When you have poor visibility people have a tendency to lean forwards towards the windscreen in a subconscious attempt to see anything a little better. And when they do that, they also tend to step on the accellerator a little harder.

This also happens in blizzards and during rain at night.

If they happen to see the rear lights of a car in front, they tend to 'glue themselves to it' and rear-ending those who drive safely.