Theory

• Thunderstorms develop in hot humid air and are characteristed by violent and heavy precipitation associated with thunder and lightning. In urban areas, the chance of thunderstorms is increased, particularly during the late afternoon and early evening in the summer months.
• Thunderstorms are produced by convectional uplift under conditions of extreme instability. Cumulonimbus clouds may develop up to the height of the tropopause, where the inversion produces stability. The updraught of air causes rapid cooling and condensation, leading to the formation of water droplets, hail, ice and super-cooled water. During condensation, latent heat is released, fueling convectional uplift.
• As raindrops are split in the updraught, positive electrical charge builds up in the cloud. When the charge is high enough to overcome resistance in the cloud or atmosphere, a discharge occurs to areas of negative charge in the cloud or to Earth. This produces lightning. The extreme temperatures generated caused cause a rapid expansion of air which develops a shock wave. This is heard as thunder.