I do that too. Except I don't buy any grass seed, the lawn just comes back the next year. One pretty awesome thing about Seattle is that virtually no one waters their lawn in the summer. Brown lawns are standard.

In my semi-shady and shady areas, the grass will come back when the weather cools and it starts to rain. That's because the grass is dormant, not dead. In the sunny areas, it will also remain dormant if there are occasional summer rains. If we get a sustained hot, dry spell, the grass goes from dormant to dead. This was one of the best years so far for my lawn. I only needed to reseed two dead areas.

PSU