We just cleaned them in late spring, so we were both a little surprised at how much had built up again in so short a time. atara speculated that we trapped more leaves than usual because this autumn has been much milder, and less windy than past ones, so the leaves hung around longer and did not blow away like they usually do.
Sounds plausible to me.
We also got our winter tires swapped in on Monday since we are already well past the normal date for the first serious snow of the year. On the same day that they were changing out the tires, Environment Canada updated their weather forecast for the week to include a severe, snow-bearing winter storm for later in the week. I love it when a plan comes together.