Weather Blog

How could Bremerton be 4" wetter than Everett?

How could Bremerton be 4" wetter than Everett?

What a difference a few miles makes. As of noon Friday in the heavy rain storm that hit the region this week, Bremerton had 5.34" of rain while Seattle (Sea-Tac Airport) was around 3" and just up the road a bit, Everett "only" had 1.33".

How is that possible? You can thank the Olympic Mountains and their rain shadow.

When moist air hits the southwest side of the Olympics, the air is forced upward where it condenses and the moisture gets squeezed out like a sponge. But on the flip side, when air sinks down the other side of the mountain, it dries out and loses some moisture.

This is how Sequim ended up being the driest place in Western Washington, with just 18" of rain per year -- they are in the heart of where the rain shadow typically lives.

Here's a chart of annual rainfall for Washington to show this effect:


In this storm, the flow has been orientated a bit more to the east, so the rain shadow is extended a bit more east and south of where it typically sets up shop.  That's why Port Angeles is well over 2" but Everett and Oak Harbor have yet to cross the two-inch threshold. Meanwhile, to the south and outside the shadow in Seattle, it's been much wetter.

Here is a radar shot from Friday morning showing the rain shadow in action.

..and here is a visible satellite image -- note the clearing spot on the northeastern side of the Olympics.

Note that the rain shadow doesn't mean it'll be dry there, many times, including this case, it makes the rain much lighter, as evidenced by the storm totals.

This also shows one of the great ironies of living in Snohomish County -- a day like today, they get less rain than everyone else.  But a day like Tuesday, they get absolutely poured on while the rest of the region is dry.  The Puget Sound Convergence Zone is the culprit there, and believe it or not, it just about perfectly counterbalances the rain shadow in that Everett gets, on average, the same amount of annual rainfall as Seattle. They might just accumulate the bulk of their rain on different dates.