Ahead of today's sole practice session the air temperature is 18 degrees C, while the track temperature is 22 degrees. It is raining.

Upgrades this weekend see Red Bull with a new Engine Cover (Cooling), Ferrari with a new Rear Wing and Mercedes with new Sidepods, Engine Cover, Floor and Rear Wing.

Alpine has a new Floor and Front Wing (Flaps), McLaren a new Rear Wing (Endplate & Flap) and Beam Wing, Alfa Romeo a new Front Wing (Flaps), Rear Wing and Beam Wing and Aston Martin a new Rear Wing (Flap), Beam Wing and Floor (Edge).

Finally, Alpha Tauri has a new Rear Wing (Tips), while Haas is the only team that has brought nothing new.

A significant upgrade package from Mercedes which the German team will be hoping can help it make up the ground lost to McLaren in recent weeks.

Of course, this being a Sprint weekend, there is only this session before we head into qualifying this afternoon.

The lights go green and Albon leads the way, the Williams sporting Inters. He is followed by Sargeant, who is on Inters) and Hamilton who is on full wets.

As Russell, Tsunoda and Bottas head out, all sporting full wets, the rain intensifies.

As Albon posts an exploratory 2:08.394, even on the full wets Hamilton is struggling.

"We have heavier rain in the pitlane," he is warned as he crosses the line at 2:10.299.

Elsewhere, Russell appears to aquaplane on the approach to Les Combes, while Albon misses the final chicane.

Tsunoda goes second with a 2:10.108, ahead of Hamilton, Russell, Zhou and Ricciardo.

The Japanese subsequently has a moment at Eau Rouge.

As conditions worsen, the track falls silent.

Eventually Sainz breaks the deadlock, the Spaniard heading out on full wets. He is subsequently followed by former teammate Norris. Gasly and Ocon head out on Inters.

Sainz goes second with a 9.081 as the Bulls head out, both on full wets.

"We can confirm that the teams have been informed that Free Practice will not be used to set the grid for either the Sprint or the Grand Prix this weekend," announces the FIA. "This has been done to ensure the teams do not treat the first session of the weekend as a competitive session.

"While the situation regarding the weather is constantly evolving, the priority will be to run a qualifying session for the Grand Prix. Other sessions may be cancelled or rescheduled to facilitate this, and if it is impossible to run a qualifying then the grid will be set by championship order."

Norris (Inters) goes quickest, ahead of Leclerc and Perez. Who are both on full wets.

Sainz improves with a 3.207 as Piastri goes second, the top three all on Inters.

The session is red-flagged when Sargeant goes off at the top of the hill.

"I couldn't turn," he reports, "something broke, man."

The American is one of five drivers, including Verstappen and the Alpines, yet to post a time.

The session resumes with 20 minute remaining. However, it is almost 8 minutes before Perez breaks the deadlock. He is followed by his teammate, both are on Inters.

As the Bulls pit, the Aston Martins head out.

"Rain very heavy, we're boxing this lap," Stroll is told, almost as if he hadn't noticed.

Strangely, after several more minutes of total inactivity, with 1:30 remaining, Zhou and Leclerc head out, presumably for practice starts. They are followed by Bottas, Hamilton, Sainz, Magnussen and Hulkenberg.

Some are on full wet other on Inters, consequently it is no surprise that some are far more cautious than others.

The session ends. Sainz is quickest, ahead of Piastri, Norris, Leclerc, Perez, Albon, Tsunoda, Magnussen, Ricciardo, Hulkenberg, Alonso, Hamilton, Russell, Bottas and Zhou.

Check out our Friday gallery from Spa here.