1.2.4. Downdraft

  • 11 months ago
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  • Author: SW101


Hail is precipitation of hard ice particles – hailstones. By definition, hail is 5 mm or larger in size. Hailstones are generally in the form of balls, but can be irregular in shape, particularly in larger sizes.

How hail forms

Thunderstorms that are characterized by strong updrafts, large liquid water contents, large cloud-drop sizes, and great vertical height are favorable to hail formation.

In Europe the highest number of hailstorms in in the mountainous areas of the pre-Alpine region and across the plains of north Italy. The frequency of hailstorms has been found to be inreasing in southern France and Austria and decreasing in eastern parts of Europe over the past 70 years.

In particular, dry mid levels, at approximately 3-7 km height, are a very favourable factor for hail formation. In dry mid levels rain droplets falling through the dry air evaporate, cooling the air. The cooler air encourages hail formation.

Types of hailstones

  • “Onion skin” hailstones:
  • Aggregate hailstones:

Interesting hail facts:

  • The largest recorded hailstone fell during a severe hailstorm in Vivian, South Dakota (USA) on July 23, 2010. It was 20 cm in diameter and weighed 0.88 kg.
  • The heaviest recorded hailstone was recorded in Gopalganj district, Bangladesh on April 14, 1986. It weighed 1.02 kg.
  • The costliest hailstorm in Europe was