Ahead of this afternoon's session, the air temperature is 22 degrees C, while the track temperature is 21 degrees. There was a heavy downpour right after this morning's session, the sky turning black at one stage. However, for the last hour there has been no further rain and the track appears mostly dry.

Due to the ever changing conditions, on various parts of the track, this morning's session was pretty much inconclusive, no disrespect to Mercedes duo Michael Schumacher and Nico Rosberg. That said, at this stage we are expecting similar conditions for the remainder of the weekend.

When the lights go green Kobayashi leads the way, followed by Ricciardo, d'Ambrosio, Perez and Buemi. The sun is shining but there is an ominous dark cloud on the other side of the track.

Following his crash this morning, Force India has opted to change the gearbox on di Resta's car, though they stress that this is purely a precautionary move.

There is still lots of spray, especially in Fagnes section of the track.

Kobayashi gets things underway with a 2:16.279, demonstrating that conditions are still far from ideal, a point amply demonstrated by Schumacher who makes a mistake and runs wide.

Webber posts 2:11.652 to take the top spot, the Red Bull driver going quickest in all three sectors. Most drivers are on inters though Schumacher is on full wets.

Webber improves again, the Australian posting 2:10.524 as Alonso goes second with a 2:10.839.

Senna makes up for this morning's mishap when he goes third with a 2:10.901, as Webber continues to set the pace, the Australian now down to 2:08.351.

No sooner has Senna improved to second (2:09.558) than Petrov makes it a Renault 2-3 courtesy of a 2:08.889.

Eighteen minutes into the session there are 19 names on the timesheets, Perez, Button, Massa, Hamilton and di Resta the only drivers yet to post a time.

On his first flying lap Vettel goes quickest (2:06.398) as Alguersuari goes second ahead of Senna.

Buemi posts 2:05.719 but moments later Alonso goes quickest in all three sectors, finally crossing the line at 2:03.953. Button, who had gone quickest in S2, opts to abort his lap in the final sector.

With Massa, Hamilton and di Resta yet to post a time, Button edges ever closer to the two-minute mark, the McLaren driver posting a 2:02.206. Hulkenberg, who is standing in for Sutil in this session, goes second with a 2:03.852.

The overhead shot shows a dry line for much of the track now, as Schumacher posts 2:03.549 to go second.

As Barrichello, sporting that unusual new rear wing, seeks to improve on nineteenth, Buemi is told that rain is expected within the next fifteen minutes. Barrichello subsequently improves to eighth with a 2:04.188.

Webber ups the ante with a 2:01.015 as the dark cloud close in. Rosberg takes second with a 2:01.741 as Webber improves yet again (2:00.964).

Despite the threat of rain, Alonso is the first driver to make the switch to medium (dry) tyres. It's a brave move as Ferrari seeks to obtain some data.

The Spaniard is 0.5s up in the first sector and 2.986 by the second split. As he crosses the line at 1:56.292 it is sure to start a mad scramble in his rivals' garages.

As Alonso improves in the first sector of his next lap, Hamilton leaves the pits on a set of mediums. The McLaren driver subsequently complains of vibrations.

A 53.186 sees Schumacher (soft) go quickest only to be leapfrogged by Alonso moments later with his 53.942.

Next time around, Schumacher, making full use of his DRS through Blanchimont, retakes the top spot with a 52.102.

Tremendous super-slow-mo shot of Hamilton at La Source, his front brakes glowing red hot.

Rosberg (soft) makes it a Mercedes 1-2 when he posts 51.967 to go quickest. Hamilton goes fourth with a 52.800.