Up to 50 millimetres of rain could hit Sydney as heavy downpours make their way to the coast tonight after giving parts of the west a much needed drink.

Key points: Drought-stricken NSW farmers celebrating as heavy rain sweeps across the state

Drought-stricken NSW farmers celebrating as heavy rain sweeps across the state Broken Hill receives 34.2mm overnight — double the amount reported for the whole year

Broken Hill receives 34.2mm overnight — double the amount reported for the whole year Today kicks off four days of rain set to hit NSW

Heavy rain is expected to intensify on the coast at about 10.00pm and flash flooding may occur in Sydney and the Central Coast tonight and early tomorrow.

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A severe weather warning is in place and the downpour is expected to bring in over 50mm of rain over a 12-hour period, with some localised totals exceeding 100mm.

The BOM is predicting the rain will affect areas including Gosford, Sydney, Parramatta, Wyong, The Entrance and Woy Woy.

Some of the state's west had its thirst quenched earlier today which has been a cause for celebration for farmers.

Broken Hill recorded 34.2mm — double the amount reported for the whole year — and towns like Dubbo, Menindee, Ivanhoe and Orange all saw significant rain.



Tim Neville from Blantyre station, 90km east of Menindee, said he was overjoyed after recording more than 40mm if rain at his station.

"It was a beautiful drop of rain," he said.

"I've been following the weather pretty hard lately, just hoping for every bit that they say you might get just five or ten millimetres or whatever.

"But yeah, it's bloody great to see, I'm just lost for words."

The thunderstorm also triggered a huge dust cloud in Broken Hill and other parts of the far west last night, causing the skies to turn red.

Retired forecaster and Broken Hill resident Phillip Mew said it was the strong winds that turned up the dirt.

"Because the ground is so dry you get down drafts from these actual clouds," he said.

"It created the dust storms that ripped through Broken Hill."

Today is the start of four days of significant rain for Sydney and NSW, with the state still in the midst of crippling drought.

Sorry, this video has expired Dust storm hits Broken Hill

When is a drought finished?

The NSW Government in August declared that 100 per cent of the state is in drought.

That status has continued into this month, with the State Government already announcing more than $1 billion in drought relief measures.

The state's Department of Primary Industries determines drought status based on data from the BOM.

Generally a drought-breaking event would be "three or four" significant rain days in close succession, it said.