A pulse of Antarctic air will cause Australia's first widespread snowfall for 2018 at the end of this week. A stray low pressure system venturing north from the Southern Ocean will cause temperatures to plummet across Australia's southeast in the coming days. It is likely to get cold enough for snow to settle in Tasmania from Wednesday and in Victoria and NSW from Thursday. As the frigid air creeps further north during Friday and Saturday, snow could fall to low levels along the Great Dividing Range. This system is likely to bring the first decent bout of snow for the year in Australia's alps. Models suggest that around 20-40cm of natural snow will accumulate in the alpine region between Thursday and Sunday. Outside the alps, snow is forecast to reach down to 800-900 metres above sea level in central and western Victoria and over the Central Tablelands of NSW by Friday. Flakes may even fall over the Northern Tablelands of NSW if the cold air reaches far enough north during Friday night or Saturday morning. While May snow is not uncommon in Australia, this is an unusually cold system for this early in the year. Melbourne is forecast to reach highs of 13 degrees on Thursday and Friday, which would be the city's coldest pair of days this early in the season since 1978. Canberra's forecast top of nine degrees on Friday would be the city's coldest day this early in the year since 1970. Friday is also forecast to be the coldest day this early in the season for seven years at Thredbo (-3C), Cabramurra (0C), Ballarat (9C), Bendigo (12C) and Deniliquin (13C).