Right now my favorite weather app for my Lumia 920 is
Amazing Weather. That link will take you to the marketplace and you can do the free version or do a trial of the paid version. Great app.
The devs are also doing a beta right now and have put out a call for help testing it inside our forums. If you want to sign up, check this
thread out. Otherwise you can wait for the current version in the
marketplace to be updated.
Another favorite of mine is
Weather Flow. Really clan design and was wonderful on my 7.5 devices. The devs are also updating it to take advantage of WP8 specific features like wide live tiles, lockscreen, etc. You can always download it and try it out and wait for the update when it come out.
Hope that helps!