Ever look behind the cab of a trailerless 18 wheeler after a rain ? The wind swirls around over the roof and you can see it travel
upwards behind the cab.
It resembles steam rising from the chassis. ( You can see it vortex )
I find that the best conditions for this are right after a rain when the roads are still wet and there is lots of humidity in the air.
Metro : I posted this a long while ago on that thread. Now I'm going to have to hunt it down.
