Today will be the last sunny, dry day for a long time. You can see the changes aloft as thin cirrus moves in aloft and contrails fill the sky. Contrails are a real sign of an approaching system since the air has to be close to saturation for them to form...the extra water vapor from combustion supplies the water needed to produce saturation and cloud droplets.
A weak front will approach tonight....and rain should start in the lowlands after midnight. The front should get through around breakfast time and then there will be a few hour break before the next...and stronger...frontal system moves in. Both of these fronts will bring considerable snow to the mountains. Colder air will move in behind the second front on Saturday night...and a few snow showers could reach the lowland hills on Sunday AM. But no big accumulation.
On Sunday, a low center will approach from the SW and this will bring more rain to the lowlands and snow to the mountains on Sunday afternoon. The low will bring strong winds to the northern Oregon coast and then breezy conditions over the Puget Sound lowlands on Sunday night.
The rest of the week remains cold and wet..with the mountains picking up lots of snow.