This article focuses on winter storms. For additional meanings, please refer to the Winter storm (disambiguation) page. The term “snowstorm” is also redirected here; for other contexts, see Snowstorm (disambiguation).
Members of the National Guard clear a road obstructed by fallen trees following a February 2021 winter storm in Putnam County, West Virginia. A winter storm occurs when wind interacts with various forms of precipitation that take place at or below freezing temperatures, including snow, rain mixed with snow, or freezing rain. While these storms predominantly occur during winter, in temperate continental and subarctic regions, they can also happen in late autumn and early spring. A snowstorm characterized by strong winds and reduced visibility is known as a blizzard.
Formation
Winter storms develop when moist air rises into the atmosphere, resulting in lower pressure at ground level and the formation of clouds. This rising air, known as lift, can be further propelled by geographic features such as hills or large mountains. The wind gathers moisture from expansive bodies of water like lakes or the ocean. If temperatures are below freezing (0 °C or 32 °F) near the ground and in the clouds, precipitation will manifest as snow, mixed rain and snow (sleet), ice pellets, or graupel (soft hail). Cold air holds significantly less moisture than warm air, leading to lower overall precipitation totals compared to warmer conditions.
Winter storm warnings are typically issued under the following circumstances:
- Snow accumulation reaches 6 inches (15 cm) or more in 12 hours, or 8 inches (20 cm) in 24 hours.
- Blowing snow significantly reduces visibility across large areas with wind speeds less than 35 mph (16 m/s).
- Ice accumulates to 0.25 inches (0.64 cm) or more on surfaces.
- Ice pellets surpass 1 inch (2.5 cm) in size.
- Wind chill temperatures drop below -35 °F (-37 °C) for more than 3 hours, coupled with sustained winds of at least 10 mph (4.5 m/s). Snowstorms with wind speeds exceeding 35 mph (16 m/s) and visibility reduced to less than 0.25 miles (400 m) for three hours or longer are classified as blizzards.
Terminology
Severe winter weather conditions, known as “winter storms,” can manifest as localized weather events lasting 24 hours or as expansive storm systems affecting parts of a continent for several days. In cases of extensive winter storms, the term “storm” is often applied to the broader area, even if all locations within it do not meet the specific meteorological criteria for winter storms. A notable example is the North American winter storm from February 13 to 17, 2021, which brought snowfall and below-freezing temperatures as far south as Texas and the Gulf of Mexico.
Snowstorm
In places like Oulu, Finland, snowstorms generate substantial snowfall, with even 2 inches (5.1 cm) leading to significant traffic and school transportation disruptions due to hazardous driving conditions. This is particularly critical in regions where snow is infrequent. Conversely, in areas accustomed to snow, such minor accumulations are less disruptive due to efficient snow and ice removal practices, widespread use of all-wheel drive vehicles, snow tires, and drivers’ familiarity with winter conditions. Snowfalls exceeding 6 inches (15 cm) typically disrupt activities universally.
Historically, the United States has experienced numerous severe snowstorms, including significant blizzards in 1888, 1947, and during the early to mid-1990s. The snowstorm of 1947 saw over 2 feet (61 cm) of snow, with drifts and piled snow from plowing reaching up to 12 feet (3.7 m), lingering for months without sufficient melting. The 1993 “Superstorm” was another notable blizzard affecting many areas.
Severe snowstorms can be highly dangerous; for instance, a snow depth of 6 inches (15 cm) can render unplowed roads impassable and trap vehicles in the snow. Snow depths exceeding 12 inches (30 cm), especially in typically warmer climates, risk causing roofs to collapse and can lead to power outages. The weight of wet snow can also bring down standing dead trees. Even several inches of dry snow can create substantial drifts when winds are strong.
Hazards from snowfall
Accumulated snow significantly increases the risks associated with driving. Snow-covered roadways reduce tire friction, impairing vehicle maneuverability and decreasing average driving speeds by up to 40% during heavy snowfall. Visibility declines with falling snow, and strong winds can worsen conditions, leading to whiteout scenarios where visibility narrows to only a few feet. These hazards may persist even after the snowfall ceases due to winds redistributing fallen snow onto roadways, potentially creating blizzard conditions if winds are sufficiently strong. Vehicles immobilized by heavy snow face dire risks if rescue crews are delayed, and snow blocking a vehicle’s tailpipe can lead to carbon monoxide buildup inside the cabin.
glowblogger.comDepending on atmospheric temperature profiles, snow can be classified as either wet or dry. Dry snow, being lighter, is easily transported by wind and penetrates more effectively. In contrast, wet snow possesses greater weight due to its higher water content, leading to potential roofing damage from excessive accumulation.
