Thunderstorms are expected to hit Thursday afternoon and into the evening, continuing overnight in some areas.

Locations which may be affected include Dubbo, Nyngan, Narromine, Bourke, Parkes and Orange.

It is predicted there will be localised heavy rainfall with flash flooding also possible throughout.

Large hail and damaging winds are more likely in the west and south.

Dubbo is expected to experience light winds becoming northerly 20 to 25 kilometres per hour in the middle of the day then becoming light in the early afternoon.

Northwest to northwesterly winds in the Narromine Shire are expected to reach up to 30 km/h tending east to northeasterly about 20 km/h in the late evening.

Forecaster for the Bureau of Meteorology Abrar Shabren said rainfall totals would vary across the state due to the heat and nature of the thunderstorms.

"Looking ahead in the next couple of days, particularly on Thursday we're looking at a trough deepening and associated with that there will be a frontal moving across the state as well," he said.

"That trough is bringing quite an unsettled weather phenomenon across NSW."

Mr Shabren said we would see thunderstorm activity across the state in many places, and most of the rainfall would be from thunderstorm conductivity.

"At this stage over the four day period from Thursday to Sunday, widespread totals will be about 80 to 50 millimetres, but that's more to the south," he said.

"Around the Central West Slopes and Plains you might see a little bit more 80 to 60 millimetres, but isolated falls could be heavier as well.

"Towards the western side Nyngan and Condobolin will get a little less, Forbes Parkes Wellington, Narromine Dubbo and Coonabarabran all these places will get a little more from the thunderstorms, or thunderstorm activity will be quite more pronounced."

For emergency help in floods and storms, ring the SES (NSW and ACT) on 132 500.