University District. Can you figure out why?

During the winter, the water temperature is often warmer than the air temperature. Places near large bodies of water, like Ballard, can be a little warmer than other areas. If the temperature is near freezing, this can mean the difference between rain and snow.