So, you want to make a Seattle weather forecast in spring, eh?
Spring is one of the craziest weather months around Seattle as the battle between winter's lingering chill and summer's eventual warmth start to duke it out in the skies. April is especially true to the old adage: "Don't like the weather, just wait 20 minutes!"
And if you needed any proof, take a peek at this time lapse video from Skunk Bay near Hansville looking generally north/northeast. If you want closely, I think the clouds eventually come from each point on the compass as the winds swirl about through the day -- in fact, at a few points, there is really good wind shear where the low level clouds are moving almost exactly opposite to some of the mid-level clouds.
Also take a peek right around sunset toward the land in the upper right corner (Whidbey Island, toward Anacortes) -- you can see a big cumulus cloud explode off the terrain.
Anyway, sure illustrates just how difficult it can be mastering the weather around here when it can change so much: