|United States Grand Prix|
|Venue: Circuit of the Americas, Austin, Texas Dates: 23-25 October|
|Coverage: Live text and radio commentary of all three days, plus BBC TV highlights of qualifying and the race. Full details here.|
The United States Grand Prix is shrouded in uncertainty as a result of heavy thunderstorms in Texas on the periphery of Hurricane Patricia.
Second practice at the Circuit of the Americas near Austin was cancelled as a result of the storms.
With up to 30cm of rain forecasted to fall on Saturday, qualifying could be postponed until Sunday.
Ferrari's Sebastian Vettel said: "If it's like this, we can't run. It does not look good."
Lewis Hamilton's team-mate and title rival Nico Rosberg set the pace in a rain-affected first practice.
The German, needing to beat team-mate Lewis Hamilton to retain his slim title hopes, headed Red Bull's Daniil Kvyat. Hamilton was an unrepresentative fifth.
The Briton needs to beat Vettel by nine points and Rosberg by two to win the title this weekend.
Officials have not yet made specific contingency plans because the weather forecast is changing so frequently.
However, governing body the FIA is open to the possibility of changing the weekend timetable to try to ensure qualifying can take place if there is a window of dry weather.
The worst of the weather is expected to subside by Sunday, when the race is scheduled for 1400 local time (1900 GMT).
If it is not possible to run qualifying on Saturday, officials have the choice of running it on Sunday morning before the race, or deciding the grid by another method.
Hurricane Patricia, which is on its way to Mexico, is one of the strongest tropical storms on record.
The storm is even raising concerns about the forthcoming race in Mexico next weekend.
If it causes extensive damage in the capital Mexico City, there could be a knock-on effect for the race at the Autodromo Hermanos Rodriguez track, which is hosting a grand prix for the first time since 1992.
|Title permutations: Can Hamilton win in Austin?|
|If Hamilton wins, Vettel must finish second to prevent Hamilton winning the title at the US GP|
|If Hamilton finishes second, Vettel must finish fifth or Nico Rosberg must win the race to prevent Hamilton winning the title|
|If Hamilton finishes third, Vettel must finish sixth or Rosberg must finish second|
|If Hamilton finishes fourth, Vettel must finish eighth or Rosberg must finish third|
|If Hamilton finishes fifth, Vettel must finish ninth or Rosberg must finish fourth|
|If Hamilton finishes sixth, the title battle will continue to the next race in Mexico, even if Vettel does not finish or collects no points. Rosberg would need to come fifth to still be in contention.|
A modern classic
Any country considering a model for a new Formula 1 race could do far, far worse than look at what Austin, Texas, has achieved with the US Grand Prix.
For a start, there's the track. In marked contrast to many of the so-called Tilke-dromes that have proliferated in recent years, the Circuit of the Americas has real character.
Elevation change, a good selection of challenging corners of differing speeds, the real possibility of creating proper racing and decent viewing.
Beyond that, Austin itself is a superlative host city - vibrant, cosmopolitan, friendly and blessed with great nightlife.
In just three short years, the race has already become a modern classic.
It really is the standard to which all new races must aspire - but from which, sadly, so many fall short.