V8 Supercars championship contender Mark Winterbottom says forecast rain will make qualifying for Saturday's 300km race on the Gold Coast more crucial than ever.

Afternoon showers and even a possible thunderstorm are expected to hit the Surfers Paradise street circuit, opening up the possibility of a chaotic race in the concrete-lined track.

Winterbottom, a two-time winner on the Gold Coast, needs a solid result in this event to close the 188-point gap to championship leader Jamie Whincup.

He showed he has the pace to qualify up near the front after clocking the second-fastest time in Friday's practice run behind Holden's Michael Caruso, but the Ford star was in no doubt about the importance of maximising track position in the morning qualifying run.

"Definitely, you've got to put it in a good position and more so here than anywhere else," Winterbottom said.

"If it's wet and you're 10 deep in the pack, visibility is going to be shocking and it's going to be tough.

"If it's a dry race, pole's important. If it's wet, pole's probably more important because you get clean of all the stuff that's going to go on."

Winterbottom, Whincup and their other title rivals - Craig Lowndes and Will Davison - are the only drivers to have won a race in 2012 but Caruso feels he's not far off breaking into that exclusive club.

The Garry Rogers Motorsport driver said he was feeling confident after a string of recent good performances.

"The last few rounds we've been right there in the mix," Caruso said.

"It's nice to be at the pointy end and I think we're not far away. A lot of hard work paying off is what you're seeing today."

Bathurst runner-up David Reynolds continued his hot form by posting the third-fastest time in Friday's practice while Whincup was fifth quickest and Lowndes could only post the day's 10th fastest lap.

Saturday's action begins with qualifying and a top 10 shootout for pole from 9.35am AEST before the 300km race starts at 1.40pm (AEST).