Sydney is on track to post its fourth warmest December on record, according to Weatherzone. For the year, the city's mean, maximum and minimum temperatures will be in the top five warmest on records going back to 1858, the Bureau of Meteorology said.

For Melbourne, very warm spells in March and November will likely place the city among its 10 hottest years for maximums.

Most of the nation will post another year above average - with Sydney notching its 25th in a row - as warming from climate change gradually bumps background temperatures higher regardless of the fluctuating influences of El Nino and La Nina events.

"2017 will be recorded as one of Australia's five warmest years on record, with the national mean temperature between 0.8 and 0.9 degrees warmer than the mid-20th century average," Karl Braganza, head of climate monitoring at the bureau, said.

"This happened despite the absence of an El Nino in the Pacific, which is normally associated with very much warmer than average conditions over Australia."

While international media might be focused this week on the break-out of Arctic chill over much of eastern North America, average land and sea temperatures will rival the past three years of consecutive record annual global temperatures.

With a continent as large as Australia's - and with a naturally varied climate, particularly for rainfall - every year is going to have its contrasting weather.

For NSW and Victoria, the year was largely one marked with a wet start, a long dry spell in the middle, before a mix of unseasonably warm conditions and some welcomed return of rain.

An unusually quiet cyclone season meant little northern penetration of rain until ex-tropical Cyclone Debbie dumped huge amounts of flooding rains along coastal Queensland and NSW.

The storm did, however, help bring an end to a second highly damaging bout of bleaching to the Great Barrier Reef in as many summers that has left as much as half the corals dead in the worst back-to-back event recorded.

Record heat

It may seem a long time ago, but last summer was Sydney and NSW's hottest, with many records broken and the electricity network brought to the brink of large-scale blackouts in February.

The heat was particularly persistent in north-east NSW, with Moree experiencing 54 consecutive days above 35 degrees - the longest such spell on record anywhere in NSW.

Sydney's reading of 36.5 degrees at 9am on January 18 was the warmest since records for that time of day began in 1955, the bureau said.

Victoria's summer was more moderate, with Melbourne failing to notch a 40-degree day for the first summer since the 2004-05 summer.

Autumn got off to a wet beginning for Sydney, with the city posting its wettest March since 1975 - before the heavens started to dry up. The extra cloud around that month helped give Sydney its hottest March for minimum temperatures on record - as it was also for NSW as a whole.

Sydney went from its wettest March since 1975 to its driest April-May in 11 years. Photo: Peter Rae

Victoria went the other way, setting its second-warmest March on record for maximum temperatures, with the mercury an average of 3 degrees above the norm.

Oddly, both Victoria and Tasmania were warmer in March than the previous month.

Bumper snow

Winter brought its range of alpine treats, with a slow start to the snow season ending up with the best since 2000 for many ski resorts.

By late September, snow depths at Spencers Creek in the Snowy Mountains peaked at 240 centimetres, the deepest at any time of year since 2000, the bureau said. Resorts kept their ski lifts running longer as a result.

Thredbo and other resorts had their best snowfalls since 2000. Photo: Alex Ellinghausen

The good snowfalls, though, weren't matched by rain in many areas. Victoria had its driest June on record, and ended up with its driest winter since 2006.

For NSW, it was the driest winter since 2002, with half the usual rainfall. It was also the state's third-warmest for maximum temperatures.

Early fire season

Spring began somewhat ominously for fire authorities, particularly in NSW, with the state posting its driest September. Sydney's meagre 0.2 millimetres of rain could hardly have been less.

For Victoria, spring was most notable for its heat, coming in as the state's fourth-warmest on record for mean temperatures.

Melbourne (and Tasmania) sweltered in November as a blocking high in the Tasman Sea kept temperatures high in the south of the continent and mild for most of the east coast, including Sydney.

Melbourne's Olympic Park collected 15 days of at least 30 degrees in spring - three more than in the previous record spring of 2009 and almost four times the long-run average of four such days in the season.

The combination of above-average temperatures and rainfall deficiencies had fire authorities bracing for a dangerous season.

Rain reprieve

Decent rain in December, though, helped ease the threat across Victoria, while days of storms have all but eliminated the near-term risk in north-eastern NSW.

"It's a more positive outlook when it's compared to the original fire potential," Ben Shepherd, senior spokesman for the NSW Rural Fire Service, said.

Still, significant rainfall deficiencies exist in the state's west, and for a region stretching from north of Nowra on the coast to Sydney and into the Hunter.

Late spring heat brought people to beaches in Melbourne while Sydney will likely post its fourth-warmest December. Photo: Janie Barrett

Since July, the RFS had dealt with 9200 bush, grass and scrub fires, up from 7700 fires at the same time a year ago, Inspector Shepherd said.

Craig Lapsley, Victoria's Emergency Management Commissioner, said those December rains gave crews a reprieve: "If we didn't have that we'd be in a serious fire season."

So far this year, Victorian authorities have dealt with 2668 fires compared with 4898 for the entire 2016-17 year, he said.

Areas including Warburton, the Yarra Valley and the Dandenongs around Melbourne remain a concern, and another spell of persistent heat could again elevate the fire threat.

"Seven hot days in a row can change the environment dramatically," he said.