Ruawai dairy farmer and former director of Fonterra board Greg Gent said Northland farmers were facing the effects of an $8.40 payout they received in 2014 which earned them $748 million.
"Dairy prices always over and undershoot in terms of their volatility but the biggest issue for Northland dairy farmers is how long will the current prices last?"
He said factors such as climate and exchange rates also played a part in dairy payouts.
When asked how long low prices were expected to last, he said: "The weather is easier to predict than dairy prices."
Mr Gent expects the revised forecast for next season to be in the low $4s. He said another low payout could pave the way for small-scale dairy farmers in Northland to exit the industry.
Federated Farmers Northland dairy chairman Ashley Cullen said he would be "very surprised" if next season's payout forecast exceeded $4.
"Sadly prices at the auction haven't reached the bottom yet and, after Friday, there'll be a lot of soul searching as to what farmers are going to do next.
"Farmers will borrow more and put pressure on everyone ... banks, supporting businesses and the like. Some will rear fewer calves and more Friesian bulls because they fetch good prices at the moment," he said.
Mr Cullen, who milks 200 cows on his Maungaturoto farm, said another option for dairy farmers would be to reduce their stock by up to 10 per cent.
In May, Fonterra announced the latest milk price forecast of $4.40 per kg of milk solid for this year - a reduction of 10 cents from its earlier forecast of $4.50 per kg.
The small reduction will slash $356 million in milk money from Northland's economy this year if $4.40 is the final payout next month. Fonterra is blaming the lower forecast to an over-supply of dairy products in world markets.
