My lawn (SE Washington state) looks similar. I use a company to manage my lawn treatments. I had them come out and they said the lawn is suffering from a fungus and needs a fungicide treatment and reseeding. I am hoping that helps.
Yup, that was my thought.
I’ve got a similar thing going on. I now have brown patches of various sizes all over the entire lawn. Between the hot, humid weather, excessive rainfall, and my failing to cut back the old manual watering schedule, my lawn is riddled with fungus.
Here’s what I’ve learned I’ll have to do to fix it:
- Two fungicide treatments, three weeks apart
- Fertilize (can do that at any time)
In late summer, early fall:
- De-thatch (I’ll rent a machine and do that myself)
- Aerate (I’ll hire somebody to do that)
- Patch the larger areas and over-seed the entire lawn
What a PITA 
I just went through all this two years ago to rid the lawn of weeds and bent grass. It had been looking so good, too.
I have to do that every year here in the Carolinas. Started 5 or do years ago doing this, and as long as the fungicide goes down early enough (before everything gets really bad), the lawn looks good.
I don’t usually have this problem. In fact: This season is the first time it’s ever happened in the thirty years we’ve been here.