Following on from Monday's incredibly cold temperatures and drizzly rain, the conditions didn't improve much for Tuesday's running - in fact, it even snowed at one point, towards the end of the day.
The Mercedes-AMG F1 W09 EQ Power+ was back out on track for day two of 2018 Formula One pre-season running, with Valtteri the team's sole driver in the car as he rattled through the team's programme.
Initially, the plan was to split running between Valtteri and team-mate Lewis Hamilton on the second day of the test, but in order to maximise mileage it was decided to keep Valtteri in the car.
There was no lunch break at the Circuit de Barcelona-Catalunya on Tuesday, allowing teams to claw back some of the track time lost due to the chilly weather conditions.
Valtteri's day was dominated by the weather - F1 tyres aren't designed to be run in such cold conditions, which made it tricky for all teams to get the most out of the session.
Nevertheless, the Finn ploughed on and completed 94 laps, putting in a best time of 1:19.976 on the Medium tyre in the slightly warmer afternoon running - which put him second quickest.
"It was very cold on track today; I don't think I've ever driven in such cold conditions before in Formula One," he said. "Testing is always difficult in these temperatures, the tyres are just not made for these conditions.
"But we made the most out of the day. In the morning, we focused on aero work with different aero rakes on the car, running various tests. In the afternoon, I was doing long runs and we also worked on the set-up.
"It was quite tricky in these temperatures, but we managed to get some work done and found some answers to our testing items.
"The weather is obviously unfortunate, but there's nothing we can do about it and it's the same conditions for everyone. In these conditions, I would say today was a good day. I hope that the weather is going to get better soon and I'm looking forward to tomorrow and Thursday."
Lewis was originally scheduled to run on Tuesday but when it comes to pre-season testing, plans can always change.
With the tricky conditions and the time it takes to swap drivers, the decision was made for Valtteri to stay in the W09 for the afternoon too, with Lewis returning to the cockpit on Wednesday.
"With the weather conditions being up and down and the loss of track time we had yesterday, it made sense to keep Valtteri in the car this afternoon," Lewis explained.
"Having run in the morning, he was comfortable in the car already and we would have lost about an hour of running time with the driver switch.
"With no real understanding of whether good weather was coming or not, I took the decision to sacrifice that time in order for the team to gain better understanding of the car by going through the run plan."
| Pos. | Driver | Team | Laps | Time |
| 1 | Sebastian Vettel (5) | Ferrari | 98 | 1:19.673 |
| 2 | Valtteri Bottas (77) | Mercedes-AMG Petronas Motorsport | 94 | 1:19.976 |
| 3 | Stoffel Vandoorne (2) | McLaren | 37 | 1:20.325 |
| 4 | Max Verstappen (33) | Red Bull | 67 | 1:20.326 |
| 5 | Carlos Sainz (55) | Renault | 65 | 1:21.212 |
| 6 | Pierre Gasly (10) | Toro Rosso | 82 | 1:21.318 |
| 7 | Robert Kubica (40) | Williams | 48 | 1:21.495 |
| 8 | Sergey Sirotkin (35) | Williams | 52 | 1:21.822 |
| 9 | Esteban Ocon (31) | Force India | 79 | 1:21.841 |
| 10 | Charles Leclerc (16) | Sauber | 81 | 1:22.721 |
| 11 | Kevin Magnussen (20) | Haas | 36 | 1:22.727 |
