Why You Experience Turbulence When Flying Through A Cloud

You're flying toward a puffy cumulus cloud and out of habit, your natural instinct is to tighten your seatbelt. It may seem like a simple question, but have you ever wondered why clouds can be so bumpy?

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Clouds Indicate Unstable Air

You can think of clouds as localized zones of saturated air, where the temperature of the air is at or below the dewpoint. Clouds will form whenever the amount of moisture in the air is such that the humidity reaches 100%. As a parcel of unsaturated air cools, its relative humidity increases. If sufficiently cooled, the relative humidity becomes 100% and the temperature equals the dew point.

Here's a fun way to think of it... Scientists have measured the water density of a typical fair-weather cumulus cloud as 1/2 gram per cubic meter. Let's say that cloud is 1 kilometer wide and 1 kilometer tall, which is pretty typical for some cumulus clouds. If you do the math, that's 1 billion cubic meters in volume for a weight of 1.1 million pounds (or roughly 100 elephants).

Why go through this random explanation? Simply put, the density of clouds is different than the surrounding air. That's one reason why you could experience turbulence when you fly through a cloud.

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But another, and often more significant, reason turbulence occurs in clouds is due to the unstable mixing of air due to the temperature, pressure, and velocity changes within clouds compared to the outside air. The difference in these factors between an air parcel within vs. outside a cloud determines how much turbulence you'll experience. Clouds can give you a signpost in the sky marking the location of turbulence and hazardous weather conditions. They can mark frontal passages, mountain wave activity, thermals, temperature inversions, and more.

The Severity Of Turbulence Is Determined By The Size Of The Shear Area

There are plenty of reasons why turbulence forms, but the severity of windshear is arguably the most critical factor. As you climb to cruise altitude, you'll fly through layers of air with different densities, wind speeds, and temperatures. How the air mixes between layers determines if you'll feel turbulence or not. If the mixing is smooth and spread out over thousands of feet or even miles, you might not feel much turbulence at all and you may see the nose of the airplane gradually swing towards the direction of the prevailing wind. If the shear area decreases in size (or increases in velocity) over a confined area of a few dozen or a few hundred feet, there's a recipe for incrementally stronger turbulence. Short shear areas generally create "chop" and longer shear areas generally create turbulence.

You can think of the turbulence when entering a cloud deck the same way, as mild windshear.

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Climbing Above A Temperature Inversion

Have you ever noticed that if you can outclimb a haze layer or fly just above the tops of scattered cumulus clouds that the ride is much more smooth? This is especially apparent in the summer and is sometimes caused by a temperature inversion, where a layer of warm air sits on top of cooler air below. Some people call this a "capping inversion" when you can physically see the "cap" of the haze layer around you.

Depending on the temperature and dew point spread between atmospheric layers, it's often perfectly clear above a temperature inversion. Clouds sitting at these boundaries are tell-tale signs that you're about to fly into a bumpy shear area.

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Convection Within Clouds

There are strong updrafts and downdrafts embedded within cumulonimbus and cumulus clouds, as opposed to stratocumulus and nimbostratus clouds which have lighter wind currents. When clouds generate showery precipitation, light, moderate, or greater turbulence should be expected. Generally speaking, the stronger the radar echo, the stronger the downdraft.

The most dramatic example of this would be, of course, thunderstorms. Towering cumulus, cumulonimbus, and thunderstorms almost always equal strong convective turbulence both in and around the cloud.

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But Why Are Some Clouds Are Totally Smooth?

You're flying towards what you think will be a turbulent cloud. It's a few thousand feet tall, white, and puffy, but when you fly through it you feel almost nothing. Why?

Clouds can occasionally form in stable air that's relatively free of disturbance. Turbulence almost always happens when differing air masses mix. But when there's a uniform air mass, mixing won't occur strongly enough to cause turbulence. If you can find extremely stable, saturated air, you'll find plenty of clouds without turbulence. Low lapse rates, constant temperatures, and low wind speeds are also great signs that clouds around you will have little to no turbulence.

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