This plot is a skew T-ln P diagram that is produced from every radiosonde balloon deployment. It tells us the thermodynamic profile of the atmosphere. The red line is temperature, the blue line is dewpoint temperature, which is the temperature at which water vapour starts to condense. The point where the two lines get close together is where the cloud base sits, at about 1 km high. Wind direction is shown on the right-hand side, indicating that the wind was northerly near the ground and westerly higher up. In this particular deployment we lost the signal at 7 km high, but usually the radiosondes can reach about 15-20 km.