According to the Wagga Bureau of Meteorology station's technical officer Nigel Smedley, the freeze will sneak up from below.

"The cold front will gradually approach the state from the south today, and will cross the western and southern districts Tuesday, bringing significantly cooler conditions," he said.

Following the cold snap will be a broad low pressure system originating in South Australia.

"That system will move slowly across NSW from South Australia starting Thursday, bringing showers and possible storms to most districts," Mr Smedley said.

Temperatures are forecast to drop well below average in the days to come, according to Mr Smedley, who said could fall below zero.

"A normal average for this time of year is 14.5 degrees during the day and 3.5 at night, but Tuesday is set for a minimum of 3 degrees and maximum of 11," he said.

"It gets even colder Wednesday, with minus two overnight and 11 during the day."

Thursday is also forecast to have a minimum temperature of -2 degrees and a maximum of 11, followed by a low of 3 degrees and top of 11 degrees on Friday.

Rain is also on its way, with Friday forecast to see a 90 per cent chance of 10-20mils, and a 90 per cent chance of 4-10mils on Saturday.

"It's looking to warm up a little on Sunday though with a 5 degree minimum and top of 14 degrees," Mr Smedley said.