How to Read Clouds (and Flight Conditions) According to an Air Canada Captain


There’s a wondrous story unfolding just outside your airplane window.

Without clouds, our weather would be devoid of rain, snow, hurricanes, monsoons, fog and, of course, rainbows. Although moisture accounts for a measly zero to four percent of our atmosphere, it’s enough to create these signposts of weather, which is why I’m always scanning the sky for hints on ride conditions: Clouds are exciting reads.

For example, daytime heating causes air to rise and condense, creating puffy cumulus clouds that, as time–lapse photography reveals, last from five to 50 minutes but are constantly reforming. It’s no wonder these cloud formations indicate a bumpy ride until we fly above them. Layered clouds usually promise smooth flying. Clouds can also cause ice to form on aircraft and reduce visibility near the ground. Fog, a ground–based cloud, occurs via six different atmospheric processes, such as heat escaping the ground on a clear night (radiation fog) or warm air moving over a cool surface (advection fog, like you see over San Francisco Bay). But fog rarely stops us from taking off or landing. Even high clouds, composed primarily of ice crystals forming aft of our jet engines (a.k.a. contrails), can foreshadow advancing weather when they take longer than usual to disperse. A mackerel sky (clouds that resemble a fish’s scales) is a high–altitude cirrus cloud called cirrocumulus, which signals potential bumps from a fast–moving jet stream.

Related: How Do Airplane Wings Work?

By learning about clouds, you are indirectly learning how to read flight conditions. The standard cloud chart only has nine columns. The cloud cumulonimbus, found in column nine, is where the expression “on cloud nine” stems from. A weather oxymoron, this billowy, cotton–batting–like cloud looks soft and cute, but pilots know to avoid it – these clouds can grow to over 50,000 feet in altitude, so airliners can’t fly over them. While we usually hope for clear skies, clouds are a lot more interesting.

September 20 2021


Infographic explaining different cloud forms and styles
  • Meteorologists and pilots measure cloud cover in eighths, or oktas. A BKN (broken) layer of cloud ranges from 5/8 to just under 8/8. An OVC (overcast) layer is 8/8.

  • Clouds are composed of liquid water droplets, supercooled water droplets, ice crystals or all of the above.

  • Most cloud is trapped in the lowest layer of the atmosphere, called the troposphere. But you may see rare nacreous clouds formed by ice crystals high in the stratosphere.

  • The atmosphere may seem vast, but it’s tiny in Earth scale: Think of a basketball covered in morning dew.


In 1802, Englishman Luke Howard gave clouds the common names we use today: stratus, for layers of cloud much wider than they are thick; cumulus, for heaps of separated cloud masses with flat bottoms and cauliflower tops; and cirrus, for wispy curls of cloud seen high in the sky.

Related: How Does Flight Planning Work?

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Portrait of Air Canada's Captain Doug Morris
Photo: Reynard Li

Doug Morris is an author, meteorologist, instructor and Air Canada captain on the Boeing 787.