Widespread thunderstorms are forecast to develop on Sunday and Monday over the ACT and a large area of southern NSW.

In a severe weather warning, the Bureau of Meteorology says a strong cold front in western NSW on Saturday night will move into the central parts of the state early Sunday morning and combine with elevated moisture feeding into the area from the north.

BoM says heavy rainfall that may lead to flash flooding is forecast with areas of rain and thunderstorms for the southeast of NSW from Sunday morning.

“Six-hourly rainfall totals of 30 to 60 mm are likely, with isolated totals up to 80 mm possible over alpine peaks. 24-hourly rainfall totals of 60 to 80 mm are likely, with isolated falls of 120 mm possible, mainly near the Victorian border,” BoM warns.

Heavy rainfall and damaging winds are forecast to ease below warning thresholds late Sunday afternoon or evening.

Meanwhile, the NSW State Emergency Service (SES) is warning of potentially intense heavy rainfall, saying residents should also prepare for widespread damaging wind gusts exceeding 90km/h and potentially destructive wind gusts over 125 km/h.

The storms will also pose a risk of heavy to locally intense rainfall, leading to flash flooding and local river rises.

NSW SES State Duty Commander, Assistant Commissioner Colin Malone said it was time for residents to prepare now.

“Ahead of the thunderstorm risk tomorrow, you should take time to prepare your homes,” he said.

“Loose items in your yard can be thrown around during strong winds and cause damage to property and injury to people.

“Put away anything you can and be sure to trim branches and trees away from your property.

“Never park your car under trees or powerlines, and if intense rainfall develops in your area avoid driving.

“Flash flooding is also a big concern with these storms – it can occur very quickly and without official warning.

“If you come across a flooded road please make a safe decision and turn around, find an alternative route it is just not worth the risk”