DISCLAIMER: I’ve picked up this information from several different Facer Community posts, so this is just my overview of the issue.
Facer uses OpenWeather (https://openweathermap.org) for their weather source. OpenWeather does not use your “exact” location (no matter what your watch says) and just gives the region wide weather which can be different from where you are now.
You have to make sure your phone is not set to use power management (Adaptive Battery) where it closes “unused” background apps, or at least exempt the Facer app from it.
Next I’ve found that my weather updates more regularly if I open the Facer app 3 or 4 times during the day. There have been lots of times where I’ve looked at my watch and thought that the temperature was wrong, opened the Facer app, closed it and checked my watch and it be close to correct.
NOTE: I’m using a Galaxy S3 Frontier and an Active 2 watch for my daily carry. I also have a cheap TicWatch E that I use only for testing and it seems to have the same issue and cure.
These are my personal observations and are of course subjective: Your Mileage May Vary!