A cloudy weather forecast raised doubts Wednesday about whether the space shuttle Discovery would get off the launch pad this weekend for the space shuttle's first launch in nearly a year.

There was a 60 percent chance that clouds which can trigger lightning strikes would prevent a launch during the 10-minute window Saturday afternoon, said Kathy Winters, shuttle weather officer.

The weather forecast remained the same for Sunday and Monday and was expected to worsen later in the week.

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NASA test director Jeff Spaulding said the space shuttle currently had no technical problems that would prevent a launch attempt.

The space agency would make maximum of four launch attempts over five days starting Saturday, if needed. The launch window extends until July 19.

The countdown to liftoff was set to begin late Wednesday afternoon.

Saturday's launch would be just the second shuttle flight since the Columbia disaster in 2003, which killed seven astronauts, and the first since the liftoff of Discovery last July.

"Obviously these forecasts, while they sound a little bit gloomy, we've certainly launched with higher predictions of no-go," Spaulding said.

During the 12-day mission, Discovery's seven-member crew will test shuttle inspection and repair techniques, bring supplies and equipment to the international space station and deliver the European Space Agency's Thomas Reiter for a six-month stay on the orbiting space lab.

Astronauts Piers Sellers and Mike Fossum will make two spacewalks, and possibly conduct a third one which would add an extra day to the mission.

Spaulding said a fuel tank scheduled to be used on the next shuttle mission would be ready despite slight damage from a work platform last week.

During repairs, workers also discovered water from Hurricane Katrina flooding in the tank, which was constructed at a facility outside New Orleans.

The Kennedy Space Center also will be testing out new techniques for keeping birds, particularly vultures, away from the launch pad during liftoff.

A vulture struck the fuel tank of space shuttle Discovery during last year's launch, but didn't cause major damage.