1. It will blow in all directions at once
2. A tailwind is a mythical thing, not experienced by anyone living
3. Battling into a headwind, knowing you're returning to base in a loop will NOT see you benefit from the Mythical tailwind mentioned in rule no. 2. The wind will either drop, or more likely, will have changed direction and you'll be into a headwind all the way back to base.
4. Introducing cunning by actually daring to plot your route so as to take account of wind direction, will ENRAGE the wind-gods and they shall strike-down upon you a headwind like you've never seen - you'd better learn how to cycle horizontally!
Right, now we've clarified the rules, I'm going to go to Yachting-School and learn how to tack.
Despite it all, good to be out on the bike knowing it's more miles (42 actually), more training and a step (pedal-crank) closer to the Grand Canyon challenge, all for Brain Tumour Research.