On 9 December 2007, in the north-west suburbs of Sydney, a severe thunderstorm with strong winds and hail caused widespread damage from Blacktown to Wahroonga. The largest confirmed hail size was seven centimetres at Blacktown and six centimetres at Wahroonga; there was an unconfirmed report of 11 centimetre hail at Cherrybrook.
On the Central Coast, a thunderstorm with very heavy rain and strong winds was reported. Wind gusts reached 85 kilometres per hour at Mangrove Mountain. Thirty-six millimetres of rain at Terrigal and 30 millimetres at Newcastle was recorded within 30 minutes. At Mount Seaview there were thunderstorms all day with heavy rain up to 81 millimetres from 9:00am to 8:00pm.
Approximately 20,000 homes lost power and there were more than 6,000 calls for assistance received by the State Emergency Service. Trees were uprooted and houses and motor vehicles were damaged. More than 30 people were treated for cuts and bruises from the storm.
The Insurance Council of Australia estimated the 2007 damage at $415 million, with the 2011 estimated normalised cost of $486 million.