Madeleine Reis asks: "Could you explain the difference between freezing fog and freezing rain? And do they both produce black ice?"
Freezing fog happens when temperatures at ground level drop to or below freezing, and the water droplets making up fog freeze on contact. The key is freezing fog involves water droplets.
Now, freezing rain is the name given to rain that falls when surface temperatures are below freezing.
Remember all that freezing rain we had back in December of 2010. Here in Knoxville, the roads and interstates were a mess. Because of the conditions, police even had to stop responding to accidents at one point, all because of the freezing rain and the black ice it caused.
And to answer the second part of your question-- yes, both freezing fog and freezing rain can cause ice.
The big difference is freezing fog involves water vapor. Freezing rain involves rain drops, but they both occur when the ground is at or below freezing.