Mark Webber celebrated his 35th birthday, and the signing of a new Red Bull Racing contract, by topping the free practice times for a second day at Spa-Francorchamps, but the Australian will know that a repeat of the wet conditions in qualifying could make the grid a lottery.
After an early downpour severely limited running at the start of the hour, an slight improvement in the conditions eventually meant that intermediates could be fitted, and Webber moved to the head of the times with a 2min 08.988secs lap, over 18secs slower than he had managed in Friday's afternoon session. The Australian was closely followed by McLaren's Lewis Hamilton who, along with team-mate Jenson Button, limited his running to the very end of the hour after a lone installation lap early on saw him aquaplaning on the straights.
Hamilton ended the session just 0.054secs behind Webber, but the conditions ensured that the order behind the top two remained unexpected, with Jaime Alguersuari keeping early pacesetters Toro Rosso at the sharp end in third place, ahead of Button, world champion Sebastian Vettel and STR team-mate Sebastian Buemi. Nico Rosberg, who suffered a right-front puncture shortly after fitting inters, wound up in seventh spot, ahead of Adrian Sutil, Bruno Senna - now definitely hoping for the rain to continue all weekend - Michael Schumacher and Paul di Resta, the Scot among those to explore the recently tarmac'd run-off areas during the hour.
Also appearing higher than usual in the order, Heikki Kovalainen was eleventh for Team Lotus, while Jerome d'Ambrosio broke the top 20 after being the first man out on his home circuit.
Ferrari, in direct contrast to their frontrunning rivals, appeared content to keep their powder - and tyres - dry, with Fernando Alonso not even setting a time during five tentative laps. Team-mate Felipe Massa completed only a couple more laps, and wound up 23rd as a result, fully 13secs off Webber's pace.