Well, first let's document the warmth and sun of the interior. Here are temperatures at Seattle-Tacoma Airport for the past 12 weeks, with the average highs and lows noted for reference. Over half the days have had maximum temperatures above normal, with only a handful below normal. Only one day got to 90F. Heaven.
Perhaps a better way to see the story is the difference between the average maximum temperature from normal for the last two months. The coast is cooler than normal (green colors), while the rest of the state is warmer than average. So perhaps the coastal complainers have been on to something.
Much of the summer we have been stuck in the same boring pattern with high pressure offshore. Like this. Such patterns push cool, marine into the coastal zone, but are not strong enough to
We have also had a number of days with weak troughs offshore...enough to keep clouds in there and to promote thunderstorms over eastern Washington. But not strong enough to spread steady rain over the interior.
The pattern is now about to change, with the development of a stronger, persistent trough off our coast (see map for Friday at 5 PM). Showers along the coast, thunderstorms east of the Cascade crest, and lots of clouds for the rest of us. It couldn't last forever....