In the last few days the Weather XML stopped working on my Sharepoint site. Coincidentally I'd received an email from Weather.com regarding their service.
Weather.com now seems to require a partner ID in addition to the key. You will want to sign in to their XOAP page to update your agreement and get a partner ID. I have updated the original post with a new URL. I have also updated the XSL template to include the promo links which are apparently required by the license agreement. If you had previously downloaded my XSL template, you should update your template to the latest version.