Five Necessary conditions for thunderstorm are as follows Instability through a reasonable depth of the atmosphere Enough humidity to sustain / feed deep convection through a reasonable depth: advection of warm, humid air at low levels greatly assists thunderstorm development Cloud tops reaching to a level where the temperature is at least - 18°C. A large amount of energy available to be released. Something to ’kick it all off'-a ‘trigger' or initiating action (differential surface heating, orographic ascent, frontal (conveyor) ascent, mass convergences, coastal or sea-breege convergence, vorticity-driven forcing).