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No. 2006:
Rain Shadow

John H. Lienhard presents guest aboyd [at] (Andrew Boyd)

Today, guest scientist Andrew Boyd stays dry. The University of Houston presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

The town of Sequim (pronounced skwim) lies just across Puget Sound from Seattle -- only a short ferry and car ride. Looking north toward Canada, it lies at the eastern foot of the Olympic Mountains, whose Pacific slopes are home to the only rainforests in the lower forty-eight Unites States.

To be called a rainforest, an area has to receive over a hundred inches of rain per year. In the Olympics, the heaviest rainfall is more than twice that -- over two-hundred inches. By comparison, Houston, Texas, and New York City each receive only about fifty inches, and both are pretty wet.

Sequim is only forty miles east of the wettest parts of the Olympic rainforest. Given its location, you might imagine that Sequim is a very wet place. Yet, remarkably, it receives only sixteen inches of rain annually - about the same as Los Angeles.

This amazing state of affairs is caused by the rain shadow effect of the mountains. During the winter months, strong, moist west winds blow in from the Pacific. The mountains deflect those winds upward from sea level to over seven thousand feet. They're cooled on the seventy-mile trip across the mountains; almost all the water they contain condenses out in the form of snow or rain. That's what causes the Olympic rain forests. Then the air, now wrung out and relatively dry -- makes its steep descent. Only after it passes over Sequim, does it begin taking on more water as it heads off toward Seattle. 

The result is what locals rightly call a "blue hole." It's not uncommon to find a patch of deep blue sky over the city, while the surrounding areas are covered in clouds. That hole in the sky is well-known to pilots who fly over Sequim.

Imagine walking in a straight line from Sequim into the rainforest. For every mile you traverse, the annual rainfall goes up about four and a half inches. It's actually not quite that bad, since the rainfall rises more slowly at the beginning of your walk and faster near the end. Still, the change is so severe that living even a few miles from Sequim can leave you a lot wetter -- as the Chamber of Commerce is all too happy to remind us.

Further flaunting the city's unique character, residents proudly celebrate the Sequim Irrigation Festival each year. It commemorates the opening of the first irrigation ditch in 1895. The land is simply too dry to grow anything without help from nearby streams and rivers. 

When you think about almost three-hundred days a year with at least some sunshine, you may be tempted to rush off and experience what may sound like Shangri La. But remember, while the average January temperature is a reasonable thirty-nine degrees, the average August temperature is a meager sixty-one degrees. And ocean temperatures hold at a steady fifty degrees throughout the year. All in all, it's a great place for hiking, biking, and partaking in delicious cold-water seafood. But, if you plan on water-skiing -- well, it'll be a good idea to bring your wetsuit. 

I'm Andy Boyd, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)

Dr. Andrew Boyd is Chief Scientist and Senior Vice President at PROS, a provider of provider of pricing and revenue optimization solutions. Dr. Boyd received his A.B. with Honors at Oberlin College with majors in Mathematics and Economics in 1981, and his Ph.D. in Operations Research from MIT in 1987. Prior to joining PROS, he enjoyed a successful ten year career as a university professor.

General information on Sequim can be found on the following web sites: and 
And for the Irrigation Festival, see: