What happened?

I was just looking at my avg Speed for the two rides that I did yesterday.

What happened to my speed? I could cruise comfortably at 20mph towards the end of summer. I figure wearing heavy riding boots and a windbreaker are going to slow me down but the main culprit could be my training plan. This plan has me doing base miles for - Hills up to 4%, HR mainly in zone 1 & 2, and "comfortably high cadence".

I am a bit skeptical about two things. Where my zone 2 is and the benefits of "high cadence". We will see, I am keeping track of all my vital stats including Avg speed. If I stick with the plan, my avg speed should go up right? Only time will tell.