Weather balloons are released twice daily 0z/12z (Zulu, Coordinated Universal Time C or Greenwich Mean Time) for coordination across the globe. A radiosonde is a small expendable instrument package attached to the weather balloon to make observations of the atmosphere. Measurements of pressure, temperature and humidity data are collected. Wind speed and direction are calculated by tracking the position of the instrument package with GPS.
Source: National Weather Service
The upper air program here at the national weather service is a critical part of our everyday operations. It is the only way we have to actually sample the atmosphere all the way up to about a hundred thousand feet. Here at the upper air building is where we actually go through the process of filling up the weather balloon. We use helium here this office. Other offices use also hydrogen. Here on a standard day we’ll put about twelve hundred grams of helium in. We launch of rain or shine, hurricanes, blizzards, pouring down rain, anything except for lightning. If we hear any thunder within fifteen minutes we cannot launch the balloon. To prepair the radiosonde we take it out of the box to take a look at it make sure all the sensors are working properly we have a highgristor that measures humidity, a temperature boom that measures temperature. Since all of this is GPS-based which you’ll see up in the dome right there, we have to make sure that the radiosonde at the office is picking up the correct number of satellites so we let it sit there for a few minutes to make sure it's catching all the correct satellites make sure all the temperature data is correct. Once that is ready to go, we can bring the radiosonde down here and launch the balloon. We attach a parachute so when the radiosonde does fall to the ground it won’t hit anybody, hit anything, cause any damage. After that we will attach the parachute and the balloon to the radiosonde. After that we launch the balloon. It gets to about a hundred thousand feet and takes ninety minutes to pop and then we quality control monitor the data for the next ninety minutes. These observations after we take them are carefully quality controlled by our staff and all of the observations go into our models to help us forecast. We also used the raw sounding data to actually help us with the severe weather/rain snow lines when it comes to winter weather and also helping us out with various other temperature and dew point predictions.