$_{Figure 4-33.}$  Constant pressure analysis chart. $_{Figure 4-32.}$  Lifted index chart. decision regarding the likelihood of thermal and potential  thunderstorms, and if a safe flight can be conducted.  The KI and LI can be used together to determine the moisture  and stability characteristics of a particular air mass. The  air masses may be classified as moist and stable, moist  and unstable, dry and stable, or dry and unstable. This  determination allows the balloon pilot to make an informed  A constant pressure analysis chart or isobaric chart is a  weather map representing conditions on a surface of equal  atmospheric pressure.  [Figure 4-33]  For example, a 500 mb  chart will display conditions at the level of the atmosphere at  which the atmospheric pressure is 500 mb. The height above  sea level at which the pressure is that particular value may  vary from one location to another at any given time, and also  varies with time at any one location, so it does not represent  a surface of constant altitude/height. Constant pressure charts provide the pilot with a clearer  picture of how the atmosphere behaves at different altitudes  and pressures. For example, a low pressure system that seems  insignificant based on surface observations may prove to be  a major factor in the weather at five or ten thousand feet. Constant pressure charts are prepared for selected values of  pressure and present weather information at various altitudes.  Standard charting values are at 850 mb (approximately 5,000  feet MSL), 700 mb (approximately 10,000 feet MSL), 500  mb (approximately 18,000 feet MSL), as well as higher and  lower altitudes. Charts with higher pressure altitudes present  Constant Pressure Analysis Charts  4-33