Extreme heat will crawl across southern Australia next week, making the mid-December heat look mild by comparison. In mid-December, Adelaide exceeded 39 degrees for three days running and Melbourne also notched up one day of 39.9 degrees. Canberra saw three days in a four day stretch exceed 35. Starting on Monday, one of the fiercest heatwaves on record is heading to the south. Adelaide's working week will be like a furnace with all days, except maybe Friday, likely to go into the very high 30's or low-to-mid 40's. The very hot air mass feeding in from Western Australia will slowly move across South Australia before a cool change finally arrives on Friday. From Monday morning to Friday night there is a good chance the temperature will not drop below 25 degrees. Melbourne is also looking spectacularly hot next week. On Tuesday the heat will surge in, reaching the low 40's. There might be less heat on Wednesday and Thursday, while still soaring in the 30's before a final peak on Friday in the 40's again. A cool change will then move through that night, but by then many will be struggling from the heat. Canberra is not one to be left out. A heatwave with five days over 35 degrees is now likely from Tuesday to Saturday with even a slight chance of nudging 40 degrees on one day. This will be almost identical to the heatwave of early January last year. Sydney is not looking like getting this heatwave due to the dominance of seabreezes. However western Sydney should see multiple days climb into the high 30's beginning mid next week. Inland parts of southern Australia will see heatwave conditions across this period with many low-lying areas likely to reach the low-to-mid 40's on consecutive days.