A severe thunderstorm caused serious damage to parts of north-west Sydney with a weather pattern suggesting it may have been caused by a tornado or at least a severe 'downburst' in the Turramurra area. The storm hit at around 4pm 21 January 1991 and moved out to sea at approximately 5.15pm.

Estimated wind strengths (based on damage) of 118 km per hour to 230 km per hour brought down many trees (at least 50,000 significant trees were felled or suffered long-term damage). Falling trees damaged over 10,000 houses, with over 100 completely unroofed and 20 totally destroyed. At least 1000 other buildings incurred damage and many businesses suffered extensive damage.

About 140 km of power lines and three steel towers were brought down. (Clean up and restoration of essential services took weeks). Worst hit were the northern suburbs of Turramurra, Lindfield and Wahroonga, while in the west, Seven Hills, Blacktown, Parramatta, Castle Hill, Wollondilly and Dural reported extensive storm damage.

The Insurance Council of Australia estimated the 1991 damage at $138.4 million, with the 2017 estimated normalised cost of $1.04 billion.