Even if it were, which it isn't as others pointed out, sometimes free speech takes a backseat to other needs of society. In this case it's the desire to have a

Even if it were, which it isn't as others pointed out, sometimes free speech takes a backseat to other needs of society. In this case it's the desire to have an effective warning system for extreme events such as heavy weather. It obviously wouldn't work if advertisement industry would be able to condition people to ignore it as a false alarm. The same is true for putting lights, writing and sirens on your car which imply you are a member of emergency services.