After a record-hot and dry summer/autumn, storm season has finally arrived to the Pacific Northwest. A moderate cold front on Friday brought the first measurable rain of October to Western Washington, and on Saturday, a persistent Puget Sound Convergence Zone formed over the Seattle area. With a total of 0.72 inches of rain at Sea-Tac, Friday and Saturday were wetter than the previous 124 days combined at Sea-Tac airport, where only 0.54″ fell.
Much more rain, wind, and mountain snow is on the way. The jet stream will be aimed directly at the Pacific Northwest for at least the next 10 days as we continue to settle into our typical wintertime regime, bringing a parade of strong autumn storms into our area. The phrase “storm train” is often used to describe this type of pattern, but I don’t know if I’ve ever seen a storm train more threatening than this one!
Credit: University of Washington
Take a look at the rainfall forecast from the Euro model for the next 10 days. 2-3″ in the lowlands, with up to 10″ in the mountains. Great news for salmon, who have been waiting for the autumn rains before they begin their migration upstream to spawn.
There will be plenty of mountain snow as well, not only for the Cascades but for much of the Intermountain West. Stevens Pass and Crystal Mountain have already seen some snowflakes over the past few days, and Snoqualmie Pass may start seeing some flakes by the first week of November.
With the relatively low snow levels and low river levels, flooding is not a concern over the next 10 days. Even for the exceptionally flood-prone Skokomish River, flows are forecast to be well-below action stage.
Credit: National Weather Service
Autumn is a time of change for the Pacific Northwest, but I can’t remember a swifter change in the weather than this autumn. During the autumn, the North Pacific High, a semi-permanent area of high pressure that keeps the West Coast of the U.S. warm and dry in the summer, begins to weaken, and the Aleutian Low, a semi-permanent area of low pressure near the Aleutian Islands that helps steer storms towards the Western U.S., begins to strengthen. The switch from warm and dry weather to wet and cool weather typically takes place over the span of a month or more. This year, it occurred in a single week.
There are no signs of any dry weather or a warmup for at least the next 10 days of November. In the meantime, enjoy the rain and keep warm.
Charlie
