Temperatures are moderated at all times of the year by maritime air, particularly in winter. Winter precipitation is high. Low pressure areas and associated storms are steered into the area by the polar jet stream. Passage of the usually strongly occluded fronts is slowed by the mountains resulting in long duration but generally low intensity storms. Temperatures associated with these storms are often mild enough that rain falls at lower elevations of the forest while snow falls at higher elevations.
Summertime precipitation is usually low to nonexistent.
The North Pacific anticyclone intensifies and bulges to the northeast along the coast. This blocks the passage of cyclonic storms and stabilizes the air. It is notable for its very large winter precipitation which leads to significant soil water surpluses and implied runoff in this season. The runoff is not as large as implied in Table 2.2, however, because some of the precipitation especially at the higher elevations is in the form of snow. It is also noteworthy that a soil water deficit occurs during the summer of most years because of the low rainfall.