3.2 Cloud Formations & Characteristics

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The FAA categorizes clouds by altitude (Low, Mid, and High level clouds) and 4 main cloud types which are cumulus, Cirrus, Stratus, and Nimbus. Within these four types of clouds are various cloud formations that possess unique characteristics throughout the different formations.

Lenticular Clouds – a lens-shaped cloud that typically develops on a down slope side of a mountain range. These clouds are developed when stable, moist air flows over a mountain, generating a series of oscillating waves.


The Cumulus Stage (3-5 mile height)

Most cumulus clouds do not grow into thunderstorms, but every thunderstorm begins as a cumulus.

The key feature is an updraft that extends from very near the surface to the cloud top.

During this stage water droplets are quite small but grow to raindrop size as the cloud grows.

The air carries liquid water above freezing level creating an icing hazard.  As rain drops grow heavier, they fall and the cold rain drags air with it creating a cold downward draft coexisting with the updraft. (6500 ft and below)

 The Mature Stage (5-10 mile height)

Precipitation beginning to fall is your signal that a downdraft has developed and entered the mature stage

Cold rain in the downdraft causes it to remain cooler than surrounding air.  Therefore, downward speed is accelerated and the rushing air spreads outward at the surface, producing strong, gusty surface winds, sharp temperature drops, and rapid pressure rises.

Updrafts & downdrafts create a very turbulent


The Dissipating Stage (5-7 mile height)

Downdrafts characterize this stage and is where the storm dies rapidly.

When rain has ended and downdrafts have abated, the dissipating stage is complete.

When all cells of a thunderstorm have completed this stage, only harmless cloud remnants remain.

Four Methods in which air reaches the saturation point

  • When warm air moves over a cold surface, the air temperature drops and reaches the saturation point.
  • The saturation point may be reached when cold air and warm air mix.
  • When air cools at night through contact with the cooler ground, air reaches its saturation point.
  • The fourth method occurs when air is lifted or is forced upward in the atmosphere.
Cumuliform clouds Stratiform clouds and fog
Showery Precipitation Continuous Precipitation
Rough air (turbulence) Smooth air
Good Visibility (except in blowing obstructions) Fair to poor visibility in hazard and smoke

FOG – Surface-based cloud that consists of either water droplets or ice particles and may form by cooling the air to its dew point or by the addition of moisture to the air near the ground.

4 types of fog on test

Advection fog (Sea Fog and or Steam Fog- light to moderate wind and requires a body of water) Warm air masses moving over a body of water cooling down to its dew-point causing fog to form. (Sea Fog)

or visa versa, cold air masses moving over warm water causing evaporation and an increase in near surface moisture. (Steam Fog)

Radiation Fog (Ground Fog- requires little to no wind and typically occurs at night and early mornings) Radiational cooling at the surface that lowers the temperature of the surrounding air resulting in saturation.

Upslope Fog (Terrain Induced Fog- Requires wind flow strong enough to forcefully move airmasses “upslope”) Moist airmass forced upslope resulting in saturation.

Precipitation Fog (Rain / Post-Frontal Fog) Precipitation falling through the air resulting in evaporative cooling leading to saturation.