Looks like it is working so far for me.
I did have to reboot the watch.
Here is what I did:
In the app: Enable weather forecast, go to settings, confirm changes twice.
It didn't show up right away, but after I got another notification on the watch it was there.
Just press the lower button once, and it pops up after the status info and date. (6 degrees here, chilly...)
You can also try doing all of the above a second time if it doesn't take (recommended by Martian).