The ACT was dampened by 7.6 millimetres of rain to 9am after a three-hour downpour from about 11pm Wednesday brought the heaviest rainfall in about a week.

Weatherzone.com.au meteorologist Tristan Meyers said the wet conditions were caused by a low-pressure trough that was moving east across NSW and had just touched the ACT.

"Most of the rain cleared by Thursday morning but you're still...[getting] patchy showers.

"There will be continued falls for Thursday but they're expected to clear in the evening."

Mr Meyers said Canberra averaged 10 wet days in September with an average monthly rainfall of 52 millimetres.

"It's fairly normal for this time of year," he said.

He said the cloud would break up and bring early morning frost and sunny skies on Friday, with a chilly minimum temperature of 1 degree in the morning warming up to 16 degrees later in the day.

The sunshine would linger on Saturday before clouds gathered again on Sunday and rain fell south of the ACT.