The territory could be drenched by up to 100 millimetres of rain in the next week as the stormy weather continues.
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The new year is off to a stickier than normal start with humidity akin to late summer already settling in.
Weatherzone meteorologist Brett Dutschke said there was about a 40 per cent chance of a thunderstorm Wednesday afternoon, but thunder and lightning were less likely on Thursday.
But there's a greater chance of stormy conditions on Friday - about 60 per cent - with the bulk of rainfall forecast for the weekend.
Mr Dutschke said thunderstorms in the next few days had the potential to be severe with possible minor flash flooding.
"They look like they'll favour the high country; in Canberra city itself they may not be so likely than in the mountains around it," he said.
"On Saturday and Sunday storms will turn into just rain - we're likely to get significant rain over the weekend. It will be widespread rain in excess of 20 millimetres but there's a chance it will get to more than 100 millimetres [across the ACT from Friday to Sunday]."
The forecast follows two days of thunderstorms at the beginning of the week.
The Bureau of Meteorology issued two severe thunderstorm warnings for the ACT and parts of NSW on Sunday and Monday with rain, thunder and lightning pelting the capital.
Mr Dutschke said the wet weather was more typical of late summer.
"Last year was a much drier summer overall, in terms of humidity at least. It wouldn't happen every summer, anyway," he said.
"We've had north-easterly winds everyday since late last week which have been drawing in moisture from the Pacific Ocean. That moisture brings in the higher humidity.
"Looking at this weekend, there's also moisture coming in from the north and north west. It's about as humid as it will get."
Temperatures in the low-30s are forecast for the next few days before a slight reprieve on Sunday.
Canberrans may be in for some restless nights, with temperatures hovering around 20 degrees as late as midnight.
"It's going to be quite humid," Mr Dutschke said.
"There's some pretty sticky nights not conducive to getting a good night's sleep.
"Sunday is looking likely to be the wettest and coolest day."
