Sydneysiders have slept through a relatively warm night in sharp contrast to the cold nights earlier this month and ahead of the bitter cold nights this weekend and early next week. The Harbour City managed to only dip to 12.6 degrees (5 degrees above the July average) this night, 6 degrees warmer than that of July the 12th when the mercury dipped to 6.4 degrees. In fact, this was Sydney's warmest night since the 6th of June and 4th warmest so far for the winter. Further west, other centres were also warmer than average, with Sydney Olympic Park dipping to 9.6 degrees, and 9.2 degrees at Bankstown. Relative strong winds averaging 20-40km/h overnight and patchy high cloud were the main factors leading to this unusual warm night. The thin cloudband, has been travelling across the country from the distant Indian Ocean over the past few days, having hitchhiked a ride with the upper atmosphere jet stream. Hence we can see this type of cloud even under high pressure systems. Jet streams are a fast flowing, narrow air currents found in the upper atmosphere in the transition layer between the troposphere and stratosphere. These jet streams are highly valuable within the aviation industry as they are use as the highways of the skies. Travelling in one of these can cut the trip time by about one-third. A warm night and plenty of sunshine today will allow for temperatures to reach the low twenties early this afternoon with mostly sunny conditions persisting throughout the whole week. Wind however, will freshen up later today and persist over the next few days as several cold fronts sweep across Tasmania and southern Victoria. A strong front will then sweep through southeastern Australia on Friday bringing an Antarctic blast with colder days (especially mornings) from Saturday until at least mid-next week.