Facts on Hail in NSW

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.

Selection of hailstones that fell in Sydney suburb of Paddington on the evening of 14 April 1999 (left). Hail blankets the ground like snow in the New England city of Armidale on 29 September 1996 (right). Some of the Armidale hailstones reached 8 cm in diameter whilst the Sydney hailstones reached at least 9 cm.

Large hail (defined as 2cm or more in diameter) is common in New South Wales with an average of about 45 reports each year. Large hail can occur in any month, but is particularly common from September to March, and reaches maximum frequency in November and December.

The largest confirmed hailstones in each New South Wales weather district to June 2003 are:

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 New South Wales include:

• 13 October 2002 – Walcha (Northen Tablelands) - 6cm hailstones. A tornado was recorded in Niangala destroying 2 houses and damaging hundreds of trees.
  
• 16 January 2002 - Kingscliff (Northern Rivers) - 7cm hailstones. Storms with hail, damaging winds and very heavy rainfall affected many centres along the north coast with the SES receiving around 1100 requests for assistance.
• 17 January 2001 - Casino (Northern Rivers) - 7cm hailstones - with damaging winds and several injuries. The SES received 550 requests for assistance.
• 6 January 2001 - Dubbo (Central West Slopes) - 4cm hailstones with drifts up to 1 m high, with very heavy rainfall and severe winds. The roof of the major shopping centre collapsed. The SES received 800 requests for assistance.
• 3 November 2000 - Sydney (Metropolitan) - Many reports of hail ranging from 2 cm to 7cm at Yennora and Greystanes. There was also considerable wind damage and the SES responded to 300 requests for assistance. Three tornado tracks were observed during damage survey.