New One M8 User - Couple of questions.

Not sure if you've tried this, but this worked for me. Under settings>location>mode, it needs to be set at either high accuracy or battery saving for weather to show on lockscreen. I had it set at device only before and weather was only available on home. Hope it helps.
 
Not sure if you've tried this, but this worked for me. Under settings>location>mode, it needs to be set at either high accuracy or battery saving for weather to show on lockscreen. I had it set at device only before and weather was only available on home. Hope it helps.

Thanks, 1888744. I was having the exact same issue as OP, with the weather on the lock screen showing "Weather Unavailable" and setting it to high accuracy solved the problem.

Now, here's the part where someone more knowledgeable than me will have to chime in. In order to set high accuracy, I had to agree to let Google collect anonymous usage statistics. But when I hit agree, the next popup said that in a previous version of Android I had disallowed Google apps from knowing my location. So I kept that setting.

So I'm not sure if I just did nothing at all there (because of that second popup) or if Google really is collecting anonymous usage data about me now. Regardless, thanks again 1888744, your fix did the trick!