Winter Weather Precipitation

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Winter is raising its head so here are a few definitions of winter precipitation types. The information is adapted from the Glossary of Meteorology published by the American Meteorological Society in 1959.

  • Snow is composed of white or translucent ice crystals, chiefly in complex branched hexagonal form and often agglomerated into snowflakes. In other words, snowflakes are made up of individual ice crystals stuck together in groups of many ice crystals. Snow that falls through a deep wet layer after forming may grow into large snowflakes while falling toward the ground. If snowflakes form and fall through a dry layer layer do not grow into large flakes. The shape of ice crystals is mostly determined by the temperatures at which they develop and grow.

  • Snow pellets, also called graupel or soft hail, are white, opaque ice particles approximately round or conical in shape. They form when super-cooled water collects on ice crystals or snowflakes. Super-cooled water water that is below freezing. Snow pellets usually bounce when they fall on a hard surface and often break into smaller pieces.

  • Snow grains are very small, white opaque particles of ice. They are the solid equivalent of drizzle. They resemble snow pellets in external appearance, but are more flattened and elongated, and generally have diameters of less than 1 millimeter; they neither shatter nor bounce when they hit a hard surface.

  • Ice pellets, or sleet, are small balls of ice that form from the freezing of raindrops or the refreezing of melting snowflakes when they fall through a layer of below-freezing air near the surface of the earth.

  • Freezing rain occurs when rain hits a surface with a temperature that is below freezing. As the drops fall through a layer of sub-freezing air near the earth’s surface, they become super-cooled, which means the drops are below freezing but are still liquid water. When the drops hit the surface, the splattering disturbs the liquid drops, causing them to freeze instantly. Freezing rain forms a dangerous coating of ice causing falls, broken bones, and automobile accidents.