About 12mm of rain fell on Canberra on Monday evening from about 5pm bringing Canberra's total rainfall for the month to 34.8mm, still well below the August average.

The ACT's showers were light though compared to some areas of NSW, which saw hail and storms dropping up to 100mm of rain throughout the state's south-east.

Three people had to be winched to safety from a flooded creek west of Moruya on Tuesday morning, after their four-wheel-drive became bogged.

The Bureau of Meteorology's Katarina Kovacevic said the heavy rain had been caused by the interaction of two strong weather formations.

"We've got what we called an upper-level cold pool and a coastal surface trough, and the two of those combine to give atmospheric instability which causes rain," she said.

But Ms Kovacevic said the rest of August should be fairly dry for the ACT, as the cold pool moved north easing rainfall in south-east NSW.

"On Wednesday we're expecting a dry day, so no rainfall, and after a cloudy start we should see a mostly sunny day," she said.

"There's a small chance of precipitation on Saturday, a very small chance, but otherwise Canberra will be dry to the end of the month."

As the rain disappears, the day's are expected to heat up in the ACT, with temperatures slowly building during the week to a top of 18 degrees on Sunday.

But the clear skies and light winds will come at a cost for Canberrans - the nights are forecast to drop back below zero from Thursday.

"If there's no cloud at night, the ground radiates energy away and you get cool nights," Ms Kovacevic said.

"But clear skies during the day means it is sunny and so the sun warms the earth,"