A blizzard is a severe snow storm with winds in excess of 35 mph and visibility of less than a quarter mile for more than 3 hours.
Blizzards can also occur after snowfall when high winds cause whiteouts (fallen snow blowing around) and snowdrifts (huge mountains of snow), which decrease visibility.
To avoid hypothermia if caught outdoors during a blizzard, stay hydrated and nourished, keep your blood flowing by moving around, if your clothes are wet, try to start a fire to dry them, create a snow cave to block winds which reduce your body temperature, and do not eat snow (it will make you colder!).