Ahead of today's all-important qualifying session the air temperature is 16 degrees C, while the track temperature is 22 degrees.

In the two hours since the end of free practice the weather has changed almost constantly and it is likely that there will be further downpours during this session. That said, it is currently quite bright with the sun shining down however, as we know from experience, all that can change very quickly… and usually does.

While Fernando Alonso topped the timesheets in both of yesterday's sessions it was Mark Webber who led the way this morning. That said, due to the constantly changing conditions it has been almost impossible to get a line on who's hot and who's not thus far, and in all honesty that looks likely to continue, especially if the weather gods continue to play games with us.

Ferrari looks good, so do McLaren - despite the (relative) lack of updates. And while Red Bull are playing down their chances here and at Monza, both Webber and Vettel look hungry. Then there's Renault with its raft of updates - astonishing when you think they've only had one week in which to build them - and Adrian Sutil looking very, very good in the force India.

Mercedes will surely be hoping for rain - especially Schumacher who forfeits ten grid places following his silliness in Germany - while Williams and Sauber are both looking good to add a few more points to their tallies this weekend.

Talking of penalties, Nico Rosberg will forfeit five grid places tomorrow after his team opted to change the gearbox on his Mercedes.

Minutes before the session gets underway, Petrov is told that rain is expected halfway through.

The Virgin duo head the queue at the end of the pitlane, a queue that includes most of the big guns, wisely eager to get in a 'banker lap'. Surprisingly, Button is on the option tyre.

On hit out lap Petrov runs over the kerb and spins off into the barriers just after Rivage, his session is over almost before it has begun. The session is red-flagged as the marshals remove the Russian's car.

The session resumes at 14:08 with everyone switching to options, Button having effectively wasted the set he was originally using.

As the queue waits at the end of the pitlane - headed by a Toro Rosso - the rain is clearly moving in. Red Bull are the last team to release their cars.

Halfway through the out lap rain is already falling on the far side of the track. As the drivers jostle for position, Schumacher loses out to Trulli… it's almost like a race.

There's chaos at Stavelot as the rain falls harder, several cars running wide and di Grassi spinning.

With the drivers only likely to get in one hot lap, it's a mad scramble. After the first flying lap Hamilton is quickest (1:56.706) ahead of Button and Massa. Vettel can only manage seventeenth, the German suffering due to his cold tyres.

As the rain continues to fall, only one section of the track, the timing screens don't shown any significant improvements. Vettel could be the real loser here.