Weather Underground offers a 1-year premium membership for free via the directions below. That's $10 off and tied with our September mention as the best deal we've seen from Weather Underground.
  1. Click here and register a new account (check the "Upgrade my membership.." box
  2. you'll receive a confirmation email at the account provided
  3. in that email, click the link or enter the supplied code to verify your account (you can skip the optional info)
  4. agree to the terms of use
  5. at the payment screen, use coupon code "QWV35" to get the membership for free

If you have an existing account, click on "Settings" and then enter the code at the renew membership screen.