Excitement and heat are two reasons why people won't sleep in Sydney tonight ahead of a Christmas cool change. Temperatures soared in Sydney today with western suburbs climbing high into the thirties. The city reached a relatively low top of 29 degrees due to the development of a sea breeze during the morning. During the afternoon instability ahead of a low pressure trough has triggered a few thunderstorms in western Sydney that were moving slowly east during the early afternoon. These storms bring the risk of flash flooding due to their slow moving nature and high amounts of moisture in the atmosphere. Any storms or showers that move through will bring a significant drop in temperature. However it's going to stay warm tonight. Temperatures are expected to remain in the 20's throughout the night in the Sydney basin due to the lingering heat. This heat will give extra incentive for children to complain that they can't sleep tonight. Relief will arrive just before sunrise as the low pressure trough moves through bringing a cool southerly change. This southerly will be quite strong along the coast in the morning, while it will be breezy throughout Sydney. Elsewhere in the world people will have a white Christmas, but in Sydney it will be grey. This change brings the risk of showers through the day with most expected to arrive in the morning. Even during the afternoon skies will remain grey and put a dampener on some celebrations. We at Weatherzone hope that you have a wonderful day, despite the showers and cloudy conditions. Southerly winds will remain moderate to fresh on Boxing Day for the start of the Sydney to Hobart. Seas will be rough meaning that the start is likely to be messy. The rest of the day will be fairly cool for this time of year with a top of only 22 degrees in the city.