Weather Blog

Seattle and our 14,000 square mile umbrella

Seattle and our 14,000 square mile umbrella

Long-time Seattleites pride themselves on never needing an umbrella, but who needs one when Mother Nature provides it for free? In fact, Seattle is the beneficiary of a 14,000 square mile umbrella Wednesday called the Olympic Mountains.

The upper air flow is screaming at us from nearly due west, and as that air hits the western slopes of the Olympic Mountains, the air is forced upward where it condenses and, effectively, has its moisture wrung out like squeezing a sponge. Then, as the air crosses over the summits and sinks down the eastern slopes, it dries even further, leaving a large dry slot just to the east of the Olympics -- in our case, right over Seattle.

So while it's been dumping rain up in the mountains, Seattle's roads were relatively dry. And further west toward the actual "umbrella", the sun has even been peeking out!

Check out this brief video from Dr. Dale Ireland's web camera in Silverdale:

And here is the visible satellite image -- note the clearing over the western Kitsap Peninsula (and the huge rain shadow in Central Washington along the eastern slopes of the Cascades -- same physics involved.)

As of midday Wednesday, Olympia had 0.53" on Wednesday, and Everett and Sea-Tac Airport each had 0.14". But Seattle's Boeing Field in the heart of the rain shadow just had 0.02". (Meanwhile, Sequim, which usually enjoys the benefit of the rain shadow, has had 0.27" of rain.)

Need further proof? Let's take a tour of DOT cameras early Wednesday afternoon:

Here is the mostly dry Seattle-Shoreline area (note bare roads)

And here is the soggy scenes south, east and north in Tacoma, Issaquah and Everett, respectively:

By the way, look how well the forecast model nailed the rain shadow:

So don't let the lack of rain fool you in Seattle. It is really raining in the mountains!

And it's also raining in Bellingham -- apparently too much for Lou Nicksic who was inspired to produce this "the glass is half empty but the bird bath is always full" commentary on Western Washington weather :)