Weather forecast: showers towards the end of Saturday but dry qualifying. Sunday rain all day. Therefore probably the only significant part of Friday's bakingly hot afternoon's practice running, with regard to the outcome of the world championship, was the low fuel running on the option tyres.
Any patterns seen in the subsequent long runs are likely to be irrelevant.
But one very clear beacon throughout the various running is that Ferrari is fast, clearly much more at home on this old-fashioned track with plenty of bumps where driveability is extra important.
Fernando Alonso was only fourth fastest in the low fuel part, 0.3s slower than title rival Sebastian Vettel, 0.5s off Lewis Hamilton's McLaren. But that Alonso time came near the end of a much longer run than anyone else. Fuelled as he was for at least seven laps, that would translate to a time somewhere on a par with Vettel's if indeed his rivals were fuelled only for the two or three laps they did.
On the long runs Felipe Massa was fastest of all. Unusually, Alonso did the long runs on the hard - and was still comparably fast. Both appeared to be able to set their times more consistently than the Red Bulls and McLarens.
Hamilton was very quick on Friday © LAT
The hard tyre is unlikely to be needed by the top teams. With the hottest track temperature seen all year - peaking at 51 degrees Celsius - it was hopelessly out of its low working range, meaning that on many cars it overheated into gripless oblivion quite early into the runs.
In the unlikely event the race were to be dry, the medium would be the preferred tyre, with a two-stop race and a very short final stint on the hard. For most of the top teams, the only time the hards will be used will be in Q1. It will be mediums for Q2 and Q3, full wets or inters for Sunday.
There's therefore no form to go on from the practices, except that the world's top three F1 drivers, Alonso, Hamilton and Vettel (in alphabetical order) look totally at home with the acrobatics the place demands.
It could be that Red Bull is running a little heavier than Ferrari or McLaren and therefore disguising its usual qualifying margin - but on race day, the quality of the drivers' performances will likely be the most significant factor.
Bereft of practice wet weather running, if we look at the wet races this year and compare the form of Vettel and Alonso it paints quite an illuminating picture. In the dry Vettel has scored 248 points this year; Alonso 192. But in the wet Alonso has scored 68; Vettel just 25.
Those numbers are skewed by the fact that the wet races took place before the Red Bull's big performance step in the last quarter of the season. But they nonetheless say something: the Ferrari works well in the wet. Add to that it appears to work well at Interlagos and Vettel's job is by no means as straightforward as that 13-point lead may make it appear.
Friday's form suggests the Ferrari is quick © XPB
In fact, Vettel has two hopes here: that he can set his habitual pole and disappear off into the distance, the only man able to see properly where he's going, with all the spray behind him.
Or that the race is so wet it gets called before three-quarter distance - in which case half points would be awarded and even if Alonso wins and Vettel non-scores, Vettel still takes the title.
All very much still to play for both contenders. It's likely to be dramatic, whichever way it unfolds.