been there done that. Had this problem near Chicago when going from the city to the farms outside the suburbs where I lived. It usually happened in the late Fall, so not only was it foggy, it was also under 50F.

The worst however was a couple times when it was foggy and right at the freezing point. The fog hit you and actually began to freeze on your jacket, visor, widnscreen, etc. After just a short 20 minute ride to meet some guys for breakfast, I was covered in frost and ice.