The United States Grand Prix has postponed qualifying until Sunday morning before the race because of torrential rain.
Rain has pounded the Circuit of the Americas for two days. Lightning already forced Friday afternoon's practice to be called off.
Drivers completed a wet, hour-long practice session Saturday morning. Championship leader Lewis Hamilton of Mercedes had the fastest lap, topping Ferrari's Sebastian Vettel.
More heavy rain moved in, forcing a three-hour delay before officials postponed qualifying until Sunday. The worst weather is forecast to move from the area overnight, although it could still be raining when the drivers return.
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Hamilton is chasing his second consecutive world championship and third overall. He can clinch the title Sunday if he outscores Vettel by nine points and Mercedes teammate Nico Rosberg by two.