Ahead of today's free practice session the air temperature is 13 degrees C, while the track temperature is 16 degrees. It is cool and bright and while there wasn't too much overnight rain the track is still damp. Furthermore, despite the sun breaking through in places there are some nasty threatening clouds in the distance.

Ferrari's Fernando Alonso topped the timesheets in both of yesterday's sessions however, the ever changing weather conditions - not to mention a handful of errant spectators - meant we still don't know the true running order here.

As previously reported, Red Bull passed the revised FIA flex test last night, therefore - weather permitting - we should see the Milton Keynes outfit play its hand today. That is true also of Renault, undoubtedly the most heavily revised car over the summer break and now featuring the French manufacturer's own version of the F-duct.

Tyre choices this weekend are hard (prime) and soft (option). However, it was mostly the full wets and intermediates that were used, especially in the first session.

The lights go green and Jarno Trulli leads Kobayashi, Yamamoto, Petrov, Kubica, Alguersuari and Buemi down the pitlane.

Five minutes into the session everyone has been out for an installation lap as it revealed that there is a 95 percent chance of rain during qualifying this afternoon.

Eleven minutes into the session di Grassi breaks the deadlock, followed, moments later, by Schumacher who is on dry tyres.

Di Grassi crosses the line at 1:56.585 however, moments later Schumacher posts 23.027, the German having been told that his F-duct is working perfectly. A 50.108 sees Buemi go quickest.

As Hulkenberg goes quickest in S2, Hamilton goes quickest in S1. Hulkenberg posts 48.491 to go quickest but moments later a 48.096 sees the 2008 world champion go top of the pile.

On his first flying lap, Vettel can only manage fifth (49.214), the onboard camera showing the German taking Eau Rouge one-handed as he uses his left hand for the F-duct slot.

Hulkenberg re-takes the top spot with a 47.564 only to be leapfrogged by fellow Germans Vettel and then Sutil (47.472).

Twenty minutes into the session, Alonso and Rosberg leave the pits, Massa and Webber still to make an appearance - other than their installation lap.

Having gone quickest in the final two sectors, Kubica goes quickest with a 46.492. Both Saubers now in the top six - de la Rosa using the last of his allotted eight engines here this weekend.

On his first flying lap Alonso goes eighth (47.697) as Hamilton goes quickest with a 46.315. Elsewhere, Webber and Massa are now on track.

As Alonso improves to third, it is revealed that rain is expected within the next fifteen minutes. Massa goes third (46.962) and Webber sixth. All but Liuzzi have now posted times.

Aware of the impending change in the weather, a few drivers - most notably the Renault duo - switch to the option tyres.

At half-time, it's: Hamilton, Kubica, Webber, Alonso, Massa, Vettel, Button, Hulkenberg, Sutil and Petrov.

Having gone quickest in S2 - Red Bull's strongest sector - Webber has a poor S3 and can only manage second (46.440). Next time around the world championship leader goes quickest, crossing the line at 46.106.

Liuzzi finally leaves the pits, Force India having opted to reconfigure the aero package on his car, even to the extent of removing the F-duct.

As a number of very clouds move in, Schumacher is currently twenty-third of the twenty-three drivers who have posted times. With Sutil looking good in the previous sessions we are looking for an improvement from Liuzzi.

Button improves to fourth with a 46.397 having gone quickest in S2. Elsewhere, teammate Hamilton goes quickest in S1. As Liuzzi goes eighteenth, Schumacher improves to fourteenth.

Vettel grinds to a halt as he enters the pits - his car seeming to have lost all power. His crew waits anxiously in the pitlane like worker bees waiting for the queen. Replay suggests a hydraulics problem however, the team subsequently claims that it was an "air box issue".