Blizzards and White-Outs
In many ways blizzards and white-outs are related. A white-out is a condition found in polar regions in which snow and low cloud layers create uniform lighting, causing landscape features to disappear. For a storm to be qualified as a blizzard, the winds must be blowing in excess of 35 mph and visibility must be reduced to less than 1/4 mile for more than 3 hours. This qualifying wind strength is the main difference between blizzards and white-outs.
There are three different conditions that cause a white-out. During a blizzard snow already on the ground or heavily falling can reduce visibility to near zero, thus causing a white-out. The second type of white-out is caused by heavily falling snow that does not qualify as a blizzard. The snow is falling thick enough to obscure objects. This only occurs with lake or mountain effect of snow. Even when there is little or no snow falling a white-out may occur. Diffused lighting from snow covered ground and overcast clouds can cause all surface definitions to disappear, making it impossible to discern the distance to a snow covered surface. In polar regions, whole mountains can become invisible against a white clouded background. This illusion is also known as flat light or sector white-out.
A blizzard, on the other hand, is usually accompanied by heavy snowfall and severely low temperatures, but are not necessary. There are times when strong winds pick up snow that has already on the ground. The National WeatherService officially defines blizzards as large amounts of falling snow or, large amounts of blowing snow. A blizzard, like a white-out, is also accompanied with low visibility or none at all.
Blizzards and white-outs are equally dangerous. A blizzard poses a threat to drivers and can cause hypothermia and frostbite when wind chill is a factor. Wind chill is the amount of cooling one feels when strong winds and low temperatures near freezing combine. This can feel as cold as still air that 35 degrees cooler. White-outs also pose threat to drivers, but also, to mountain climbers, skiers, and aviation.