If you can learn to fly a glider, it won't take you more than a few minutes to learn how to use this effectively. It does take a bit of practice, because the slightest change will produce vastly different results. So use it on a regular basis, and you will be able to confidently predict thermals. Thermals are parcels of air, which are forced to rise to higher altitudes because they are warmer than the air surrounding them. When forecasting thermals on this chart, we use adiabat guide lines to move that parcel of hot air upward.
Gravity holds the air - the atmoshpere, around the earth.
The weight of the air is called atmosheric pressure, and this pressure is measured in millibars. The dry adiabat line is a simple relationship between the pressure and the temperature of dry air. Look at the Thermal Adiabat Soaring Chart, and locate the adiabat line at SL and 86 F. Follow that line up to 3,500 feet, and you will see the temp of that same air would be 68 F if it only had 880 millibars of pressure on it. That's a fact. It's just a simple law of physics.