I tend to look at wind gust speed only. Wind gusts would have to be around 31 mph or higher (50 km for the Canadians and the rest of the world) before I would hesitate to go. Today for instance is a no go. Funny only this year I started looking at wind speed. Maybe because I started riding in rural areas for hours at a time and this issue was becoming more important. In the city I don't care so much, though today I still wouldn't ride.