Ahead of today's qualifying session for the Grand Prix du Canada, the air temperature is 22 degrees C while the track temperature is 25 degrees. It is overcast with talk of rain after the end of the session while it is claimed that there is a more than 50 percent chance of rain tomorrow.

Mixed fortunes for Red Bull this morning with Sebastian Vettel topping the timesheets and Mark Webber sidelined with a KERS problem. Once again the Ferraris were on the pace, as were the McLaren and Mercedes, with the Force Indias giving the Renaults a run for their money.

Tyre choice this week is between soft (prime) and supersoft (option) with some sources claiming that we could be looking at 4 - 5 stops over the course of the race. Interestingly, this morning the options were good for 4 or 5 laps.

It is widely thought that the nature of the Circuit Gilles Villeneuve means that it is track where Red Bull will be least competitive this season - though someone clearly forgot to tell Vettel this morning. The same people claim that this is McLaren's best chance to bite into the Austrian outfit's championship lead however, Ferrari, and possibly Mercedes, might have their own ideas.

It's been a difficult weekend for Sauber, Sergio Perez admitting after yesterday's opening session that he felt unwell and being replaced - at ten minute's notice - by Pedro de la Rosa. Kamui Kobayashi crashed out of yesterday's second session while de la Rosa went into the barriers at the very end of this morning's session.

The lights go green and d'Ambrosio - who is driving the spare Virgin chassis after crashing yesterday - is first out. He is followed by teammate Glock and Petrov.

D'Ambrosio posts 25.366 to get Q1 underway, surprisingly, neither Glock or Petrov go quicker. Heidfeld does however, the German crossing the line at 17.120. All using the harder soft rubber - if that makes sense.

Next time around Petrov improves with a 16.083 as all 24 cars are on track - clearly some drivers don't trust the weather forecast and want to get in a 'banker' lap.

As Heidfeld goes quickest in the first two sectors, di Resta goes quickest overall (15.879), but this is quickly beaten by Webber, Heidfeld and then Alonso (14.994).

Vettel goes quickest in the first two sectors, finally crossing the line at 14.703. Elsewhere, Hamilton goes quickest in S1. The Englishman goes fourth with a 15.069 as Vettel raises the bar with a 14.318.

As Vettel goes quickest in S1, Button complains that he's struggling to slow his car down. Alonso goes quickest (14.227) but is quickly leapfrogged when Vettel crosses the line at 14.011. Alguersuari gets very, very close to the wall.

Schumacher goes sixth (14.970) but is immediately demoted by his Mercedes teammate who posts a 14.920.

De la Rosa is the first driver to switch to the option rubber, the Spaniard clouting the wall but able to continue. Elsewhere, Hamilton goes quickest in S1 as Alonso improves with a 13.822. Hamilton, improves to third overall courtesy of a 14.114 only to be leapfrogged moments later by Massa (14.026).

In the danger zone, the usual suspects are joined by Alguersuari, with Kobayashi, Maldonado and de la Rosa hovering.

The top eight wait in their garages as the fight to make it through to Q2 continues. Currently, Karthikeyan and d'Ambrosio are outside the required 107%.

Di Resta posts 14.874 thereby improving to seventh as Kobayashi slips into the danger zone. Alguersuari improves to seventeenth.

Karthikeyan posts an 18.736 which is enough to get him into the race tomorrow - though d'Ambrosio remain outside the time.

A huge effort from Kobayashi sees the Sauber driver improve to fourteenth (15.694), thereby dropping Alguersuari into the danger zone.

At the end of Q1, its: Alonso, Vettel, Massa, Hamilton, Button, Webber, Petrov, di Resta, Rosberg and Sutil.

We lose Alguersuari, Trulli, Kovalainen, Liuzzi, Glock, Karthikeyan and d'Ambrosio.

Q2 gets underway and Maldonado leads the way, followed, shortly after, by Petrov, Barrichello, Sutil, di Resta, de la Rosa and Schumacher.