Watch this video about weather balloons from the National Weather Service in New York.
Source: Preparing and Launching a Weather Balloon | US National Weather Service | YouTube
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 - up to about a hundred thousand feet.
Here at the upper air builing is where we actually go through the process of filling up the weather balloon. We use helium here this office other offices also use hydrogen, and here on a standard day we'll put about twelve hundred grams of helium in. We launch, rain or shine, hurricanes, blizzards, pouring down rain, anything except for a lightning. If we hear any thunder within fifteen minutes we cannot launch the balloon.
To prepare the radiosonde we take it out of the box, take a look at it, make sure all the sensors are working properly. We have a hygristor 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, to 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 attached 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 you about a hundred thousand feet, takes ninety minutes to pop. And then we quality control and monitor the data for the next ninety minutes.
These observations, after we take them, are carefully quality controlled by our staff, and then all of the observations go into our models to help us forecast. We also used the raw sounding data to actually help with severe weather, rain-snow lines when it comes to winter weather, and also helping us out with various other temperature and dew point predictions.