Not all weather widgets are coded the same, and as such, the location.js fix mentioned doesn't work in some cases. This is one of those areas where you're very comfortable working with HTML, you're best off checking to see if the widget's designer has released an updated version. Many updates have been posted over on ModMyi; some in the theme threads, some in the iWidget thread, some in the UniAw one (that's also where you can find the updated location.js file.)
Unfortunately there's no magic solution to fix them all. Hopefully designers will update theirs as they become aware of the problem, but if you didn't get a particular widget via Cydia, you may have to hunt a bit to find where an update was posted.