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may exceed 3,000 feet per minute, so it is inadvisable to operate a small UA in an area of rapidly building cumulus clouds. Early during the cumulus stage, water droplets are quite small but grow to raindrop size as the cloud grows. The upwelling air carries the liquid water above the freezing level creating an icing hazard. As the raindrops grow still heavier, they fall. The cold rain drags air with it creating a cold downdraft coexisting with the updraft; the cell has reached the mature stage. 

## The Mature Stage 

Precipitation beginning to fall from the cloud base is your signal that a downdraft has developed and a cell has entered the mature stage. Cold rain in the downdraft retards compressional heating, and the downdraft remains cooler than surrounding air. Therefore, its downward speed is accelerated and may exceed 2,500 feet per minute. The down rushing air spreads outward at the surface as shown in figure 3-4  producing strong, gusty surface winds, a sharp temperature drop, and a rapid rise in pressure. The surface wind surge is a "plow wind" and its leading edge is the "first gust." Meanwhile, updrafts reach a maximum with speeds possibly exceeding 6,000 feet per minute. Updrafts and downdrafts in close proximity create strong vertical shear and a very turbulent environment. All thunderstorm hazards reach their greatest intensity during the mature stage. 

## The Dissipating Stage 

Downdrafts characterize the dissipating stage of the thunderstorm cell as shown in figure 3-4  and the storm dies rapidly. When rain has ended and downdrafts have abated, the dissipating stage 'is complete. When all cells of the thunderstorm have completed this stage, only harmless cloud remnants remain. 

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