The Bureau of Metereology has forecast rain and thunderstorms from Thursday to Saturday, with possible showers from Sunday to Tuesday. The rainfall predictions range from 5-15mm on Thursday, to 10-30mm on Friday, and 6-25mm on Saturday.

Temperatures are also set to drop from Thursday, with no days expected to surpass 35 degrees.

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Tamworth and Region Weather's David Farrenden said the huge changes were due to a trough in the west, which was "expected to draw in large amounts of tropical moisture".

"This will cause showers and storms across the entire region. Models are starting to firm, with a reasonable chance of 20-50mm on the slopes, upper Hunter and ranges," Mr Farrenden said.

"Even areas of the plains won't miss out with 10-40mm possible from Wednesday to Saturday."

He said rain could even continue into next week.

"As we head into next week there is second trough that could deliver even more storms to the region. However this is not completely locked in as yet," he said.

"We will continue to monitor models for changes."