CAPE CANAVERAL, Fla. -- NASA's outlook for the final launch of the shuttle Atlantis on Friday worsened today with a 70 percent chance of bad weather.

Forecasters on Tuesday had said their would be a 60 percent chance of a no-go at launch time because of possible rain and thunderstorms near Kennedy Space Center. NASA's scheduled launch time for the resupply mission to the International Space Station is Friday at 10:26 a.m. CDT.

The forecast for a Saturday launch opportunity also worsened, from a 40 percent chance of a no-go at launch time to a 60 percent chance of unfavorable conditions.

NASA protocol requires there be no thunderstorms within 20 nautical miles of the launch site, mainly in the case of an aborted flight after the launch, which has never happened, according to the agency.

One of NASA's contingency plans would involve the shuttle dropping it's external fuel tank and rocket boosters above the Atlantic Ocean, then turning around and making an abort landing at Kennedy Space Center. That unlikely option would be unavailable with thunderstorms in the area, said Allard Beutel, a NASA spokesman.

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