Severe Thunderstorms and Hail in Victoria

Temperatures near the tops of thunderstorm clouds are very cold, dropping to around -50 to -60 degrees Celsius even during the summer months. Hailstones form in this very cold environment when super-cooled water droplets freeze onto ice crystals, then grow in size as they are held aloft by powerful updrafts of air within the storm. The hail falls to the ground when it moves outside the storm's updraft, or grows to a size that cannot be supported by the storm's updraft.

Left: A sample hailstone that fell during severe thunderstorms in Lilydale December 2003.    Right: Hail damage to the windscreen of a car after the Lilydale storm. Hail up to the size of softballs (11cm) was also reported. (Photographs courtesy of David Simpson)

Large hail (defined as 2cm or more in diameter) in Victoria averages about 20 reports each year. Large hail can occur in any month, but is particularly common from October to March, and reaches maximum frequency in January. During winter months hail is commonly small in size (less than 2cm).

The most damaging hailstorm to date in Australian history occurred in Sydney, NSW on the evening of 14 April 1999. This violent storm produced hailstones with measured diameters at 9cm, although larger hail would certainly have fallen in the more severely-damaged areas.

Recent examples of hailstorms in Victoria include:

• 02 Dec 2003: In the Eastern suburbs of Melbourne, mainly Lilydale and Doncaster, golf ball sized hail was reported and flash flooding occurred. The SES were called to 100 jobs in the area. One report of hail near softball size was received from Lilydale.

• 05 Oct 2003: St James (Northern Country) Tennis ball sized hail and hail 7cm in diameter reported. Trees were uprooted, and fences, silos and haystacks damaged. Severe crop damage occurred over 2000ha while 6500ha of crop area suffered some damage.

• 23 Dec 2001:  A severe thunderstorm in the Bairnsdale/Lakes Entrance area produced 3 to 4cm hail, heavy rain and strong winds. Trees, plants, crops and buildings were damaged. The SES attended to about 30 calls for assistance.