SCotland's largest music festival, T in the Park, this weekend celebrates its 20th year, attracting up to 85,000 music fans a day to the three-day event in Kinross-shire.

The site itself may have mushroomed from its first three outings in the cramped Palace Grounds of Hamilton, but one thing will never change about T in the Park: the unpredictable weather.

As anyone who watched last night's BBC 2 documentary T at 20 will know, the vagaries of the climate help determine the success of the festival as much as the quality of the headliners – this year it is Mumford & Sons, Rihanna and The Killers, among others.

Perhaps it is fitting that Antipodean folk-rockers Crowded House were among the acts in the festival's debut year in 1994, when a rain-soaked and sunburnt audience lifted their voices in unison for the chorus of Four Seasons in One Day.

From Kylie Minogue causing a stampede on the signing tent in 1995 to Hollywood heart-throb Keanu Reeves taking a bus to Strathclyde Park to perform with his band Dogstar in 1996, the extravaganza has never been short of talking points even in its humble Lanarkshire beginnings.

On upscaling to the former Balado airfield in 1997, the festival went on to earn a reputation as Scotland's answer to Glastonbury or Reading.

"The event has constantly evolved," festival director Geoff Ellis said. "We're not an event where we've said there's our fans in '94 and we'll keep those fans all the way along the journey. If we keep some of them, then great, but it's about getting new fans in each year.

"You've got to keep the festival fresh; keep it at the cutting-edge of music. That doesn't mean to say you only do new bands, but you've got to keep it fresh."

The festival took root in the early 1990s when Stuart Clumpus, founder of DF Concerts, approached Tennent's Lager, already sponsors of the Tennent's Live music series, with a view to creating Scotland's first large-scale, multi-stage music event.

The event has now sold more than 2.5m tickets over the course of its 20 years, and was named Festival of the Year by Music Week Awards in 2011.

Tickets for the 2010 event sold out in 90 minutes, although this year's briefs, priced at £82.50 for a weekend day pass, are still available, a fact organisers have attributed to the economy and fans waiting for an agreeable weather forecast.

Its 20th year is being marked with twice as many fireworks as last year, and the arrival of the Arcadia Afterburner, a fire-breathing new addition to the Sunset Strip entertainment zone.

l T in the Park, Balado, Kinross-shire, Friday–Sunday.