Where does the water go over the winter?

I have 28ft round AGP. Every fall when we put the cover on, the pool is full up to the return and skimmer. We don't use any floating pillows or anything, just lay the cover on the water.

Come springtime, after we pump the standing water off the cover, the pool is down by about half. Before we pump it off, the covered pool looks full. It's just half full above the cover and half full below the cover.

The skimmer and return are plugged for the winter. So the water has nowhere to go.

I assume it just evaporates. But you don't think of water evaporating during the winter. Why doesn't the water on the top (that I don't want) evaporate? Instead it evaporates the water under the cover (that I want to keep).

We just took the cover off yesterday, and it's a big group project. We pump and pump the cover, but there is always water (and leaves) left on top. So we need two people in the pool pushing and 3 outside pulling. It's a big sloppy, messy project and everyone gets wet and muddy. Then we fire up the grill and have a few beers and wonder how long it's going to take to fill the pool and clean it up. This year it looks like about 48 hours for about 6,000 gallons.

---Dale

The water from rain/snow on the cover pushes the water in the pool over the edges.

Moderators, I just realized this should be under spring startup. Please feel free to move. thanks.

as posguy said, some gets pushed out as crap sits on top of cover. Also, small leaks in the cover can let water slowly trickle through, becoming water on top of cover.
Many people will put the water on top into the pool, once it's clean of debris-
I use the pillows to keep the cover up (really to keep the wife happy, she thinks we need them), so don't have the same issues; instead, my pillows sink and are a pain to get out until the water warms!

Of course, when I first read the topic, I was about to say " It hibernates below your house and comes out when the woodchuck says its safe!"