According to the National Weather Service a blizzard is defined as a storm that produces "reduced visibility of one-quarter mile or less for over three hours" and wind gusts of 35 mph or more. In addition blizzards are usually accompanied by temperatures of 20 F (-7 C) and falling or blowing wind. What differentiates a blizzard from a snowstorm is the strength of the wind gusts, not the amount of snow accumulation. However in an urban, crowded area such as New York, a heavy accumulation can create havoc and chaos, even without high winds. In this section, we highlight the worst such experiences in New York City.