The temperature will decrease approximately 3.5 degrees for every 1000 ft the balloon rises.
A chronological update thus far ...
They’re clearing air space over Denver International now. The balloon is at 2K ft.
The weather is about 70 degrees in Denver today so they’re not as concerned about the temperature. There are conflicting reports about whether the balloon is made of mylar or charged foil. They are unable to communicate with the boy inside at this point.
Area news stations are tracking the balloon with helicopters but they are afraid to get to close to him because the helicopter may disrupt the air currents. The FAA is working with skydivers to develop a plan.
The balloon is travelling at 25 mph and has reached 6000 ft.
They believe the balloon has extended to its maximum height and will not go any higher. There are conflicting reports that it is at 2K or 6K feet.
Balloon is 20 ft long and 5 ft high. It contains a plywood structure at the base where the child is sitting. The balloon is about an hour and a half NE of Denver.
It is a helium balloon. Helium will leak slowly, but they don’t know how long it will take to come down on its own.
They believe the balloon is at 8K ft. The plywood base on which the boy is sitting is very thin and not designed to withstand impact. The balloon was not intended to fly.
The balloon is expected in metro area Denver within the hour. They’re beginning to worry about buildings, trees, hire wires, and freeways should the balloon begin to descend. They cannot put a helicopter over the balloon because the wind would suck the balloon up into the blades. (OMG)
They do not believe the balloon is deflating. The helium is contracting and expanding as the balloon encounters colder pockets of air. It has descended to approximately 6K ft.