On Thursday 13 December 2018, a slow-moving low-pressure system developed over south-east Australia, causing severe thunderstorms across eastern New South Wales lasting several days. As a result of these storms, the NSW State Emergency Service (SES) received over 5,300 requests for assistance from impacted communities and natural disaster declarations were made in 14 NSW local government areas. The most significant damage was reported across the Greater Sydney region.

These severe thunderstorms produced more than 30,000 lightning strikes, large hailstones, destructive winds and intense rainfall and flash flooding across Sydney, the Blue Mountains and Central Coast regions. NSW SES received an additional 6,314 requests for assistance and 9,837 calls to the state operations centre as a result of the 20 December thunderstorms, and deployed more than 500 SES volunteers. Additional support was provided by the NSW Rural Fire Service, Fire and Rescue NSW, NSW Volunteer Rescue Association, Ambulance NSW, NSW Police Force and the ACT SES.

As at 17 July 2019, the insured loss caused by the NSW December thunderstorms was an estimated $1.313 billion, with 125,600 domestic insurance claims and 12,195 commercial claims. While one of the costliest events in Australia in 2018, impacts were significantly less than the April 1999 hailstorm that impacted Sydney. In today’s dollars, insurance claims for that event approached $5.6 billion.