Last month, we had doubled normal rainfall at SEATAC, but my rain gauge near Granite Falls recorded 3" more than SEATAC did. Is that really possible?
Yes...and it's because of our complex terrain. That's why rainfall varies greatly. 'Lifting' moist air up and over terrain increases rainfall, what meteorologists call orographic effects. We see that in our average annual rainfall. To offer a few examples, SEATAC averages 38", Arlington 46", Start Up 64" and Stampede Pass 100". Also showers, and local effects such as the Puget Sound Convergence Zone, can also produce locally intense rainfall...and significant variations over short distances.