Ahead of today’s opening free practice session the air temperature is 17 degrees C, while the track temperature is 18 degrees. F1 returns to Europe and guess what, it’s cold and it’s raining.

This being where the 2013 season really gets going, all the teams have loads of updates – Mercedes even has a new (more silver) livery, but if conditions don’t improve they are unlikely to get much information from them.

After four races it’s still fairly well balanced even though Sebastian Vettel has two wins to his name. However, with Ferrari, Lotus and, to an extent, Mercedes, still looking good it is hoped that Red Bull doesn’t get it all its own way otherwise attention will shift to 2014 leaving Vettel to take his fourth successive title.

This is an important race for everyone, but in particular McLaren and Williams, both multi-championship winners and both winners here in Barcelona.

Not only has Pirelli changed the compound of its hard tyres for this weekend – and onwards – the teams will have access to an extra set of prototype (unmarked) hard tyres in an effort to promote more running. Though in this weather…

The lights go green but there is no rush to get to work. That said, after a couple of minutes Bianchi and Chilton head down the pitlane.

Rodolfo Gonzalez is the on duty again this morning, the Venezuelan in Chilton’s Marussia. At Caterham, Heikki Kovalainen is in Pic’s car.

As more drivers pour – no pun intended – on to the track, some are on inters and others on full wets.

An early mistake sees Grosjean (inters) spin, the Frenchman losing the back of the Lotus in T10.

Ten minutes into the session all but Button, Perez and Rosberg have been out.

Hulkenberg is the first driver out for a second run, the Sauber star subsequently posting the first time of the day (1:51.644). Next time around, as the TV camera cuts to spare parts arriving at the McLaren garage, the German improves to 48.508.

Nineteen minutes into the session, Perez leaves the pits, the underside of his car smothered in flo-vis. After a single lap the feisty Mexican returns to his garage.

With just over an hour remaining, Massa, Hamilton and Vettel are on track. They are subsequently joined by Grosjean.

A 45.023 sees Massa go quickest, the cameras picking up a big slide from the Brazilian and an off-track excursion from Grosjean. The Frenchman subsequently posts 45.974.