The phenomenon I am choosing is the formation of a tornado. Agents and environment would included the temperature aloft, the temperature at ground level, humidity levels, instability in the atmosphere, and ground level and upper level wind speed and direction (among other factors). The difference between temperatures could lead to the creation of convection, the amount of moisture can cause the creation of cumulus clouds, instability can also increase the chances of rotation, etc. All of these factors interact together to increase the chances of the formation of a tornado. I think (I could be wrong) that predictions that lead to tornado watches and warning are based on this type of modeling.