If your lawn gets thinner every year, with moss creeping in and puddles standing after every rain, the problem is usually below the grass. Clark County has a lot of clay soil, and months of wet weather and foot traffic compact it until roots can't get the air, water, and nutrients they need.
Core aeration fixes that by pulling thousands of small plugs of soil out of the lawn. The holes let water soak in instead of running off, give roots room to spread, and open a path for fertilizer to reach where it's needed. The plugs left on the surface break down on their own within a couple of weeks.
Dethatching is the other half. Thatch is the layer of dead grass and moss that builds up between the blades and the soil. A thin layer is fine, but once it gets thick it blocks water and smothers new growth. Raking it out before aerating gives the lawn a clean start.
The best results come from overseeding right after aeration. Seed falls into the holes and lands on bare soil, where it germinates far better than seed thrown on top of an untreated lawn. A light top dressing of compost or soil and a round of fertilizer finish the job.
Timing matters. In Southwest Washington, early fall is the best window, when the soil is still warm, rain is coming back, and weeds are slowing down. Spring is the second-best option. Most lawns benefit from aeration once a year, and heavily used or clay-heavy lawns do well with spring and fall treatments.