From personal experience: there have been days when it was nice for a bike ride, but I just "wasn't feeling it". Went anyway, and I find I always feel much better-physically and mentally, after a ride.
So, if it's a nice day, go for it! Hopefully, you'll find, as I have, that you're glad you did. Now, whenever I think I might not ride, I just go back to the "memory bank" and that provides the inspiration.