Apple has provided two solutions for resolving issues with the Weather app complication on watchOS 10.
Macworld
If you have an Apple Watch Series 4 or newer and have updated to watchOS 10, you may have observed significant changes. However, there is one modification that has been causing frustration among users, and Apple seems unable to resolve it.
Since the introduction of watchOS 10, numerous individuals have observed that the Weather app complication fails to load, displaying dashes instead of temperature, AQI, or precipitation data. We assumed that the problem would be resolved with the rollout of watchOS 10.0.1 and 10.0.2 updates, but reports indicate that the issue remains.
Apple has provided two options, but they may not be very useful. The initial suggestion is to switch the Allow Location Access feature on your iPhone, which can assist the watch in reconnecting to your current weather. The other option is to completely reset Location & Privacy, which will restore all of your location settings to their original state.
Several individuals have noted that Apple’s recommendations have been effective for a short period of time before returning to the original issue. Others have found success by alternating between the 12-hour and 24-hour clock in the Clock app’s settings.
The problems are expected to continue until the release of the watchOS 10.1 update from Apple, which entered beta testing this week.