Refer to figure.
A typical airmass thunderstorm consists of three states – initial stage (cumulus stage), Mature stage and Dissipating stage:

CUMULUS STAGE/INITIAL STAGE

• Lifting action initiates the vertical movement of air
• Because of the strong updrafts (as great as 3000 ft/min), precipitation usually does not fall. Instead, the water droplets or ice crystals rise and fall within the cloud, growing larger with each cycle.
• The cloud reaches the mature stage in about 15 minutes.

⇒ This stage is characterized by continuous updrafts.

MATURE STAGE

• As the water droplets in the cloud grow too large to be supported by the updrafts, precipitation begins to fall. This creates a downward motion in the surrounding air and signals the beginning of this stage.
• The down-rushing air spreads outward at the surface, producing a sharp drop in temperature, a rise in pressure, strong gusty surface winds and turbulent conditions.
• Within the thunderstorm cloud, the strongest turbulence occurs in the shear between the updrafts and downdrafts (below the cloud).
• As the thunderstorm advances, a rolling, turbulent, circular shaped cloud might form at the lower leading edge of the cloud => this is called a roll cloud.
• It can last up to 30 min

⇒ Thunderstorms reach their greatest intensity during the mature stage (which is signaled by the beginning of precipitation at the surface).

DISSIPATING STAGE

• As the mature stage progresses, more and more air aloft is disturbed by the falling drops. Eventually the downdrafts begin to spread out within the cell – taking the place of the weakening updrafts. During this stage the upper level winds often blow the top of the cloud downwind, creating the familiar anvil shape.

⇒ Thunderstorms reach this stage when downdrafts become the dominant air movement within this cell.