Is this tire rot in between the thread?

I'm not a tire expert, but I have Fuzion tires with little cracks. seem to be more on the side which gets the afternoon sun. my last tire rotation, i only did front - to - back, not a front criss-cross to the back / back same-side to the front. but I frequently inspect the tires, mainly looking for any chunks out of the tread blocks.

I might get new tires for the winter, but they aren't wearing down much at all