Weather is showing —. But when I touch the — the screen shows it

The first (and simplest) thing to try if something isn’t working right is to restart your Apple Watch and its paired iPhone. If necessary (device not responding), try a forced restart. Both methods can be found here:

How to restart your Apple Watch - Apple Support

Restart your iPhone - Apple Support

If that doesn't help, the next steps would be to unpair and pair your watch again and restore from the backup just created. This should result in no loss of data. It deletes all temp and corrupted files and re-indexes the file system.

Unpair and erase your Apple Watch - Apple Support

Set up your Apple Watch - Apple Support

The same thing was happening to me. Temp display was showing “—”. None of the solutions I read worked. I posted an answer, but left out one part: Go to Settings>Privacy and Security (that’s what I left out of my answer)>Location Services>Weather. Then select Always (mine was on While Using). Once I did that, the temperature display came on and has remained on ever since.