DISCLAIMER: I’ve picked up this information from several different Facer Community posts, so this is just my overview of the issue.
First make sure you have all the permissions for Facer granted on both the watch and phone. You must have location turned on in both or the Facer watch app will not have any weather information.
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. Some have said that if you install the OpenWeather app on your phone, it will help the weather stay updated.
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.
Also if you have checked, and everything above is correct in your watch and phone, try restarting both. I’ve noticed that all my watches and phones sometimes need a restart. I now restart everything on every Friday.
NOTE: I’m using an original Galaxy Watch, a Galaxy S3 Frontier, a Galaxy 4 “Active”, and a Galaxy 4 Classic as my daily carry watches. I also use a Fossil Carlyle watch for testing my watch designs on. They all seem to have the same issue and cure.
These are my personal observations and are of course subjective: Your Mileage May Vary!