Snowdrift

Snowdrift, in meteorology and snow physics, is an accumulation of loose snow deposited by wind. It forms when wind transports snow material from exposed areas and drops it downwind of objects or terrain, creating a mound or ridge of snow separate from the surrounding surface. The resulting deposit may be shallow or deep and can be highly variable in shape.

Formation and shape depend on wind speed and direction, snowfall properties, surface roughness, and the presence of obstacles such as buildings, fences, trees, or ridges. As air flows past an obstacle, turbulence extracts and concentrates snow on the lee side, while stronger winds can transport finer grains farther before deposition. Drifts often align with the prevailing wind and can grow rapidly after additional snowfall or gusts.

Snowdrifts can range from a few centimeters to several meters in depth. Their internal structure varies from loosely packed grains to more cohesive layers, depending on snow moisture and temperature. They may rearrange, settle, or shift with new winds, rain-on-snow events, or thaw, altering their geometry and stability.

Drifts pose practical hazards. They can block roads, railways, entrances, and ventilation intakes, reduce visibility, and impede evacuation. They also increase avalanche risk on slopes by adding localized loading of snow packs. Management includes windbreaks and snow fences, regular snow removal, and monitoring of drift development in exposed areas.

Measurement and study of snowdrifts inform weather forecasting and road maintenance. Techniques include visual surveys, snow depth measurements, and lidar or radar sensing to map drift extent and movement over time.