During a red flag, I don't believe there is a way to see the weather. There have been times where I put on inters only to have the track dry up a few laps later. I couldn't see the weather ahead which makes things a lot harder.
Currently, I would pause the game before the red flag actually takes place and look into the strategy page to see what the weather is. It works, but not ideal. Would like to have an easy way to view the weather during red flags. Thanks!