Wind. We lost our first 5er to wind. A blowover west of Laramie, WY. Wrong place, wrong time when a mighty gust hit us broadside. Spread the jaws of the hitch open & the kingpin tore out saving us & the truck from going over a 50' embankment with the trailer.
Had we been a class A or C we would have been toast. The gust was that strong.
These days we are very aware of wind. We watch ripples & their direction on ponds as we pass. We look at flags. We look at leaves on trees. We look at wind blowing grass, anything to give an idea of direction & velocity.