For a second consecutive day, stiff runway crosswinds at NASA's coastal Florida spaceport Monday prompted mission managers to forego a pair of landing opportunities. Low-level clouds and rain also swept into the area.

The situation was just as bad or worse at a back-up site in California, preventing NASA from sending Atlantis and its crew on a cross-country detour to Edwards Air Force Base.

"Bottom line is we're waving off," astronaut Scott Altman told the crew from NASA's Mission Control Center at Johnson Space Center in Houston, Texas.

Strict NASA flight rules call for a landing attempt to be called off if runway crosswinds top 15 knots -- conditions that could make it difficult to bring a shuttle in for a safe touchdown. The winds at KSC Monday were in excess of that limit throughout the afternoon.

Cloud ceilings also must be above 8,000 feet (2,425 meters) to make certain a shuttle commander has a clear view of the runway on final approach. Low-level clouds, however, were rolling into the KSC area and also would have obscured the runway at NASA's Mojave Desert landing site.

In addition, scattered rain showers were spotted within 30 miles (48 kilometers) of both KSC and Edwards, presenting yet another flight rule violation.

Launched 12 days ago on a mission to deliver the U.S. Destiny science laboratory to the International Space Station, the Atlantis crew has enough fuel and supplies to remain in orbit until Wednesday.

Mission managers say the crew might be able to stretch those reserves until Thursday.

The Central Florida weather forecast, however, calls for generally favorable conditions at KSC's Shuttle Landing Facility Tuesday. Peak winds are not expected to top 14 knots.

The Atlantis crew will have two opportunities to land at KSC Tuesday. The second will come at 2:02 p.m. EST (19:02 GMT).

The astronauts also will have two chances to land at Edwards, where the only concern will be a chance of low-level clouds. Those will come at 3:33 p.m. EST (20:33 GMT) and 5:09 p.m. EST (22:09 GMT), respectively.

What's more, a second alternate site at White Sands Space Harbor in New Mexico will be available Tuesday if need be, and weather there is expected to be good.

But a landing there would be a rarity: In the 20-year-history of NASA's shuttle program, only one mission -- STS-3 in March 1982 -- was capped with a landing at White Sands.

Cockrell and his crewmates, meanwhile, are taking their delayed homecoming in stride, making light of the situation in conversations with ground controllers.

"The crew wanted me to tell you that I've already got the endurance record, so we don't need to try for that," Cockrell told Altman at one point Monday.

The veteran astronaut commanded NASA's longest shuttle mission to date, a 1996 space science mission that lasted 17 days, 15 hours, 54 minutes and 28 seconds.

Atlantis mission specialist Tom Jones also was on that flight.