Easy 6 miles today. Lots of snow in the forecast for today so I didn't want to go too late in the day knowing that it would be harder with all the fresh snow on the ground. Temp was -8C/19F but the wind chill forecast was -17C/1F.
You can't really see it but the snow was blowing horizontal because of the crazy wind. Still I enjoyed it and started sweating quite a bit. However because of the wind chill I didn't take any layers off.
According to wikipedia wind chill is the "perceived decrease in air temperature felt by the body on exposed skin due to the flow of air." If you stand still in air that is 20 degrees F and there is no wind, your skint will be warmer than 20 degrees. Wind carries some of that heat away and the faster the wind the faster the heat loss. Once the wind surpasses 25 mph or so, it whisks away heat more quickly than your body can emit it.
That is important information. First of all I hate to feel cold so I rather overdress, do a warm up, come home and adjust my layers. Second if the wind chill is bad it means ones you cool off you really don't warm up anymore, at least not outside. So if the wind chill gets real bad like -20F or below than I don't go too far from home. That way I can go home if I start to feel cold. No need to take unnecessary risks.