Speaking of Sondes....Here's a link to current radiosonde weather balloon ops worldwide. They are at-altitude at 0000Z and 1200Z daily. They actually launch about 45-60 minutes before that. Major airports are the usual launch sites.
The ones out west here are RS41's that operate at 404 MHz, around 60 mw and I can receive the basic telemetry from a LONG distance away. Click on your local balloon and it shows all the data including its GPS coord's, current altitude, temp etc.
Plot shows the track and predicted future track. They usually get up to around 100,000' AMSL, often higher before they burst. Then a long ride down on a parachute. (fun fact: from 105,000' the parachute has NO initial effect on the fall rate...very little air up there... LOL)
Tim
N6CC