Page 13 - ICS Siebel 8.1 and Master Template.11.16.15_Neat

Thunderstorms

Thunderstorms present many hazards to flying. Three conditions necessary for the formation of
a thunderstorm are:

1. Sufficient water vapor.
2. An unstable lapse rate; and
3. An initial lifting force (upward boost)

The lifting action can be caused by heating from below, frontal lifting, or by mechanical lifting
(wind blowing air upslope on a mountain). There are three stages of a thunderstorm; the
cumulus, mature, and dissipating stages, See Figure 3-3

The cumulus stage is
characterized by
continuous updrafts, and
these updrafts create low
pressure areas.
Thunderstorms reach their
greatest intensity during
the mature stage, which is
characterized by updrafts
and downloads inside the
cloud. Precipitation inside
Figure 3-3 Stages of Thunderstorms the cloud aids in the
development of these
downdrafts, and the start of rain from the base of the cloud signals the beginning of the mature
stage. The precipitation that evaporates before it reaches the ground is called virga. Virga is
typically associated with very turbulent conditions and should be avoided. The dissipating stage
of a thunderstorm is characterized predominantly by downdrafts.

Lighting is always associated with a thunderstorm. The frequency of lighting is a good indicator
of the severity of the storm. Upon observing frequent nearby lighting, remote PICs should recover
their crew and sUAS in order to seek cover. One way to determine the distance a storm is from
your location is to count the number of seconds it takes between when you see lighting and then
hear thunder. Take the result and divide by 5 to give you the distance in statute miles (SM). If
there is frequent lighting or multiple storms, this method may not be feasible. Ideally, remote
pilots can monitor the weather by electronic means and observe incoming systems with precise
detail.

Hail is formed inside thunderstorms by the constant freezing, melting, and refreezing of water as
if is carried about by the up and downdrafts.

Thunderstorms that generally produce the most intense hazard to aircraft are called squall-line
thunderstorms. These non-frontal, narrow bands of thunderstorms often develop ahead of a cold
front. Embedded thunderstorms are those that are obscured by massive cloud layers and cannot

DRONE PART 107 CERTICIFACTION PREPARATION COURSE 13