SPA-FRANCORCHAMPS, Belgium (AP): Mark Webber was fastest for a third straight practice session at the Belgian Grand Prix as drivers faced mixed weather conditions on Saturday before qualifying.
The overall F1 leader took advantage of dry, sunny conditions to steer his Red Bull around the Spa circuit in 1 minute, 46.106 seconds before a sprinkling of rain fell on the track.
The leading times were identical to the order of the four leading drivers in the championship standings, with McLaren driver Lewis Hamilton closest to the Australian in a time of 1:46.223.
Sebastian Vettel of Red Bull was third in 1:46.396 ahead of McLaren counterpart Jenson Button, who was just under three-tenths of a second behind Webber.
Fernando Alonso of Ferrari was sixth - just over half a second back - before conditions worsened to leave the five leading title contenders with more time in the garage than on the track.
Webber leads Hamilton by four points in the standings with 161, while Vettel is third with 151. Button has 147 points and Alonso 141. Webber has won two of the last three races while Red Bull has taken pole in 11 of 12 races so far.
However, the variable weather could throw up a surprise with the conditions over the Ardennes countryside circuit constantly changing.
With only three sets of extreme wet tires for the entire weekend, teams preferred to save them for qualifying and Sunday's 44-lap race than to use them in the final practice session.
Ferrari has won three straight Belgian GPs and five of the last seven. Ferrari and McLaren have won every race but one here since 1996 - the exception being Damon Hill's victory with Jordan in 1998.
Robert Kubica continued to enjoy Renault's new F-duct aerodynamic system as the Polish driver was fifth fastest in the 60-minute session.