Spaniard Jon Izaguirre set the pace in the second individual time trial at the 100th Tour de France as threatening clouds began to gather over the course before the leaders set off.
Chris Froome was the favourite to take victory on today's stage, a much more mountainous one than last week's to Mont-Saint-Michel in which he finished 12 seconds behind Tony Martin, but the weather may have a significant say in the outcome with the forecast pointing to rain and possible thunderstorms shortly before he and the other general classification contenders are due to set off.
The early runners were free of such concerns, with Euskaltel Euskadi's Izaguirre taking over the lead from original pacesetter Lieuwe Westra with a time of 53 minutes 58 seconds over the 32 kilometre route, just four seconds faster than Westra.
Martin, the world time trial champion, finished 41 seconds off Izaguirre's time, with a course featuring two categorised climbs not to his liking.
Earlier, Mark Cavendish finished a little over five minutes off the pace after recovering from the upset stomach which caused him some discomfort and a little embarrassment yesterday.
Geraint Thomas was three minutes off the pace and Ian Stannard 4m 39s back, with Froome's team-mates saving themselves for the challenges ahead in defending the yellow jersey.
With rain falling steadily on the climbs from around an hour before Froome was due to depart, making the descents considerably more difficult, Izaguirre's time stood unchallenged.
Team Sky said they had been prepared for the weather and Froome would take a no-risk strategy into his time trial.
"It was in the forecast and now it is a certainty," said sporting director Nicolas Portal. "We had considered the case, we include special tyres. But it is certain that this will make the descent a little more complicated.
"We know that the best will rise at a rapid pace, so he will not have to get distracted then. We'll take zero risks. It would be a shame to try to win but end up losing much more because of an error... we have a comfortable margin."
Tejay Van Garderen, last year's best young rider who has endured a difficult Tour to date, then defied the conditions to wrest the lead from Izaguirre, setting a time 34 seconds faster than the Spaniard.
"Things haven't really gone my way from the start of this Tour but I wanted to take something away and have something to be proud of and hopefully today is the day," the American said.