AUSTIN, Texas (Reuters) - The start of second practice at the U.S. Grand Prix was delayed indefinitely on Friday as rain lashed down amid thunder and lightning.
With marshals unable to work due to the proximity of lightning and the track undriveable in any case, big screens around the circuit advised fans to seek shelter in their cars or indoors.
The forecast for Saturday, when qualifying for Sunday's potentially title-deciding race is scheduled, was no better with heavy rainfall likely in the Austin area.
"If it's like this we can't run today. I hope tomorrow's better but the forecast doesn't look any good," said Ferrari's Sebastian Vettel. "It's a shame for the people in the grandstands."
Friday's first session was also rain-affected, although drivers did get on track with Germany's Nico Rosberg fastest for Mercedes.
His team mate Lewis Hamilton is hoping to clinch his third championship on Sunday with three races to spare. The Briton needs to beat Vettel by nine points and Rosberg by two.
Reporting by Alan Baldwin, editing by Mark Meadows