I won't ride if it is foggy, despite the fact that I have a blinkie attached to my bike. My reasoning follows what I was told when I lived out in Arizona and had to beware of dust storms: If you stop and pull off the road and you have any lights on in that situation, cars behind you may think that your lights guide them along the road and you run the risk of being rear-ended. That's my main fear - being rear-ended because the driver doesn't have time to react.