Ahead of today's sole practice session the air temperature is 17 degrees C, while the track temperature is 20 degrees. It is bright and sunny though somewhat cool, particularly in the shadows.
Mercedes led the way yesterday - as ever - though the massive gap to the opposition in FP1 had been somewhat reduced by the end of FP2.
Lewis Hamilton was not altogether happy with his brakes, the Briton describing the settings as "disastrous", while his team broke the curfew last night to work on his fuel system, eventually opting to change it.
Ironically, one team that particularly struggled yesterday was Haas, which other than losing various bits from its cars due to poor bonding, suffered an overall lack of pace.
The bonding issues were not helped by the fact that both drivers made use of the unforgiving kerbs which tend to rattle much more than one's fillings.
The lights go green and Vettel leads the way, followed by Gutierrez and Raikkonen.
All are on the supersofts which were degrading very quickly yesterday. The other compounds available are soft and medium.
Grosjean is another early riser and is already complaining. "I've got a bad vibration," he warns.
Ocon sets the first time of the day, the Frenchman crossing the line at 1:41.767.
Alonso is quickest in the first two sectors before diving into the pits.
The second time of the day, a far more sensible 39.567, is posted by Ricciardo who is on the mediums. Moments later, Verstappen, also on mediums, posts 39.056.
No sign of Hamilton going out anytime soon indeed, the Briton is showing actor Christophe Waltz around his car.
Wehrlein is told to concentrate on tyre warm-up.
As Hulkenberg has a particularly scruffy lap - the German complaining that his fuel flap is still open - and Sainz has a right-rear puncture, Ricciardo improves with a 39.001.
A 39.559 sees Perez go third.
As Raikkonen goes quickest in S1, Verstappen raises the bar with a 38.973.
Raikkonen, on the supersofts, posts 38.512, just 0.4s quicker than the medium shod Red Bulls.
Wehrlein's session is over before it begun, the German is embedded in the kitty litter at T19.
The session is red flagged as marshals run to rescue the stranded Manor driver. "We need to turn the car off, turn the car off please," the driver is told.
The marshals make a futile effort to push the car out of the gravel but realising it is never going to happen the crane races to the rescue.
Replay shows Wehrlein lost the back of the car after running slightly wide and on to the kerb.
Raikkonen calls on his team to check his front wing after hitting the kerb quite hard.
Meanwhile, having remained in the car for several minutes - not aiding the marshals efforts - Wehrlein finally climbs from his car. His failure to get out of the car sooner will not be appreciated by other teams as the red flag has cost everyone valuable track time.
Indeed, the session resumes after a nine minute stoppage.
Replay reveals the team getting extremely unhappy with Wehrlein. Despite being told to turn his engine off he refuses, insisting that the marshals were coming. At one point it feels as though the engineer is going to do a Kimi and tell him to "get out of the ******* car!"
The session resumes at 10:27 and as one would expect there is a mad scramble to get back to work. The resultant traffic jam leads to the inevitable driver frustration, Vettel among the most vocal.
Both Mercedes drivers are on the softs.
Rosberg runs wide at T19 as teammate Vettel goes quickest (38.178)... despite the traffic.
Bottas goes third (38.784) as Verstappen leapfrogs his Red Bull teammate with a 38.973, the Dutch youngster still on the mediums.
Rosberg (softs) goes quickest (37.784) but is immediately demoted when Ricciardo (supers) posts 37.032.
Check out our Saturday gallery from Austin, here.
A 37.483 sees Hamilton (softs) go second, as Massa goes sixth, ahead of Bottas, Verstappen, Perez and Hulkenberg.
Button goes 12th with a 40.223. Told that his car is looking good on the soft tyre he replies: "It doesn't feel like it".
Vettel improves with a 37.894, despite having completed 5 laps on his set of supersofts.
With 23:20 remaining, all but Sainz have posted a time, the Spaniard having suffered a puncture earlier. However, the newly-retained driver is on track (on supers) and about to post his first time of the day. He crosses the line at 38.710 to go eighth.
Believe it or not, Sainz has another puncture. This time it's the left-rear however. "What the ****," cries the Spaniard. Precisely Carlos, WTF.
Elsewhere, "Check fifth gear," says Vettel. "All of a sudden I had a loss of power."
As Sainz arrives back in his garage, team crew and Pirelli technicians swarm over the car. Is this an issue with the kerbs, the tyres, the car or the way Sainz is driving. Even the FIA's Jo Bauer gets in on the act.
Back on track, now on the supers, and with only two others cars on track, Verstappen posts 36.766 to go quickest by 0.266s, though his use of the track limits is questionable.
As the post-mortem continues at Toro Rosso, with ten minutes remaining the drivers begin their qualifying sims.
Raikkonen improves to third (37.284), despite running wide in T19, a corner he has consistently struggled with.
Countryman Bottas can only manage seventh (38.188), teammate Massa, also struggling with the Williams, going with (38.607) moments later.
Raikkonen appears to fall asleep, much to Ricciardo's frustration, while there's been no sign of teammate Vettel since he warned of that gearbox issue.
Button posts 38.212 to go ninth and split the Williams duo, teammate Alonso going ninth (38.452) shortly after.
In the Manor garage the crew is having a hard time removing the front-left wheel from Wehrlein's car.
All eyes on Rosberg and Hamilton on the supers. The German only manages a PB in S1 however he goes quickest in S2. However, he subsequently aborts the lap and dives into the pits where he heads down the pitlane to perform a practice start... as he heads back out he is followed by teammate Hamilton who is on a brand new set of supers.
Hamilton crosses the line one second before the chequered flag. He posts a PB in the first sector and again in the second, finally, like his teammate before, backing off in S3. "That was really poor timing guys," he tells his team. Indeed it was.
The session ends with a Red Bull 1-2, Verstappen quickest, ahead of Ricciardo, Raikkonen, Hamilton, Rosberg, Vettel, Hulkenberg, Bottas, Button and Alonso.
Perez is eleventh, ahead of Palmer, Massa, Kvyat, Sainz, Gutierrez, Grosjean, Magnussen, Ericsson, Nasr, Ocon and Wehrlein.
Check out our Saturday gallery from Austin, here.