Definition of Graupel

Commonly known as soft hail or snow pellets, Graupel denotes a form of precipitation. This precipitation category arises through the collection and freezing of supercooled water droplets on descending snowflakes. The culmination of this process is a ball of rime ice, typically measuring between 2-5 millimeters.

Formation of Graupel

Graupel comes into existence under cold and humid conditions wherein the atmospheric temperature resides below the freezing point. Supercooled water droplets present in the air, though in a liquid state below their freezing point, necessitate a nucleus to facilitate the formation of a crystal structure. In this scenario, a snowflake provides the requisite nucleus. Upon encountering the snowflake, the water droplets freeze instantaneously, precipitating the creation of a rime layer. This phenomenon is termed accretion.

Graupel vs. Hail and Sleet

Graupel, hail, and sleet are often mistakenly considered identical, despite their distinct attributes.

Hail, a variety of solid precipitation, forms within thunderstorms and exhibits a size typically larger than that of graupel. Hailstones originate as petite ice pellets and augment in size through collisions with supercooled water droplets, which subsequently freeze onto the hailstone's surface.

In contrast, Sleet comprises raindrops that transform into ice pellets prior to reaching the ground. The genesis of sleet transpires when a stratum of air exceeding the freezing point is sandwiched between the earth's surface and an elevated layer of air registering sub-freezing temperatures.

Unlike hail, graupel is generally soft and crumbly with a size conventionally less than 5 millimeters.

Effect of Graupel on Weather Conditions

Impacts of graupel on weather conditions are manifold. It hampers visibility and transforms surfaces into slippery expanses. The presence of graupel often implies a cold and unstable air mass. Moreover, graupel can serve as an indicator of harsh weather conditions, showing association with thunderstorms and occasionally preceding hail formation.

Graupel in Meteorology and Weather Forecasting

Graupel holds substantial importance in meteorology and weather forecasting. An in-depth understanding of its formation processes equips meteorologists to anticipate harsh weather conditions. To illustrate, if graupel is present, there could be potential for hail formation, provided the atmospheric conditions foster the development of thunderstorms.
Updated: Jun 2, 2023
Published by: Weather U.S. | About Us