Felipe Massa says that predicted dry conditions for the remainder of the Monaco Grand Prix weekend led to an absence of track action when wet weather struck the second practice session on Thursday.
Heavy rain hit Monte Carlo 15 minutes into the session and drivers remained in the pit lane until the final 10 minutes, before emerging for some exploratory laps.
"It hasn’t been as productive a day as we would have liked as the rain restricted our running," said Massa, who ultimately placed 12th.
"Our focus is on Saturday and the forecast says no rain, so there was nothing for us to learn running in the wet.
"We had a good first session running on the soft tyre and will take the data we have from that. Free practice on Saturday morning will be important to get the car set-up correctly."
Team-mate Valtteri Bottas had a quiet day and says that Williams needs to focus on ensuring tyres are at their optimum temperature for the remainder of the weekend.
"We struggled to get the soft tyre working at its optimum and missed the chance to try the Super Soft due to the weather, but that is the same for everyone," he said.
"We have a lot of work to do to make sure tyre temperatures are correct but have little data to go from."