Clocks ticking toward shuttle launchbut clouds and showers a concern Tuesday

Shuttle Discovery, the Harmony module and seven astronauts are ready to fly Tuesday and the launch team is tracking no issues, but clouds and showers could be trouble.

"We're tracking no issues," said Charlie Blackwell-Thompson, the NASA test director.

The countdown officially began at 2 p.m., ticking toward an 11:38 a.m. liftoff Tuesday.

Thompson said the team is prepared to make up to four launch attempts in five days, beginning Tuesday, if that becomes necessary because of the weather.

The weather forecast issued this morning calls for a 40 percent chance of clouds and showers preventing a launch on either Tuesday, Wednesday or Thursday morning.

A frontal boundary moving into the area today should bring showers beginning today and lasting throughout the week, shuttle weather officer Kathy Winters said. Winters foresees the front moving out of the area by launch day, but cumulus clouds within 10 miles of the pad and lingering showers could be a problem.

Read the full weather forecast here.

"We have no concerns at this time," said Glen Chin, who is the STS-120 payload manager. Harmony is a connecting node that will allow the future addition of the European and Japanese science labs to the International Space Station.

Check back often this weekend for updates on the final preparations at Kennedy Space Center.