Meteorology
Clouds
Lesson 4.2
Sep 2012
Reference
From the Ground Up
Chapter 6.2:
Clouds
Pages 124 - 127
Introduction
• Clouds can form in different ways and,
as a result, come in many different
types.
• Pilots should know the properties of
different types of clouds, and what
weather conditions come with them.
Outline
• Classifications
• Sky Condition
• Cloud Formation
Classifications
• By formation:
– Cumulus – Vertical clouds, formed by rising air,
indicates Unstable Air
– Stratus – Horizontal layers, indicates Stable Air
• By height (families):
–
–
–
–
Low (Strato)
Middle (Alto)
High (Cirro)
Vertical Development
Surface – 6 500 ft
6 500 ft – 23 000 ft
16 500 ft – 45 000 ft
1 500 ft and up
High Clouds
• Cirrus (Ci)
– Thin wavy, delicate wisps
High Clouds
• Cirrocumulus (Cc)
– Thin cotton ball or flake-like
High Clouds
• Cirrostratus (Cs)
– Very thin, high sheets
– Makes sky white, halo around sun or moon
Middle Clouds
• Altocumulus (Ac)
– Layer or patches of rounded masses
Middle Clouds
• Altocumulus Castellanus (Acc)
– Altocumulus with turrets
Middle Clouds
• Altostratus (As)
– Thick grey layer
– Sometimes light rain/snow
Low Clouds
• Stratus (St)
– Uniform layer like fog, but not on ground,Sometimes has
drizzle
– When broken, called Stratus Fractus (Sf)
Low Clouds
• Statocumulus (Sc)
– Thin layer or patches of rounded masses
Low Clouds
• Nimbostratos (Ns)
– Uniform thick, dark, grey layer
– Continuous rain/snow
Vertical Development
• Cumulus (Cu)
– Thick, rounded or lumpy individual clouds
– When fragmented, called Cumulus Fractus (Cf)
Vertical Development
• Towering Cumulus (TCu)
– Very high towering masses
– Rough air underneath
Vertical Development
• Cumulonimbus (Cb)
– High, heavy masses going above freezing level
– Usually hail inside cloud, heavy rain/snow beneath
– Very turbulent
Sky Condition
• Cloud cover broken down into oktas (8ths):
–
–
–
–
–
Clear
Few
Scattered
Broken
Overcast
0
1-2
3-4
5-7
8
• Broken and Overcast considered a Ceiling
Cloud Formation
• Clouds form from condensation or sublimation
(water vapour to water droplets or ice). This
requires:
– High relative humidity
– Condensation nuclei
– Cooling air
• Formed in two ways:
– Air cools to saturation point (most common, by
expansion)
– Air absorbs water vapour to reach saturation point
Lifting Processes
• Clouds created when air rises, expands,
cools, condenses. Following processes force
air up:
–
–
–
–
Orographic Lift – Air forced up by hills/mountains
Convection – Sun heats ground, warm air rises
Frontal Lift – Warm air forced up over cold front
Turbulence – Wind blowing over rough ground
creates eddies, forcing up and down currents
– Convergence – Air inside a low pressure area is
forced upwards
Next Lesson
4.3 – Meteorology
Pressure
From the Ground Up
Chapter 6.3:
Pressure
Pages 127 - 130