The mercury dipped to minus 0.4 degrees in Richmond in Sydney's north-west on Tuesday morning, while Horsley Park and Camden posted lows of just 1.2 and 1.3 degree, respectively.

The CBD fared better with a minimum of 6.4 degrees - the city's 11th day this month with temperatures dipping below 7 degrees.

With only a few days to go before August,  forecasts indicate Sydney will post its coldest July since 1998 according to the average of day and night temperatures, Brett Dutschke, senior meteorologist with Fairfax Media's Weatherzone, said.

The July result - the coldest for the month this century - is a feat made less likely as climate change lifts global temperatures. Over the past 15 years, the frequency of very cool months has dropped by about one-third compared with the 1951-80 period while very warm months are five times more likely, the bureau said in its latest State of the Climate report.

Other parts of south-eastern Australia have also had a cold July, with Melbourne's daytime temperatures likely to be that city's lowest for the month in 20 years. Adelaide will probably have its coolest July since 1998, Mr Dutschke said.

"The main contributor ... has been a high frequency of fronts, and stronger-than-normal fronts," Mr Dutschke said.

"It's largely because the polar jetstream across Australia has been further north than normal and allowed the cold air to spill further north."

Sydney's outlook for the coming week is for much of the same conditions as of late: generally sunny days with little cloud level, leading to cool mornings and mild days.

Overnight temperatures should dip to single digits each night but most days will be at least 18 degrees with Thursday's top likely to nudge 20 degrees.

According to a global forecast provided by the Canadian meteorological service, south-eastern Australia can expect below-average temperatures for the week beginning August 4:

Another notable feature of July for Sydney has been prevailing westerly winds, leading to clearer skies and less rainfall.

On current forecasts, Sydney should be dry until at least next Tuesday.

Sydney's rainfall this month has been 47 millimetres, or just under half the average for the month.

Australia as a whole is in for a mostly dry week, with the exception of parts of south-western WA where good rain is expected, while western Tasmania will also be particularly wet, according to the Bureau of Meteorology.

The pattern of cold fronts will extend well into August although it is unlikely that they will match the trio of fronts in mid-July that helped set up the cool patch over south-eastern Australia.

"It doesn't look like it will change much in the coming week," Mr Dutschke said. "We can expect to get fairly frequent cold surges [for August] and most won't bring a lot of rain."

Ski fields, though, will fare better, with cold conditions helping to retain the snow and enough regular top-ups to keep conditions good, Mr Dutschke said.

Darwin oddity

July has also brought some other odd events, such as a relative chill in Darwin when the cold air pierced far into the tropics.

The maximum of 33.6 degrees for the city on July 12 was followed by a relatively cool 29 degrees the next day, the largest two-day drop for the month in about 70 years of records, Mr Dutschke said.

For those wondering how southern Australia might be cold during an El Nino period, Mr Dutschke said such events tend not to have an impact on this region until late winter or early spring.

"In recent years, it's warmed quite rapidly in August and it could happen this year, especially as the effects of the El Nino kick in," he said.

The El Nino involves the central and eastern Pacific warming relative to the west, leading to shifting rainfall patterns and a jump in global temperatures. This year's event may also be a big one.

Combined with the background warming from climate change, June and the first six months of 2015 are the hottest on record, a US agency said earlier this month.

Weatherzone is owned by Fairfax Media, publisher of this website