Sleet is a general term for frozen precipitation that is used with two distinct senses in English. In North American meteorology, sleet most often means small ice pellets that form when melting snow refreezes before reaching the ground. In many other English-speaking areas, sleet commonly refers to a wet mixture of rain and snow or partially melted flakes. Because of this split in usage, local context is important when interpreting forecasts and reports.

Characteristics and formation

Ice-pellet sleet develops when snow falls through a relatively deep layer of above-freezing air and melts into liquid drops, then passes through a sufficiently cold layer near the surface that the drops refreeze into hard pellets. These pellets are generally small, often a few millimetres across, and tend to bounce on impact. The rain–snow mixture called sleet occurs when precipitation encounters only a shallow near-surface subfreezing layer, producing partially melted flakes and slush rather than discrete pellets.

  • Freezing rain: falls as supercooled liquid and forms a smooth, adherent glaze on contact with surfaces.
  • Graupel: consists of snowflakes coated with rime ice and is soft, white, and crumbly.
  • Hail: forms in strong convective updrafts and produces larger, layered ice stones associated with thunderstorms.

Occurrence and forecasting

Sleet is most frequent in winter and in frontal situations where warm air overrides a colder layer near the ground. Forecasters use vertical temperature profiles from soundings, numerical models, surface observations and radar signatures to distinguish pellets, freezing rain and mixed precipitation. Small changes in the depth or temperature of the warm and cold layers aloft can change the precipitation type over short distances.

Impacts and precautions

Ice pellets accumulate as loose granular layers that can reduce traction but are generally easier to remove than glaze ice from freezing rain. Mixed sleet or rain–snow conditions produce slush that can refreeze into compacted ice. Hazards include slippery roads and sidewalks, reduced visibility, and complications for air and road travel. Recommended precautions include slowing down, increasing following distance, using appropriate footwear, and checking local forecasts that clarify regional meanings of "sleet."

Terminology and notes

The word "sleet" has longstanding use in English, but its exact meaning varies by country and by forecasting service. When precise information is needed for safety or planning, consult the issuing meteorological agency to learn whether sleet refers to ice pellets, a rain–snow mix, or both in that locality.