A blizzard is a severe winter storm characterized by strong sustained winds and low visibility, lasting for a prolonged period of time, typically at least three or four hours. The National Weather Service defines a blizzard as a storm with large amounts of snow or blowing snow, winds greater than 35 mph (56 kph), and visibility of less than a quarter mile. The difference between a blizzard and a snowstorm is the strength of the wind, not the amount of snow. Blizzards can have an immense size and usually stretch to hundreds or thousands of kilometers. Blizzards can create life-threatening conditions, and traveling by automobile can become difficult or even impossible due to "whiteout" conditions and drifting snow. Blizzards can occur all over the world, but places closer to the Arctic, such as Russia, central and northeastern Asia, northern Europe, Canada, and the northern United States, experience more blizzards than other parts of the globe. Scientists believe that as global temperatures continue to rise because of climate change, blizzards could become more extreme.