The radiosounding systems of the Servei Meteorològic de Catalunya (Meteorological Service of Catalonia) permit an understanding of atmospheric conditions through the measurements of pressure, temperature, relative humidity and the wind speed and direction from the surface to heights of more than 15 to 20 km. This information is of particular importance, especially for the diagnosis of meteorological conditions with great stratospheric instability which can cause intense precipitation (or heavy rainfall). Since April 1998, radiosoundings have been carried out twice daily (at 00 GMT and 12:00 GMT) in Barcelona, at the University of Barcelona (with the collaboration of the Department of Astronomy and Meteorology). The numerical weather prediction models need this class (or type or kind?) of information for their initialization as they work with data from the surface as well as from more than 20 atmospheric layers of altitudes up to 15,000 metres. The data from these soundings are introduced daily into the mesoscale numerical models which are operating at the SMC, and there’s a substancial improvement of their forecasts for Catalonia.