Accretion:
Small ice crystals collect supercooled water droplets by collision, freezing them on the surface and increasing the crystals' size.
Riming:
As the hailstone continues to move within the storm, it encounters supercooled water droplets that freeze onto its surface, leading to further growth and giving the hailstone a white, opaque appearance.
Collision and Accretion:
Larger hailstones collide with and stick together with other hailstones or ice crystals, increasing their overall size. This process creates the larger, more spherical hailstones that we commonly observe during hailstorms.
Hailstone Size:
The size of hailstone depends on several factors, including the updraft strength, temperature, humidity, and the duration they spend within the storm. The hailstone's final size is determined by the balance between the accretion rate (how fast it grows) and the melting rate (how fast it melts as it falls).
In general, hailstone grow through the aggregation of many smaller ice particles, and their growth is influenced by complex atmospheric conditions within the storm. Hailstones larger than 2.5 cm (1 in), commonly referred to as "giant hail" or "golf ball hail," are less frequent but can occur in severe hailstorms. Hailstones the size of grapefruit or larger are extremely rare but have been observed in some severe storms.
Understanding hailstone growth processes and predicting hail size distribution are crucial for assessing hail risk, designing infrastructure for hail resistance, and issuing accurate severe weather warnings to protect communities from hail-related hazards.
