Railworks America

I got that in Railworks 2 also. Only appeared on a few routes.

Maybe it's RSC's version of a tornado?

What is your in game detail set at? High (10) should get rid of that kinda weird stuff. Not the launch screen settings, the in game settings. I have found they are seperate.

Perhaps it's a new form of cloud computing rather than just a cloud topping?

It forces you to be Internet connected when running or no nice clouds

GaryG