"Compared to the last few days where it was 20 degrees, the next six days will be seven to eight degrees cooler right through until Sunday," Weatherzone meteorologist Brett Dutschke said.

Early risers will need a scarf with the temperature to begin at minus two on Wednesday and minus three on Thursday.

There's a slim chance that on Thursday and Sunday that Leeton may actually reach its August average temperature of 16 degrees Celsius.

It's expected to be cold, dry and breezy with significant windchill.

It's not all bad news however, as Mr Dutschke said the entire region could receive its annual August rainfall between Thursday night and the weekend.

A slow moving low pressure system is arriving in the MIA from the west and is expected to interact with tropical moisture from the north.

"You've got a lot of moisture coming from the north, and the low pressure system will be at its most intense over far western NSW," he said.

The rain is forecast to begin Thursday night.

"Friday is easily likely to be the wettest day with the potential for heavy, soaking rain," Mr Dutschke said.

Around 30 to 50 millimetres is forecast starting in the north-west with Rankin Springs, Hillston, Lake Cargelligo and Goolgowi before arriving in Griffith.

Scattered showers are predicted for Griffith over the weekend while Leeton, Yanco and Narrandera are expected to receive around five millimetres on Saturday before Ardlethan, Temora and Coolamon receive rain on Sunday.

"The whole region will pick up its monthly average. It should do it by the end of the weekend, if not in 24 hours," Mr Dutschke said.

"There's a chance of similar weather coming by the end of the month," he said.

Mr Dutschke said it appeared the weather pattern had shifted to increased chances of rain.

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