On 21 January 1991 severe thunderstorms moved across the northern suburbs of Sydney during the afternoon. Strong winds and large hail stones caused extensive damage. Hail stones up to 7 centimetres (2.8 in) in diameter and flash flooding was reported in several locations. Some areas received more than 35 millimetres (1.4 in) of rain in 6 minutes and more than 60 millimetres (2.4 in) in half an hour. Areas of most severe damage stretched from the Warrawee–Turramurra area to Duffys Forest, with significant damage occurring to property in the Ku-ring-gai, Hornsby and Warringah council areas. More than 7000 houses were damaged. The total estimated insurance payout for the storm was estimated at A$215 million.