Online Ground School (Private Pilot)

Lesson 12.4: Atmospheric Stability

Atmospheric Stability 

     Reference: ACS PA , PHAK Chapter 12, AC 00-6B

If the atmosphere is in a stable state vertical movement is very little or not at all. But if the atmosphere is unstable, vertical movement increases becoming turbulent.  In this lesson we will cover:

  • Relative Humidity 

  • Temperature/Dew Point

  • Fog/Clouds

  • Air Mass

Relative Humidity

Thi

Temperature/Dew Point

They

Fog/Clouds

Clouds are formed by adequate water vapor and a method for air to cool.  As air cools it reaches its saturation point.  This process is in the form of sublimation or condensation and attaches to a particle in the air such as dust, salt, or smoke in the air.

Clouds are classified by the height of the cloud base.  Cloud bases in aviation are called ceilings.  A ceiling is reported on a METAR as:

  • Broken (BKN)

  • Overcast (OVC)

Low Clouds

  • Low to Earths surface up to 6,500 feet AGL

  • Fog is classified as a Low Clouds

  • Made of water droplets and super-cooled droplets (icing)

  • VFR flight not recommended

Middle Clouds

  • 6,500 feet up to 20,000 feet AGL

  • Made of water droplets, super-cooled droplets, and ice crystals

  • May contain moderate icing

  • Can be turbulence on cross country flights

High Clouds

  • 20,000 feet AGL and higher

  • Formed in stable air

  • Made of ice crystals 

  • No threat of icing or turbulence 

Extensive Vertical Development Clouds

  • Towering Cumulus or Cumulonimbus Clouds

  • Indicate instability in atmosphere

  • Produce lightning, hail, tornadoes, gusty winds, wind shear.

  • Most dangerous to aircraft 

List of Other Cloud Classifications
Basic Cloud Types
Lenticularus
Wave Clouds
Wave Clouds
Nimbostratus
Cumulus

Air Mass

They

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