The beginning of surface rain with adjacent updrafts and downdrafts initiates the mature
stage. By this time, the peak of the average cell has attained a height of 25,000 feet or
more. As the raindrops begin to fall, the frictional drag between the raindrops and the
surrounding air causes the air to begin a downward motion. The descending saturated
air soon reaches the level where it is colder than its environment. At this level, its rate of
downward motion is accelerated. This accelerated downward motion is a downdraft.
Anvil or Dissipating Stage
Throughout the life span of a mature cell, as more and more air aloft is being dragged
down by falling raindrops, the downdraft spreads out to take the place of the dissipating
updraft. As this process progresses, the entire lower portion of the cell becomes an area
of downdraft. Since this is an unbalanced situation and the descending motion in the
downdraft affects a drying process, the entire structure begins to dissipate. The high
winds aloft have now carried the upper section of the cloud into the anvil form, indicating
that the cell is starting to dissipate.
It is important that you be familiar with the following information provided on
thunderstorm weather. This knowledge will assist you in providing service to pilots that
are in or around a thunderstorm.
Precipitation in a storm may be ascending if encountered in a strong updraft. The
precipitation may be suspended, seemingly without motion yet in extremely heavy
concentrations, or it may be falling to the ground. A pilot could enter a cloud and be
swamped by rain even though none has been observed from surface positions. Rain is
found in almost every case of cloud penetration below the freezing level. Where no rain
is encountered, the storm has probably not developed into the mature stage.
Various sizes of hail are present within most thunderstorm cells. The presence of
damaging hail within the cloud and under the cloud should always be considered with
moderate or severe storms. Hail may be encountered up to 25 miles downstream
(ahead) of a thunderstorm in the clear air under the thunderstorm anvil.
Moderate to severe turbulence may be encountered up to 20 miles from the center of
severe storms at any altitude and up to 10 miles from the centers of less severe storms.
Severe or extreme turbulence is most often found in the anvil cloud 15 to 20 miles