Adelaide, Melbourne and Sydney could all hit 40 degrees before the weekend arrives.
Temperatures have been far milder across Australia's southeast in the last day or two. Adelaide had its first rain in four weeks and Sydney had its first rain of January, both gaining 9mm.
Many people are enjoying the reprieve from the heat, but it's still tough work for firefighters who are trying to contain blazes before the heat returns in coming days.
Adelaide and Melbourne will be very hot on Thursday as northwesterlies develop through South Australia, Victoria and western parts of New South Wales. The hot, dry and gusty northwesterly winds will lead to increased fire danger on this day, similar to recent weeks. Both capitals are currently forecast to reach 39 degrees with a good chance of tipping 40 degrees in the blazing sun.
On Thursday afternoon a cool southwesterly change will reach Adelaide, but it won't reach Melbourne until night-time when it will be quite weak, leading to a warm night.
On Friday this change will be brought into NSW by a low pressure trough. Northwesterly winds ahead of the trough will push into Sydney where western suburbs are likely to reach the low 40's. The city is also a risk of these temperatures if the northwesterly winds hold out the sea breeze long enough.
Fire danger will be elevated again across New South Wales on Friday as winds will be moderate to fresh and temperatures will rise into the 40's in many parts of the state.
For those who don't like the heat, relief will come in the form of a gusty cool change for Sydney during the late afternoon or evening, dropping temperatures suddenly.
Saturday and Sunday will be milder across Australia's southeast. Adelaide and Melbourne will both enjoy a mostly sunny weekend. Sydney will get temperatures in the mid 20's and a combination of a few showers and sunny breaks.
© Weatherzone 2013
18:43 EDT Severe thunderstorms and damaging winds have caused chaos across Sydney, with the SES looking at more than 250 jobs, mainly roof damage from heavy rain and strong winds.