Weather and Climate Patterns

The Temperate Rainforest is located in the cool, moist climate of the west coast of the North American continent - British Columbia, Canada; and Washington State and Oregon of the U.S.A. Natural, un-logged Temperate Rainforest are referred to as "old-growth" forests, since the trees are ancient that are over 500 years old and very large. These trees are primarily giant conifers - Sitka spruce, Western hemlock, Western red cedar and Douglas fir. There are always some younger trees in old growth forests as well.

A thick layer of fog rolls in over the British Columbia stretch of the Temperate Rainforest.

A Temperate Rainforest is defined as any forest between the Arctic Circle and the Tropic of Cancer or the Antarctic Circle and the Tropic of Capricorn that receives more than 50 to 60 in of rainfall a year and has a mild climate. In the Olympic National Park, an area that is part of the North American Temperate Rainforest biome, the annual rainfall exceeds this value; in fact, it receives around 140 to 167 in of rainfall annually. In a Temperate Rainforest, there are wet and dry seasons. During the 'dry' seasons, coastal fog supplies abundant moisture to the forest. While the climate of the Pacific Northwest varies considerably from Alaska to California, the presence of indicator trees in this biome, namely the Sitka spruce and Western Hemlock, indicates that climatically, the area is unified. The same mountains that trap the ocean moisture protect the area from severe weather extremes; therefore, there are not many storms in the Temperate Rainforest.

The temperature never freezes and never gets very hot in this biome. The winter temperatures rarely drop below freezing and summer temperatures are usually around 24 to 27C. The Temperate Rainforest experiences mild, wet winters and cool, foggy summers. The mild winters allow year-round growth of the conifers, while the foggy summers reduce the possibility of drought. The danger of drought is minimal in the areas of Alaska and Canada where precipitation is spread in a relatively even manner throughout the year. However, in southern California, drought becomes a more serious issue during the summer months. Western Washington, for example, receives only six to nine per cent of its annual rainfall during the summer months. The summer fogs that are typical of the coastal region provide several inches of moisture at a critical time, which allows for maximum growth of coniferous trees.