A bug in watchOS 10 that makes Weather data incorrectly displayed on the Apple Watch has been discovered and reported.
watchOS was recently made available to the public and Apple Watch users. However, some have begun experiencing issues with the Weather app not displaying complications on the Apple Watch screen and took to the Apple support community, forums, and social media to share the issue.

Apparently, Weather complications present a blank screen instead of showing data. A quick screen tap makes the data pop out and available to view. The issue is believed to occur on Apple Watch models running watchOS 10.0, as well as the 10.0.1 update.
Users have posted temporary workarounds by opening their iPhone’s Watch app and enabling the 24-hour time setting on the Clock app and going back to the original option. After the update, the complication should display correctly. However, it’s best to wait until Apple issues a patch or fix.