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Campers due to start arriving at T in the Park later are being warned to take the wellies and waterproofs with predictions of rain, hail and lightening over the weekend.
The campsite at Ballado opens today but performers wont be on stage until tomrrow night.
Tens of thousands of music lovers will flock to the three day event to see stars including Beyonce, Coldplay and the Tinie Tempah.
Other performers include The Saturdays, N Dubz and Scotland's homegrown star Calvin Harris.
Crowds of up to 85,000 are expected at the extravaganza which runs from tomorrow to Sunday at Balado near Kinross.
This evening they can enjoy the first public premiere of You Instead, which was filmed at T in the Park last year.
Directed by David Mackenzie it is a love story set against the backdrop of the festival.
Tayside Police said the Citizen T initiative launched last year will continue for the 2011 festival.
It encourages positive community behaviour, including looking out for friends and fellow campers, binning litter, taking your tent home at the end of the weekend and having fun while staying safe.
Forecasters predict heavy, slow-moving showers and possible hail storms for the area today.
The wet weather is expected to continue tomorrow and at the weekend, broken by sunny intervals.
Brendan Jones, a forecaster with Meteogroup, the weather forecasting arm of the Press Association, said: "Every day there will be heavy downpours to contend with and the possibility of gusty winds, hail and lightning.''