Why Is It So Dang Sunny

Pssst.. spoiler alert! It’s not the reason you think!

I noticed something when I moved to the city of Seattle. That it was in fact, not always rainy in summer but in fact quite sunny. When asking why I was told it was because of the convergence zones. But this is actually a misunderstanding. The Puget Sound Convergence Zone (PSCZ) or Seattle Convergence Zone actually doesn't make Seattle sunny in summer. In fact, it's a weather phenomenon that typically creates clouds and precipitation!

The Seattle Convergence Zone occurs when northwest winds split around the Olympic Mountains and then converge again over the Puget Sound region, typically somewhere between Seattle and Everett. When these air masses meet, they're forced upward, which creates:

1. Cloud formation

2. Increased precipitation

3. Sometimes thunderstorms in the convergence area

Seattle's sunny summer weather actually comes from a different weather pattern - the Pacific High pressure system that typically sets up off the coast in summer months. This high pressure system blocks storm systems and creates the characteristically dry, sunny weather that Seattle experiences from roughly July through September.

The convergence zone is most active in spring and fall, when the regional wind patterns are more conducive to its formation. It's one reason why some areas north of Seattle can receive significantly more rainfall than areas to the south or north of the convergence zone.