"This is the seventh time this year we have seen such heavy and widespread rainfall push through inland NSW," weatherzone.com.au meteorologist Martin Palmer said.

The rain is great news for areas that have endured years of drought. Many districts have already exceeded their mean annual rainfall by huge margins.

"Much of inland NSW is at around 80 to 150 per cent of their mean annual rainfall already. This next event will improve these figures considerably," he said.

The rain is pushing through the Upper Western and has already dumped more than 13mm at Tibooburra, the highest for September in 12 years.

A rapidly deepening low is responsible for the coming wet weather.

"A low currently over the interior and South Australia will begin to deepen during Friday and drift east. As it does so, it will push some increasingly heavy rain and storms into NSW."

Today the rain should bring some high totals with as much as 50mm in parts of the Upper Western. But tomorrow, the state will be awash as the low and a trough push through.

"Saturday is going to be the big rain day for much of NSW as the low deepens and the trough pushes through. Heavy rain and storms should move through during the early hours, reaching the Central West and ranges by mid- to late morning," Mr Palmer said.

Widespread 24-hour falls of about 20 to 30mm could occur right across the state, weatherzone.com.au said.

A further 60mm could fall over parts of the Upper Western and 30 to 40mm is possible over the western slopes.

Some of the rain should reach the coast too.

"To some extent, the ranges will dry the air before it hits the east coast, although some good rain should reach Sydney and the catchments with up to 30mm expected."

Winds are also going to be a factor as the deep low swings to the south.

"We could see some very strong and gusty winds push through during Saturday, the worst of which will most likely affect the Southern and Central Tablelands."

Weatherzone.com .au said this could be some of the best early spring rain for some parts in well over a decade.

smh.com.au

Weat herzone.com.au is owned by Fairfax Media.