Ahead of today's practice session the air temperature is 30 degrees C, while the track temperature is 44 degrees. Yesterday was hot, and it is expected to get hotter.
While - surprise, surprise - Mercedes set the pace in both of yesterday's sessions - Bottas in FP1 and Hamilton in FP2 - on the race sims Verstappen was looking very, very good.
Despite the heat, and given last weekend's troubles, Mercedes looked surprisingly good, especially on single lap pace.
However, as so perfectly demonstrated seven days ago, there are no points on Saturday only on race day.
On a day in which most drivers struggled, the big surprise was Grosjean who was a very impressive fifth. Teammate Magnussen didn't get to do a low fuel run so we do not know whether this was a fluke or a step forward for Haas.
That said, with the Ferrari power unit in the back and no car upgrades one struggles to think where the American team might be gaining, particularly in light of its form thus far this season.
In all honesty, even Grosjean was at a loss to explain the improvement.
Also looking good was Ricciardo, who followed up on his impressive qualifying performance at Silverstone with fourth in yesterday's second session.
Back in the Racing Point following his fortnight in quarantine, Perez showed no signs of after effects as he posted the eighth best time of the day.
The lights go green and following a brief wait Grosjean gets proceedings underway. He is followed by Sainz and Magnussen. The McLaren driver on hards and the Haas pair on mediums.
Having completed an install lap all three head back to the pits as Norris heads out.
Fact is, the temperatures are going to increase dramatically in time for qualifying - and tomorrow's race - so there is little that can be learned at this exact moment in time.
On the mediums, Norris posts the first time of the day (19.620).
As Norris continues, the Alfa pair head out, seemingly no Haas-style resurgence for them this weekend.
Raikkonen posts 19.521 and Giovinazzi 20.302 as Sainz heads out.
Russell, Ocon, Kvyat and the Ferrari pair head out as we finally get some action. A fair mixture of all three compounds.
Sainz, who complained of cooling issues yesterday, goes quickest with a 19.446, ahead of Raikkonen, Norris, Ocon, Vettel and Russell.
No sooner has Kvyat gone top with a 19.414 than Leclerc stops the clock at 18.950.
Twenty-three minutes in and the Black Arrows head out, Gasly and the Bulls the only 'no shows'.
Bottas (softs) posts 17.971, with Hamilton posting 18.324 moments later after having to back off due to traffic in the final sector.
As Gasly heads out, the Bulls wait, almost obstinately in their respective garages.
At which point Verstappen heads out, the Dutchman's car sporting a new set of softs.
As Verstappen begins his flying lap, teammate Albon heads out... on mediums.
"Tyres completely gone," says Kvyat of his 6-lap old softs.
Gasly goes fourth with a 19.097 on the softs.
An 18.487 sees Verstappen go third, 0.516s off Bottas' pace. Albon subsequently posts 19.182 to go sixth.
Hamilton goes quickest in S1 before backing off in the second sector. Nonetheless he crosses the line at 18.077.
Hamilton is told he needs to find time at the entry to Turns 4 and 7.
After 35 minutes, the highest placed medium runner is fourth placed Leclerc who is 0.979s off the pace.
PBs in the first two sectors for Verstappen, the Dutchman eventually crossing the line at 18.160 having gone purple in S3. He goes from being 0.516s off the pace to just 0.189s.
Albon also improves but remains sixth (19.110)
Currently 14th, Norris goes quickest in the first sector, despite a major wobble in the final chicane, finally stopping the clock at 18.858 to go fourth.
Sainz goes second with an 18.046 as the qualifying sims get underway.
Vettel improves to fifth with an 18.707, while Leclerc posts 18.193. The Monegasque is only one place ahead of his teammate but around 0.5s quicker.
"He complains about people blocking him all the time," says Latifi of Verstappen, "but he's not any better."
Bottas consolidates his top spot with a 17.373.
All eyes on Hamilton who posts a PB in S1 as Verstappen heads out. The world champion goes purple in S2, finally crossing the line at 17.222 to go quickest by 0.151s. He could have been quicker but he lost time in the final chicane.
Bottas is told to "use the shade from the grandstand" in a bid to save his tyres.
Albon improves to 18.371 but remains sixth, while Verstappen retakes third with a 17.737.
An 18.211 sees Gasly go sixth, ahead of Albon, Ocon, Vettel and Norris.
An 18.309 sees Stroll go seventh, only to be demoted when his teammate posts 18.096 to go fifth.
It's back to reality for Grosjean, the Frenchman is currently 13th and his teammate 16th.
Verstappen reports that such is the slow pace of his cool-down laps that he's not harvesting enough energy.
Ocon's lap is wrecked by traffic, the Frenchman experiencing a particularly hairy moment when he comes upon a car that has almost stopped on the racing line.
Like Sainz yesterday, Verstappen uses the old track at Turn 13 to get around a couple of slower cars.
A nasty snap for Kvyat in the final sector, the Russian doing well to hold it together.
A late improvement for Raikkonen who goes 14th with an 18.721.
The session is red-flagged when Ocon crashes at Turn 3.
Replay shows Magnussen overtaking the Renault then slowing and moving to the centre of the track. As Ocon, seemingly distracted, closes on the rapidly slowing Haas he loses the car and hits the inside wall, damaging the front of the car.
"Ah, Magnussen braked," says Ocon over the radio. Asked what actually happened, the Frenchman replies: "I let past Magnussen because he was on a timed lap and he decelerated."
The session will not re-start.
Quickest is Hamilton, ahead of Bottas, Verstappen, Sainz, Perez, Leclerc, Gasly, Stroll, Albon and Ricciardo.
Ocon is eleventh, ahead of Vettel, Grosjean, Raikkonen, Norris, Kvyat, Magnussen, Giovinazzi, Russell and Latifi.
The Ocon/Magnussen incident is being looked at by the stewards.
Check out our Saturday gallery from Barcelona, here.
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