Grandine

Grandine, in meteorological terms simply hail, is a form of solid precipitation consisting of ice stones that develop within strong convective clouds, typically cumulonimbus. Hailstones are formed when updrafts in thunderstorm environments repeatedly lift growing ice pellets into regions of freezing temperatures, allowing layers of ice to accrete around a nucleus before they become too heavy and fall to the ground.

The formation process requires persistent strong updrafts, abundant atmospheric moisture, and a temperature profile that includes subfreezing layers aloft. Small hailstones originate near the cloud base and may grow as they are transported upward by updrafts, accumulating concentric layers of ice with each circulation. If the updraft is strong enough or the storm persists, hailstones can reach considerable sizes before they descend. Hail does not form in all thunderstorms and is more common in regions with pronounced convective activity.

Sizes range from small pellets to large stones, commonly a few millimeters to a few centimeters in diameter; exceptionally large hailstones can cause significant damage. The impacts of grandine include damage to crops, vehicles, roofs, and windows, as well as potential injuries to people and animals.

Forecasting and observation involve weather radar, which can identify strong, vertically developed storms with potential hail, and surface reports or hail pads used in research. Mitigation focuses on protective measures for property and agriculture, such as sheltering susceptible assets and, in some cases, insurance coverage. Hail events are most frequent in mid-latitude regions during warm-season convection and can vary with local climate and storm dynamics.