Ahead of today's opening session, the air temperature is 17 degrees C, while the track temperature is 21 degrees. It is wet, it is very wet... for when it rains at Monza it really rains... and much more is expected over the course of the day.
With further rain expected tomorrow but sunshine on race day, this presents the teams with a conundrum.
As at Spa, there is only one reserve driver on duty in this session, and that's Lando Norris who is driving Stoffel Vandoorne's McLaren.
According to the pundits, this is Ferrari's race to lose, but other than the fact that one should never write-off Mercedes and that the Maranello outfit has a tendency to shoot itself in the foot, as we all know the weather is a great leveller... as those familiar with Vettel's win here in 2008 well know.
In the moments before the session gets underway the rain stops. But the heavy, dark clouds that surround the circuit mean that few in the stands are willing to put away their raincoats just yet.
Several minutes before the green light, Ricciardo is waiting at the end of the pitlane, along with Hulkenberg. Taking on a new engine this weekend, Ricciardo will take a grid penalty.
For reasons best known to themselves, Renault play some Madonna over the radio to Hulkenberg, though the German isn't aware if it is the American singer or Kylie.
As the lights go green it begins to rain again, as Norris also heads out all three are understandably on full wets.
"I've got a problem, got a problem," reports Ricciardo as he slows through the Lesmos. The Australian is using the latest C-spec engine, which Renault has warned has more power but also has reliability issues.
"I've got no power," confirms Ricciardo. "I'm just staying in first," he reveals as he makes his way back to the pits.
As more drivers head out, Raikkonen is the first to try Inters. It's a brave gamble and a scary ride for the Finn.
Ten minutes in and all but Verstappen, Leclerc, the Panthers and Silvers Arrows have been out.
Apart from anything else, bearing in mind that we are expecting further rain this afternoon and tomorrow, the teams are limited in the number of wets and Inters available.
Verstappen heads out on the Inters.
Asked how the track is, Gasly responds: "Wet!"
Hulkenberg heads out again, and appears to be going for a time. He is still on the full wets. The German reports that he feels he should be on Inters.
At the line Hulkenberg posts 1:38.567.
After a brief lull, the rain eases and as a result a number of drivers head out, some on Inters, others on wets.
"There's no mechanical issue, the engine just went into a safe mode," confirms Christian Horner of Ricciardo's issue.
Sainz is told not to damage his (wet) tyres as they "could be really useful in FP3".
Vettel misses the second chicane while Hulkenberg has a worrying wobble in the Parabolica.
As Vettel (wets) posts 37.867 to go quickest, Sainz goes second and Raikkonen posts 38.878.
Sainz improves to 37.424 on the Inters, as Verstappen has a spin in the Parabolica. "All good, just a little drift," he reports.
Sainz raises the bar with a 36.995, as Hulkenberg makes it a Renault 1-2 with a 37.482.
Thirty-six minutes in and there are twelve names on the board.
Ricciardo goes wide at the second Lesmo, as his teammate posts 37.716 to go third.
Bottas splits the Renaults with a 37.342 as the rain appears to ease a little.
A 36.866 sees Hamilton go straight to the top of the timesheets, the Briton the last driver to post a time.
Conditions remain difficult with drivers running wide and making mistakes at just about every corner.
Activity in the Ferrari garage as the floor is changed on Vettel's car.
"I think there's a problem with engine braking," reports Grosjean, as Hamilton improves to 36.546. "Something is pushing the car."
Bottas leapfrogs his teammate with a 36.238.
"I have no grip," claims Gasly.
As the crew work on his car, Vettel is caught running through the paddock, however, he is caught by a few fans and has to stop for the obligatory selfie.
With fifty minutes remaining, the rain has stopped and it seems a little brighter.
Leclerc moves to third with a 36.648, ahead of Perez, Ocon, Sainz, Hulkenberg, Gasly and Verstappen.
Magnussen improves to seventh with a 37.066.
With the rain having stopped and the beginning of a dry line just starting to appear, it is only a matter of time before someone makes the switch to slicks.
As drivers complain of their rears overheating, they seek out the wet patches in a bid to cool them.
Ferrari reports that the spare gearbox - i.e. that currently in the car - is being replaced on Vettel's car.
Told to "box", Verstappen, who has just gone quickest with a 35.655, replies: "No, one more lap." Naughty boy.
Alonso cuts a forlorn figure as he walks through the paddock... however, as the camera closes in it's a look-a-like. Get another and they could contest F1, WEC and IndyCar next year... problem solved.
Raikkonen improves to sixth with a 36.877. However, the Finn is demoted when Sainz posts 36.262 having gone quickest of all in S2.
A significant improvement from Hulkenberg (36.107) sees the German go second, 0.442s off Verstappen's pace.
Hulkenberg fits a set of softs, but is is merely a practice pit stop and the car is pushed back into its garage.
Another improvement from Sainz (35.955) sees the Spaniard go second and demote his teammate to third.
Alonso improves to 14th with a 37.426.
A 35.873 sees Gasly go second, evoking memories of that weekend back in 2008.
As Hartley improves to sixth (36.640), Renault reports: "That's our session done", the French outfit clearly feeling that there will be no significant slick running.
Ricciardo improves to third with a 35.899, as Hartley looks set to make a significant improvement. Indeed, the Kiwi crosses the line at 35.024 to take the top spot. It's a Toro Rosso 1-2.
Ricciardo goes second with a 35.024 as Toro Rosso and Red Bulls comprise the first four.
Raikkonen heads out for a late assault. Though he has a poor opening sector, he's quickest in the two final sectors, eventually crossing the line at 35.640 to go fourth.
With four minutes remaining, Bottas appears to be heading out again.
A 34.742 sees Raikkonen go quickest, the Finn not bothering with a cool down lap.
Moments later, Ocon goes second with a 34.868, with teammate Perez posting 35.079 to go fourth.
On his third successive lap, Raikkonen raises the bar with a 34.550.
Bottas is out of his car, having abandoned the idea of a final run.
As the chequered flag is waved, Ocon posts a PB in S2, while Perez goes quickest. The Frenchman crosses the line at 34.593 while the Mexican posts 34.000 to steal Raikkonen's thunder.
Perez is quickest, ahead of Raikkonen, Ocon, Hartley, Ricciardo, Gasly, Verstappen, Sainz, Hulkenberg and Bottas.
Hamilton is eleventh, ahead of Leclerc, Magnussen, Alonso, Grosjean, Ericsson, Vettel, Sirotkin, Stroll and Norris.
Check out our Friday gallery from Monza, here.
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