The Bureau of Meteorology issued a flood watch yesterday, reporting that there was a more than 70 per cent chance of moderate to major flooding from today in parts of Queanbeyan and the chance of major flooding in Cooma.

The ''major rainfall event'' unfolding across the region over the next few days meant flooding had the potential to match, or even surpass, the region's 2010 floods, a bureau hydrologist said.

NSW State Emergency Service Queanbeyan spokesman Mitchell Clout said the unit responded to 10 calls for help yesterday. Most of the calls were from people wanting sandbags around their homes.

''We're planning for the worst and hoping for the best,'' Mr Clout said.

''In the planning stages throughout today we have involved NSW Police and the ACT Emergency Services Agency.''

The bureau said torrential rain and thunderstorms posed a significant flood threat to large parts of southern NSW, including the ACT.

More than 35mm of rain was dumped on Tuggeranong between 9.30am and 10.30pm yesterday and ACT SES responded to 35 calls for help from 3pm because minor flooding across Canberra.

Parks and recreation areas near the Murrumbidgee, Molonglo and Queanbeyan Rivers were closed yesterday afternoon, as were several roads in the region.

''Further closures may be necessary due to the predicted heavy rain,'' a Territory and Municipal Services spokesperson said.

Cooma Airport was lashed with more than 25mm of rain and Goulburn, Batemans Bay and Braidwood received a significant dumping.

The bureau's NSW regional director Barry Hanstrum said, ''The heaviest falls are most likely in a band running between Broken Hill to the south and central coast, including Ivanhoe, Forbes, Young, Cowra, Canberra, Goulburn, Wollongong and Sydney.

''Some locations could receive falls in excess of 300mm over the next several days. This event is perhaps the most significant rainfall event that some of these areas have seen in decades and records may be broken.''

The NSW SES commissioner Murray Kear urged people in affected areas to prepare now.

''People living and working along rivers and streams in the areas affected by the Flood Watch and warnings should prepare now,'' Mr Kear said. ''If you live in rural areas lift pumps and relocate livestock and equipment to higher ground.

''If isolation is likely, stock up now on food, fuel, medicine and other essential items.''

Meanwhile, Canberra put itself in the record books yesterday, recording the coldest summer in 16 years, The Weather Channel said.

Its senior meteorologist Tom Saunders said, ''La Nina conditions caused below-average temperatures this summer. The average temperature for the city was 1.1 degree below normal at just 18.7 degrees - two degrees colder than our 2011 summer and more than three degrees colder than our 2010 summer.''

Bureau of Meteorology climatologist Acacia Pepler said Canberra has also had the fewest days above 30 degrees since the summer of 1992. It also has not had any days above 35 degrees this summer. That compares to an average of five days above 35 degrees, Ms Pepler said. The last time there were no days above 35 degrees in summer was in 2002.

La Nina's tend to bring enhanced rainfall and cooler conditions during the summer months, she said.

At 9am yesterday, 202.4mm of rain had fallen on the capital since December 1, well above the historical average of 168.7mm. Last summer 375.2mm was recorded. The summer rainfall record was gazetted in 1948 when 476.9mm of rain fell.