NSW Bureau of Meteorology has issued a severe thunderstorm warning for Lismore.

The warning issued at 7.45pm is for heavy rainfall with slow-moving storms.

In addition the NSW Bureau of Meteorology predicts that Lismore could see between 60mm to 120mm of rain tomorrow.

"A humid easterly airstream is feeding into a pair of low-pressure troughs; one located offshore and another inland. This pattern is bringing unsettled weather across NSW resulting in localised heavy rainfall with thunderstorm activity this evening, extending into the overnight period," the bureau said.

"Severe thunderstorms are likely to produce heavy rainfall that may lead to flash flooding in the warning area over the next several hours. Locations which may be affected include Lismore, Grafton, Coffs Harbour, Armidale, Tenterfield, Tamworth, Gunnedah, Moree, Narrabri, Walgett, Dorrigo and Lightning Ridge."

Almost 30mm of rain had fallen at Lismore Airport in the 12 hours to 9.30pm.

In Lismore, the rainfall will ease on Friday with 6mm to 25mm of rain predicted. There will be a high chance of showers with a chance of a thunderstorm.

The weekend will see up to 1mm of rain on Saturday, and 2mm to 8mm forecast on Sunday.