Day 323/18. All at once, a garden full of leaves

Last Friday, before we went away for the weekend, there were almost no leaves down from our big Oak trees at all. The lawn was green, we could see all of it. A few leaves were blowing around.
Today? Well, look at the picture. It seems that either the temperature or the winds helped the Oak trees to decide to shed their leaves all at once. While we were away.
We don't remember it happening so fast in previous years. Is this a sign of something, weatherwise?