The National Weather Service collects upper air data twice a day at 92 sites across North America. These sites release a balloon and instrument at 1100 and 2300 Universal Time Coordinated (UTC), allowing comparison of the collected information. The instrument, called a radiosonde, measures atmospheric pressure, temperature, humidity and wind speed and direction every six seconds. This data is transmitted back to the release point where it is plotted and quality controlled. The upper air data is coded (at mandatory and significant levels) and forwarded to the National Centers for Environmental Prediction, where they are used to develop computer forecast models. The data are also plotted on a skew-t diagram for operational use.

The upper air program has progressed from early kites and free-floating balloons to laser profilers and satellites. Data is also collected worldwide and shared through the World Meteorological Organization.

The balloons carry the package to heights above 100,000 feet. After the balloons burst, a small parachute will carry the radiosonde gently back to earth. When the instrument is found, directions written on the outside instruct the finder to use an included mailing bag and return the instrument for re-use. About 40 percent of the instruments are recycled.

Find out about the radiosonde replacement program.