Ahead of today's second session the air temperature is 23 degrees C, while the track temperature is 39 degrees. It remains overcast with a 40% chance of rain.
Upgrades for this weekend see Red Bull with a new Front Wing, while at Mercedes the Sidepod Winglet has been removed.
Alpine has a new Rear Wing, Rear Suspension Fairing and Front Brake Ducts, while McLaren has a new Rear Wing (Flap & Endplate) and Beam Wing and Alfa Romeo new Rear Brake Ducts.
At Aston Martin there's a new Engine Cover, Cooling Louvres and Floor, while Haas has a new Rear Wing, Cooling Louvres and Floor Edge. Alpha Tauri has new Front Wing Flaps and Williams a new Floor, Engine Cover, Mirror, Halo Fairing, Rear Suspension, Rear Brake Duct Winglets and Rear Wing Endplate. Ferrari has no updates.
As this morning's session was cut short due to an issues with the CCTV cameras, this session has been extended by thirty minutes, with that extra half-hour added to the start of the session.
Only a handful of drivers posted times earlier and even these were unrepresentative as so few laps were completed and many cars were running aero rakes and sensors.
Consequently we expect this session to be extremely busy.
The lights go green and Bottas, this morning's pace-setter, leads the queue at the end of the pitlane.
In no time at all there are 17 drivers on track, with Hulkenberg and Magnussen the last out, leaving Albon as the only 'no show'. The mediums and softs are the tyres of choice.
Albon, incidentally, is the only Williams driver with the upgrade this weekend.
Of the first wave, Leclerc goes quickest (16.564), ahead of Perez, Verstappen, Norris and Bottas.
Alonso goes quickest with a 16.353 but Bottas responds with a 16.330. The Spaniard is on softs and the Finn on mediums.
Sainz (mediums) stops the clock at 15.859, however his teammate stops the clock with a 15.523.
"These downshifts are a joke," complains Verstappen as he goes quickest with a 15.333 on the softs.
With 1:21 remaining, Albon heads out on the softs.
Piastri goes fifth with a 15.840 on mediums, ahead of Norris, Gasly, Alonso, Ocon and Bottas.
A 15.230 sees Perez go top on the softs, as Bottas improves to fifth (15.582).
On the mediums, Gasly goes quickest (15.224), as Hamilton and Russell are at the other end of the timesheets, both appearing to be focussing on testing their upgrades.
Having expressed fears that his tyres were overheating, Verstappen subsequently raises the bar with a 14.726. Sainz goes second with a 14.902.
Sporting a lumberjack themed helmet this weekend, Bottas appropriately does a little grass cutting when he goes wide at Turn 4.
Leclerc goes quickest in the first sector, and again in the final sector, to go quickest by 0.150s.
Unhappy with his car, Alonso is having work done on the rear suspension of his car.
Toto Wolff, with Mick Schumacher and (driver development director) Jerome d'Ambrosio, by his side, stares at the monitors as his drivers get on with their own programmes.
Sainz goes quickest with a 14.196 as Ferrari focusses on pace and handling.
Alonso is back on track, the Spaniard is currently 13th (16.169), just ahead of his Canadian teammate.
Leclerc retakes the top spot with a 14.094.
Hulkenberg slows with smoke billowing from the rear of his car, the German having passed the pitlane entrance and consequently having to park on the pit straight. "I lost the engine, I lost drive," he reports."
The session is red-flagged as the Haas is pushed back to the pits, resuming with 53:00 remaining.
As the lights go green a number of drivers, among them the Ferraris, Bulls and Mercedes, head out on fresh softs.
Perez appears to brush the wall at Turn 7 and subsequently slows, though there doesn't appear to be any damage. Nonetheless, he pits for a precautionary check.
A big moment for Tsunoda as he runs wide in Turn 1.
Sainz raises the bar with a 13.844, while Albon improves to tenth with a 15.003.
"Stop the car, stop the car, stop the car!" Ocon has stopped at Turn 9, bringing out the yellows - his teammate having suffered a gearbox issue in this morning's session.
The session is red-flagged again.
The session soon resumes and among the first to improve is Russell who goes eighth with a 14.759, only to be demoted when his teammate posts a 14.356 to go fifth.
Ocon's issue appears to have been water pressure related.
No sooner has Perez gone fourth than he is demoted by Bottas who crosses the line at 14.220.
The sky is darkening and it is though that there will be rain in around 15 minutes.
"It's getting quite dark at Turn 10," reports Albon.
Alonso goes quickest in S1, finally crossing the line at 14.231 to go fifth, 0.387s off Sainz' pace.
In the pitlane, Magnussen almost trips up over a poorly released de Vries.
"Rain is coming in ten minutes," de Vries is advised.
Quickest in S2, Russell goes quickest with a 13.745, however moments later Hamilton posts a 13.718.
Warned that "rain is coming", Stroll is told to stay out and continue pushing.
Alonso improves to fourth with a 14.044.
Norris, currently 13th, 0.899s off the pace, runs wide in Turn 1. Seemingly, McLaren hasn't scored a point here since 2014.
"Is the rain still coming," asks Russell. "It looks like it might be missing us now," he is told.
The right side of Stroll's car is absolutely smothered in flo-vis the fluorescent green contrasting with the car's natural British Racing hue.
Sainz and Leclerc switch to hards as they look ahead to Sunday.
Piastri becomes the first driver to encounter the infamous Wall of Champions. "I clipped the wall," he reports, "it feels ok though."
Albon is the latest to run wide in Turn 1, as Sainz misses the final chicane.
As the wind picks up, pollen fills the air. "It's super windy," confirms Bottas, "pretty gusty."
With just under ten minutes remaining, the rain arrives at the far end of the track, but even before this a number of drivers have already pitted for Inters.
"It's not raining," says Leclerc as he is told to pit and fitted with the green-banded rubber.
Suddenly the rain really intensifies, causing Piastri's heart to skip a few beats as he is still on softs.
At the hairpin, Norris, who is now the only driver still on track, gets a huge appreciate cheer from the crowd as he slithers around on his Inters.
With two minutes remaining, the Aston Martin pair head out, along with Bottas.
With further rain expected tomorrow and Sunday it is important to get in some wet running.
Zhou heads out, followed by the Ferraris and Norris, however conditions have seriously deteriorated.
"Yeh, it's extreme here, I'm aquaplaning," reports Sainz, as Bottas has a big moment at the hairpin. "Good weather for... ducks," he reports.
The session ends, Hamilton is quickest, ahead of Russell, Sainz, Alonso, Leclerc, Verstappen, Bottas, Perez, Stroll and Gasly.
Piastri is eleventh, ahead of Magnussen, Norris, Zhou, Tsunoda, de Vries, Albon, Ocon, Sargeant and Hulkenberg.
Check out our Friday gallery from Montreal here.