Dark clouds are hanging above the Monaco street circuit on Saturday morning.
Some weather reports are predicting the possibility of showers, while others believe that any rain will hold off until after the practice and qualifying sessions.
The uncertainty is a major worry for the F1 teams, because the ’parc ferme’ rules means that prior to qualifying, car setup is essentially locked in for the rest of the weekend.
"You have got to have a bit of a crystal ball," agreed Red Bull’s Christian Horner, "because the only variable you’ve got for the race is your front wing.
"I’m sure that basically the weather conditions on Saturday will principally dictate what setups people are going to end up on Sunday with," he added.