As Valtteri was the first of the team's two drivers to get behind the wheel of the W09 on Thursday, he had to contend with damp but gradually drying conditions. It was no issue for the Finn, though, and proved to be an incredibly useful session.
Valtteri's best time of 1:22.789 on the Medium tyre was shuffled down to 12th place by the chequered flag, but he completed 60 laps in total - a very healthy tally, with plenty of valuable information gathered from his on-track exploits.
"We started in the wet today and got some very useful running done on both the Wet and the Intermediate tyres," he explained.
"I did a long run of roughly 30 laps on the Intermediates and could really feel the track conditions evolve during that run. We got some insights into the Intermediate tyres and their durability in temperatures like these.
"We later had a cross-over, changing from Inters to slicks tyres with a pit stop. That was very useful for the strategy team, but also for us as the drivers, as you learn a lot when you try and find the grip on the slicks and feel how the car behaves.
"I did about 60 laps which is what we had targeted. It would have been nice to drive a little more in the dry, but I think we made the most out of these conditions. Everyone in Brackley and Brixworth has done an amazing job, everything on the car worked so well since day one and the engine is running very smoothly as well."