Ahead of today's sole free practice session, the air temperature is 30 degrees C while the track temperature is 43 degrees. Humidity is 33%.

Though there was some rain yesterday evening, it has been dry ever since. However, there is still talk of rain tomorrow.

With yesterday's morning session compromised by an earlier downpour it was the second session that gave us a better idea of the running order. Lewis Hamilton topped the timesheets - courtesy of a new rear wing - with the Red Bulls and Fernando Alonso in close proximity.

Ahead of this afternoon's qualifying session, over the next hour we should get a much better idea of how things stand as the drivers prepare for the most important race of the 2010 season. It is not only the world championship at stake this weekend, a number of drivers have yet to secure drives and this is effectively their last chance to impress. Indeed, even the pole-man in Brazil, Nico Hulkenberg, has yet to confirm a seat for next year.

Furthermore, there remains the battle of the constructors. While Red Bull has secured the title, let's not forget that the final standings decide who gets what in terms of the all-important prize money. In other words, there's everything to play for right throughout the field.

Trulli leads the way when the lights go green, di Grassi, Heidfeld, Glock, Alguersuari, Petrov and Rosberg follow.

Five minutes into the session, only the McLarens are on track, the other twenty-two drivers each having completed the obligatory installation lap. "I have a vibration," says Hamilton.

Despite the fact that so much depends on this weekend, indeed, this session, there follows one of those interminable periods of total inaction with drivers either chatting to their engineers in the garage, waving to the fans from the pit wall or waiting patiently in their cars.

Di Grassi and Trulli finally head down the pitlane and once again the sound of F1 engines fills the air.

Di Grassi gets the session underway in earnest, crossing the line at 1:48.532. Next time around the Brazilian posts a 47.992 as Trulli posts 48.549. Having had a chat with Button, Martin Whitmarsh is now in conversation with Hamilton and his engineers.

A 47.025 sees Glock go straight to the top of the timesheets as Heidfeld and Buemi begin their first flying laps. Heidfeld posts 44.415 but this is immediately beaten by Alguersuari (44.339).

As Alguersuari raises the benchmark with a 44.043, Rosberg and Schumacher head down the pitlane. With twenty-five minutes gone only seven drivers have posted times.

On his first flying lap Kubica shoots straight to the top of the timesheets, the Renault driver posting 43.186. Elsewhere, both Ferraris are now on track, as is Vettel.

Kubica consolidates his top spot with a 42.615 only to be demoted when Schumacher posts a 42.518 having gone quickest in the final two sectors.

Alonso goes third with a 42.619 while Massa takes eighth place. Button begins his first flying lap.

At half-time, it's: Schumacher, Kubica, Alonso, Hulkenberg, Vettel, Petrov, Heidfeld, Buemi, Massa and Alguersuari.

Having gone quickest in S1, Alonso backs off as Petrov goes second overall with a 42.580. Elsewhere, Rosberg runs wide. He isn't the first to do so this weekend and he won't be the last.

Vettel goes quickest in S1 as Webber finally heads down the pitlane. Alonso posts 42.291 to go quickest but moments later Vettel raises the ante with a 41.721.

Rosberg posts 42.099 to go second having gone quickest in S2. However, Vettel responds with a 41.628.

As Hamilton finally leaves the pits, Button goes sixth (42.546) and Webber eleventh (43.202).

A 42.353 sees Webber improve to fourth as Hamilton locks up big time. Nonetheless, on his first flying lap the Englishman goes second with a 41.994.

With 22:00 on the clock we've yet to see the super-softs make an appearance. Though that will change in the next ten minutes as the teams start to focus on qualifying as opposed to the opening stagers of the race.

Ferrari president Luca di Montezemolo is doing the rounds, shaking hands with Christian Horner then Michael Schumacher.