4. Forecast Applications

Convection » Air Mass Thunderstorms Introduction

Conceptual animation of the life cycle of a convective storm

Air mass thunderstorms refer to cumulonimbus clouds that develop from ordinary convection; that is, convection due to warming of the boundary layer. The air mass thunderstorm has three stages: the cumulus stage, the mature stage, and the dissipating stage.

  • Cumulus stage: Updrafts prevail and one or more towering cumulus will form. Air is lifted to its level of free convection level of free convection and continues to rise. Precipitation may form in the upper portion of the cloud but is unlikely in the sub-cloud layer.
  • Mature stage: The mature stage is characterized by updrafts and downdrafts and rainfall. Air parcels reach the equilibrium levelequilibrium level. Updrafts may extend through the depth of the troposphere. An anvil begins to form at the upper levels, and precipitation occurs below the cloud. Evaporative cooling at low-levels forms a cold pool and a gust front that spreads out from the cloud and leads to uplift of warm, moist, unstable air, creating new cumulus clouds.
  • Dissipating stage: This stage is characterized by downdrafts. Convective rainfall diminishes while stratiform rainfall may continue from the anvil. The gust front advances away from the storm and inhibits air from being lifted into the storm.