A blizzard is a severe winter storm that can dramatically alter landscapes and daily life. Understanding the specific characteristics that define such an event is important for safety and preparedness. While many associate blizzards with heavy snowfall, their classification relies on a precise combination of conditions.
The Defining Criteria of a Blizzard
A winter storm is classified as a blizzard when it meets three specific meteorological conditions, as established by the National Weather Service (NWS). These criteria ensure a consistent definition for severe winter weather.
The first condition requires sustained wind speeds or frequent gusts of 35 miles per hour (56 kilometers per hour) or greater. “Sustained” refers to wind speed averaged over a period, typically two minutes, rather than instantaneous bursts. Strong winds are a hallmark of a true blizzard.
The second condition involves reduced visibility to less than 1/4 mile (0.4 kilometers), due to falling and/or blowing snow. Falling snow is precipitation actively descending from the clouds. Blowing snow refers to snow already on the ground being lifted and moved by strong winds, often forming a dense, opaque curtain. A blizzard can occur even without new snowfall, relying solely on previously fallen snow being swept up by the wind, a phenomenon known as a ground blizzard.
The third condition mandates that these severe wind and visibility conditions are expected to persist for a period of at least 3 hours. This duration requirement emphasizes the prolonged nature of the hazard, ensuring that transient squalls do not qualify as blizzards.
Understanding the Severity of a Blizzard
The simultaneous occurrence of high winds and severely reduced visibility amplifies a blizzard’s impact far beyond that of a typical snowstorm. Powerful winds create significant snowdrifts, which can rapidly block roads and trap vehicles. These drifts can become deep enough to isolate communities.
Reduced visibility, often leading to whiteout conditions, makes travel extremely hazardous or impossible. In a whiteout, the distinction between the ground and sky disappears, causing disorientation. Strong winds and cold temperatures also drive down the wind chill, greatly increasing the risk of frostbite and hypothermia. These combined effects can strain emergency services and lead to power outages from damaged infrastructure.
Blizzard vs. Other Winter Weather
It is important to differentiate a blizzard from other winter weather phenomena, as snowfall alone does not define it. A storm with heavy snow but without accompanying high winds and low visibility is classified as a heavy snow event or winter storm. The critical factor is wind-driven snow severely obscuring vision, regardless of new snowfall.
While blizzards typically occur in cold environments, temperature is not a defining criterion for a blizzard designation. A blizzard’s classification hinges strictly on wind speed, visibility, and duration. Therefore, a “winter storm warning” or “heavy snow warning” indicates significant snowfall or ice, but only a “blizzard warning” signifies the specific combination of intense winds and low visibility that defines a true blizzard.