NASA managers have options, but none of them is ideal as they consider where to land the space shuttle Friday.
The forecast calls for low clouds and showers at Kennedy Space Center, the primary site. Crosswinds are expected at the main back-up site at Edwards Air Force Base in California. The weather looks good at a seldom-used back up site in New Mexico, but that creates logistical headaches.
Thursday, on their last full day in space, Discovery's seven astronauts plan to test the flight control system, deploy a tiny satellite and give their last media interview from space.
Engineers also are expected to give a green light for Discovery to come home after studying images of its heat shield.
Saturday is the last possible day to land because the fuel that generates electricity on the spacecraft will run out.