This is not an official story but I thought this would be something the site would be interested in taking a look.
So, as I was hunting Google for a picture of the old Portland Thunder Mjolnir Hammer (minus the Shield, Wordmark, and Football) I stumbled upon the Graphic Designer who created the Thunder Logo. His name is Nathanael Clanton. He began designing the Thunder logo in December 2013. The logo was designed in ten days.
Check out the portfolio. You can see the logo sketchbook, home & away uniform concepts (thankfully those were scrapped), logo concepts, prototype helmet mock ups, merchandising designs, website design, promotional posters, and even the Inaugural Season Ticket designs.