South Australia braces for textbook catastrophic fire conditions tomorrow, New South Wales expects a spike in heat today, and south-east Queensland recovers from a hail hammering as we look at this week's weather focus.

Key points: A cold front is bringing catastrophic fire conditions to South Australia tomorrow.

A cold front is bringing catastrophic fire conditions to South Australia tomorrow. The strong winds are forecast to stay south and miss the major fire grounds currently burning in NSW and QLD.

The strong winds are forecast to stay south and miss the major fire grounds currently burning in NSW and QLD. There is potentially hit and miss rain for parts of NSW late in the week but no widespread rainfall on the horizon.

All eyes will be on South Australia tomorrow as they face potentially disastrous fire conditions as the latest cold front sweeps across the country.

Grace Legge, senior forecaster with the Bureau of Meteorology's extreme weather desk, has the latest.

"We've just had that very warm mass sitting over Western Australia," she said.

"We saw records broken through Saturday and Sunday and now that heat is being pulled further east as the next cold front approaches."

Wednesday is the peak fire danger in south Australia, statewide fire bans are in place. ( Supplied: Bureau of Meteorology )

A cold front is the classic fire set-up for southern Australia and the same conditions led to many of the big fires in our history; Black Friday (1939), Ash Wednesday (1983) and Black Saturday (2009).

The cold front compounds the fire danger by having strong, hot winds that fan flames, followed by a wind change which causes fires to change direction and expand at a horrifying rate.

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"The worst part is where you see the hottest conditions in the afternoon," Ms Legge said.

"That allows the maximum heating before that change goes through.

"That's what's really leading to those quite dangerous fire conditions through South Australia."

What is a catastrophic fire danger rating?

Catastrophic fire danger indicates that if fires get the chance to take off, they will be unfightable.

According to the South Australian Country Fire Service, no house is built to survive these conditions and in the case of a fire the only option is to leave.

They are the type of days we associate with all the extremes of fires, like fire thunderstorms, which is when fires generate a thunderstorm on top of them.

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This brings all the dangers of a thunderstorm on top of a fire; erratic winds, downdrafts and dry lightning — which can start new fires.

Ms Legge said if fires did get burning hot enough, there was always a risk of fire thunderstorms, but they did need moisture to form.

"It is quite a dry air mass, but it definitely can't be ruled out," Ms Legge said.

Another potential danger is spot fires; when burning debris is lifted up in the hot air above the fire and carried downwind.

During the Black Saturday fires in Victoria, spot fires were recorded up to 40 kilometres in front of the fire.

"[On Wednesday in SA], with those strong winds there is always the risk of spotting ahead of it [a potential fire,] the winds are quite strong aloft," Ms Legge said.

"We could see wind gusts getting up towards 80 kilometres an hour and potentially even damaging wind strength, which does mean that there is the risk of spotting ahead of those fires."

East coast may avoid the worst — for now

Ms Legge said NSW was expecting a spike in fire danger today through places like the Hunter and Greater Sydney.

However, it's looking like the worst of the winds will track south of the rest of the mainland, largely sparing the current firegrounds in Queensland and NSW from a repeat of last week's conditions.

There is likely to be an easing of conditions on Wednesday before another increase in fire danger on Thursday, as the hot air that is expected to bring such dangerous conditions to SA moves through.

"From Thursday we'll probably start to see very high fire danger throughout those firegrounds [in Queensland and NSW], just with that warmer air mass moving through," Ms Legge said.

"But as mentioned we're lucky to see the winds not pick up too much.

"So while it still will be dangerous around the fires, they won't be as fast-moving as previously seen."

Until there is widespread rainfall these fires will keep burning.

When will it rain?

It's not looking good.

Ms Legge said there could be a bit of rainfall for New South Wales as the cold front that was bringing damaging fire conditions to SA Wednesday moved further east.

But she said any precipitation would most likely be in the form of showers or thunderstorms and would not arrive until late in the week, as the system gets closer to the east coast and manages to drag in some moisture from the north.

There may be a bit of rainfall around late in the week and into the weekend for parts of New South Wales but it is expected to be patchy. ( Supplied: Bureau of Meteorology )

"It is a convective set-up, so it would be quite hit and miss for where we get the rainfall," Ms Legge said.

"And unfortunately, because it is still quite dry underneath, we probably wouldn't expect too much rain at the surface.

"And with lightning there is the risk that it could actually start more fires."

Where did Queensland's giant hail come from?

Speaking of moisture, Queensland broke up the fire news late Sunday with a super cell thunderstorm and giant hail.

While this was not unexpected, it was still remarkable considering the dry atmosphere which has been fuelling bushfires for weeks.

"They had a little bit more onshore flow going in, which allowed that moisture to come off the coastal areas, which did allow those thunderstorms to develop," Ms Legge said.

While it was destructive, Ms Legge pointed out that kind of thing does tend to happen in Queensland.

"Queensland generally does have a storm or two like that," she said.

"Through areas of southern Queensland and into north-east NSW it is not unheard of to see those storms — especially with hail that sort of size.

"That's generally the area that it does happen most often, but that being said, actually getting it in an area is still not an event you'd expect to see every month."