A deepening low pressure system threatening heavy rains in the west of NSW is expected to worsen flood conditions as it moves towards the coast.
Australia is on track for its wettest spring in a decade and some regions in NSW have already received more than three times their normal rainfall for November.
NSW Farmers is calling for natural disaster declarations to allow relief funds as the rain continues, destroying crops and causing widespread flood damage.
The lower west and Riverina regions have been warned of heavy rainfall with "a complex low pressure system" near the border with South Australia.
That slow-moving system is expected to deepen before moving towards the coast on Thursday evening.
The heavy rain could spark flash flooding, with forecast six-hourly rainfall totals between 40mm and 60mm.
Severe and "near stationary" thunderstorms were also looming over the south coast and southern tablelands on Thursday afternoon.
Already on Thursday some areas have copped a drenching, with a rain station south of Griffith measuring 60mm in an hour.
Snowball, southeast of Canberra, recorded 28mm in an hour and Braidwood recorded 15mm in 30 minutes.
Areas including Coombah, Hay, Wilcannia, Broken Hill, Ivanhoe, Menindee and Balranald are in the path and Sydney's Warragamba Dam received 96mm of rain in 24 hours.
NSW Farmers Grains Committee chair Justin Everitt said members were reporting paddocks under water, with the focus moving from saving the harvest to minimising damage to the land.
"It is cruel for our growers to watch these amazing crops - this potential income after so many years of drought - drowned before they could be harvested," he said.
"We urgently need a range of measures to help people start to clean up and get on with their lives."
Natural disaster declarations would allow government grants and concessional loans, while additional support for local government would be needed to repair damaged roads.
Flooding has closed the Barrier Highway west of Broken Hill with water over the road at Cockburn, on the South Australian side of the border.
The Kamilaroi Highway between Gunnedah and Boggabri has also been closed by flooding, as has the Cobb Highway between Ivanhoe and Wilcannia.
Lachlan Valley Way, Henry Lawson Way and New Grenfell Road between Forbes and Gooloogong have all been closed by flooding too.
There has been some good news in Forbes, where all the people ordered to evacuate last week have been given the all-clear to go home.
Flood risks remain with further rain forecast and the SES has warned returning residents to stay prepared in case they have to evacuate again.
Damaging winds have also been predicted for alpine areas of NSW, with peak gusts of more than 125km/h possible in areas including Braidwood, Charlotte Pass, Thredbo, Cabramurra, Selwyn and Khancoban.
Weather bureau head of operational climate services Andrew Watkins says the summer outlook for NSW is wet, with temperatures cooler than usual on the coast and warmer than usual in the state's west.
Daily minimum temperatures are expected to be higher than normal as increased cloud traps hot air, leading to warmer nights.
The areas where flooding is a renewed risk include the Belubula, Hunter, Macintyre, Macquarie, Peel, Castlereagh, Bell, Tumut, Murrumbidgee, Snowy and Tumut rivers.
The Lachlan and Namoi rivers remain at risk of flooding and there are warnings for the Severn, Gwydir and Paroo rivers.
The SES has expanded its area of operations in an effort to mitigate flash-flooding risks, having already rescued people from the roofs of their cars after they tried to cross floodwaters.
Australian Associated Press
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