Weather Blog

Wanna get away? Sequim had 69 more sunny days than Seattle

Wanna get away? Sequim had 69 more sunny days than Seattle
Blue skies open up amid a stormy day. Photo taken Sept. 26, 2011 from Victoria, B.C. looking southeast toward the Sequim area.

Sequim not only boasts that it is the driest city in Western Washington, with annual rainfall on par with Flagstaff, Arizona, but also one of the sunniest, thanks to its unique position inside the Olympic Rain Shadow.

Now, new research has added more credibility to the claim.

David Britton, who lives in Sequim, set out to prove just how much nicer the weather is up on the northern Olympic Peninsula than the dreary skies over Seattle and Puget Sound.

The National Weather Service doesn't have any official weather stations in Sequim, so he placed a sunlight sensor on his home weather station, and carefully calibrated it to match data tracked atop the University of Washington's Atmospheric Sciences building in Seattle.

He developed four categories of sky cover: A "Mostly sunny" day, a "partly sunny" day, a cloudy day and a "dreary day." Each was based on certain complex thresholds of measuring how long his sensor recorded sunshine.

For example, a "mostly sunny" day meant over half the day had more than 33% of the maximum solar radiation observed for that day of the year, and at least 22% of the day had at least 60% or more of the maximum amount. A "dreary" day meant most of the day recorded less that 50 Watts per meter squared of energy. (See, I told you: "complex")

The results were pretty dramatic:

Over the entire year from Sept. 1, 2010 to Aug. 31, 2011, Sequim "outshined" Seattle in every category. Sequim had 127 mostly sunny days and 127 partly cloudy days, while Seattle had 88 and 117, respectively.

On the other hand, Sequim just had 9 dreary days while Seattle had 23.

Overall, there were 69 days over that period when Sequim recorded either a mostly or partly sunny day while Seattle had a cloudy or dreary day. That's pretty amazing -- it's as if they get two extra months of sunshine! Britton called these days "Rain Shadow Days."

Britton points out that the greatest advantages came when people likely needed to find some sunshine the most: in the autumn and winter. Sequim had 20 sunny days between November through January, while Seattle had just 4. Meanwhile, Seattle "out drearied" Sequim 19-4.

And while Seattle was locked in the spring that wasn't, it wasn't quite so bad up north. Sequim had 29 mostly sunny days to Seattle's 16, and overall had 23 "rain shadow" days where Sequim was in the top two sun categories and Seattle was in the bottom two.

These numbers do make sense because the rain shadow occurs when we get strong southwest wind that comes off the Pacific Ocean and slams into the Olympic Mountains -- pretty much what happens with almost all our storms in autumn, winter and most of spring.

As the air is forced to rise up the southern slopes, the water is "wrung out" like a sponge -- that's why there are incredible rain forests on the southwestern side of the Olympics - they take the brunt of the Pacific Storms.

But once that air reaches the summit and sinks down the northern side of the Olympics, now an opposite, drying pattern occurs as sinking air causes air to dry. This process creates the rain shadow and Sequim is usually right in the heart of it.

The only time when the shadow takes a break is in the summer as the storms aren't around. This is where Seattle starts to exert some advantage because Seattle doesn't get the fog and clouds from the summertime marine pushes that Sequim gets from being closer to the coast.

But even this summer, there were a handful of rainy days that seemed to bypass Sequim. Britton counted five rain shadow days in June, seven in July, and even two in August and four in September! (Yes, even though Seattle had a very sunny, warm September -- there were still advantages in Sequim!)

Port Angeles also in the shadow

Britton also sought to see whether nearby Port Angeles was close enough to get a benefit from the shadow, so he enlisted the help of Peter Alexander and his math classes at Lincoln High School to track the data as well from their rooftop.

And it turned out, they were just about as sunny and Sequim.. All said and done, Sequim recorded 675 hours of sunshine while Port Angeles ad 659.

You can see more of Britton's excellent research, as well as the criteria he used to measure sunshine and categorize each day, at his website: OlympicRainShadow.com

And in case you missed it from my earlier blogs, here are two videos of the Rain Shadow in action:

And here is a link to a blog where my parents took a drive through the rain shadow.