After a hot Friday Sydneysiders welcomed the relief brought by a "Southerly Buster". What makes a southerly change a Southerly Buster though? There are multiple definitions but one of the more recognised criteria include southerly winds gusts exceeding 54km/h and a temperature drop of five degrees celsius over a three-hour period. Southerly Busters can be significantly stronger than that though. The highest wind gust recorded with a Southerly Buster in Sydney was in December 1948 when winds gusted to 113km/h at the airport. The largest temperature drop occurred in November 1946 when the mercury plunged from 39.1 degrees to 19 in just one hour. Friday night's change moved through Sydney between 7-8pm bringing gusts of 52km/h to the city itself and 61km/h to the airport. The temperature drop was most pronounced at the airport where 5.5 degrees were shaved off the temperature in just six minutes. The CBD recorded a drop of 7.7 degrees in the hour to 8:30pm. Although the CBD didn't quite reach the wind threshold for a Southerly Buster the airport did, making last nights change an official Southerly Buster. It rolled through in time to allow residents to open every window in the house in an attempt to flush out the day's heat, making it a little easier to get to sleep. The downside to the change is that the weekend will be cooler and cloudier. Those in the east can expect tops of around 23 on Saturday while in the western suburbs it will reach the mid-to- high twenties. It will be similar on Sunday but a couple of degrees warmer. It will heat up further at the start of the working week with the city forecast to reach 29 degrees and the low thirties for the western suburbs.