The BoM is expected to announce on Tuesday that Australia is in a La Nina weather pattern. The phenomenon typically increases the chance of above average rainfall across much of Australia during spring and early summer.

Local NSW Farmers' branch chairman Kevin Tongue said rain during the first harvest in years could cost growers real money.

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"It'll cost money to people if the crop is downgraded. From say a malt barley to a feed two or something like that there's probably $40 a tonne difference in the price of it," he said.

"Wheat would be similar in value that it loses if it gets weather damage.

"Plus it's just a pain in the neck to harvest on wet paddocks with trucks and chaser bins and headers and things like that. it is a concern if we got a big fall of rain."

The Bureau of Metereology says the city has an 80 per cent chance of above average rainfall.

There is a 75 chance of 200 mm of rain over the three months to December, according to the BoM's latest climate outlook.

It comes on top of months of solid rainfall. Tamworth dams are gradually filling up, with Chaffey and Split Rock dams now at 26.1 per cent and 4.9 per cent full.

Mr Tongue said farmers welcome more rain, and a light sprinkling of rain probably wouldn't been too difficult to handle. But a heavy rainfall could see farmers disappointed, he said.

"The last thing we want's a wet harvest. We've been waiting so long for this crop. If it gets downgraded that's less money that we make from it. It's a bit of a concern."

Nights during October to December are very likely to be warmer than average across the region. But days are set to be relatively mild, and are likely not to exceed the average maximum temperature regularly in Tamworth.

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