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You’re soaring towards a fluffy 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?
Clouds Indicate Unstable Air
You can envision clouds as localized pockets of saturated air where the temperature of the air is equal to or lower than the dew point. 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 it is sufficiently cooled, the relative humidity becomes 100% and the temperature matches the dew point.
Here’s a fun way to think about it… Scientists have measured the water density of a typical fair-weather cumulus cloud to be 1/2 gram per cubic meter. Let’s say that cloud is 1 kilometer wide and 1 kilometer tall, which is quite typical for some cumulus clouds. If you do the math, that’s 1 billion cubic meters in volume, resulting in 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 from that of the surrounding air. That’s one reason why you might experience turbulence when flying through a cloud.
But another, and often more significant, reason turbulence occurs in clouds is due to the unstable mixing of air due to temperature, pressure, and velocity changes within clouds compared to the outside air. The difference in these factors between an air parcel inside versus outside a cloud determines how much turbulence you’ll encounter. Clouds can serve as a skyward signpost indicating 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 numerous reasons why turbulence forms, but the severity of windshear is arguably the most crucial factor. As you ascend to cruise altitude, you’ll fly through layers of air with varying densities, wind speeds, and temperatures. How the air mixes between layers determines whether you’ll feel turbulence or not. If the mixing is smooth and spread out over thousands of feet or even miles, you might not experience much turbulence at all, and you may notice the nose of the airplane gradually sway 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 increasingly stronger turbulence. Short shear areas generally create “chop,” while longer shear areas generally cause turbulence.
You can think of the turbulence when entering a cloud deck in the same way, as mild windshear.
Climbing Above a Temperature Inversion
Have you ever noticed that if you can ascend above a haze layer or fly just above the tops of scattered cumulus clouds, the ride is much smoother? 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 refer to this as 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 crystal clear above a temperature inversion. Clouds sitting at these boundaries are clear signs that you’re about to fly into a bumpy shear area.
Convection Within Clouds
There are strong updrafts and downdrafts embedded within cumulonimbus and cumulus clouds, unlike stratocumulus and nimbostratus clouds, which have lighter wind currents. When clouds produce showery precipitation, light, moderate, or greater turbulence can 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 bring intense convective turbulence both within and around the cloud.
But Why Are Some Clouds Totally Smooth?
You’re approaching what you think will be a turbulent cloud. It’s a few thousand feet tall, white, and fluffy, but when you fly through it, you feel almost nothing. Why?
Clouds can occasionally form in stable air that is relatively free from disturbance. Turbulence almost always occurs when different air masses mix. But when there’s a uniform air mass, the mixing won’t be strong 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 indications that the clouds around you will have little to no turbulence.
What Do You Think?
What tips have you learned over time to find the best flights in the sky? Leave a comment below.
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