the external temperatures of our yesterday's last flight in a height of 25,000m was -7.3°C, internal temperature was +2.6°C. All datas like internal and external temperature, GPS position and height, pressure and humidy are stored every two seconds on a SD on our Datalogger STRATO3. Here you find some graphs about internal and external temperature:
And here you find the complete curve of the temperatures:
Stratoflights launchs several weather balloons each week. I can't remember that we had an internal temperature of +20°C in an altitude of 20,000m. It is for us not necessary, because our equipment works also in hard conditions reliable. Why is this temperature in this altitude important for you?
Here you find some more information about our Datalogger STRATO3:
your team of Stratoflights