39-03 provides useful information for implementing operational hail suppression activities, and provides information on the successful design, conduct, and evaluation of such efforts. Because the effects of seeding clouds for hail suppression on a storm's rainfall are not fully understood, a number of hail suppression concepts have been formulated Covered are beneficial competition, early rainout, trajectory lowering, promotion of coalescence, and dynamic effects. 39-03 provides the best scientific and technical knowledge currently available on hail suppression to ascribe a process through which hail suppression should be designed, organized, and conducted to optimize the likelihood of success.