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Why does a plane shake while passing through the clouds?

During my last journey all the other passengers started shouting when the plane was passing through clouds. It was the third time I was travelling by plane and was a fearful experience. Can someone explain what the reason is for the shaking? So the next time I can travel free of fear.

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    $\begingroup$ I disagree that this is a duplicate. The answer is not just turbulence, but how clouds are related to turbulence. Clouds are not mentioned in either of the answers to the other question. $\endgroup$
    – fooot
    Jul 10, 2017 at 21:49
  • $\begingroup$ The other question is clearly not a duplicate of this one... $\endgroup$
    – Daniele Procida
    Aug 26, 2017 at 18:45

2 Answers 2

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In a word, it's called "Turbulence" and in cloud, it is caused by differing air density.

Sciencey bit: The sun warms the earth and causes the air to rise. As warm air rises, it cools at the wet adiabatic lapse rate. Inside of a cloud, this rate is much slower than outside of it. Clouds are more dense than dry air, and the water vapour inside a cloud is not spread out evenly. Combined with the thermal turbulence (the movement of warm air) and the lower wet adiabatic lapse rate (rate of cooling) results in drafts of air through the cloud.

The result to the aircraft is pockets of more and less lift on the wings in somewhat unpredictable patterns. You feel this inside the aircraft as bumpiness and occasional feelings of rising or dropping. Sometimes this can be quite pronounced - this is why you will almost certainly be asked to remain seated with seatbelts fastened.

Very occasionally, outside of clouds, there can be more unpredicatable turbulence which may come as a surprise to the Pilot. This type of turbulence can cause injuries - usually from falling luggage or persons. This is why, even during cruise, the cabin crew and pilot usually suggest you keep your belt on while seated.

In almost no case does any kind of turbulence cause any damage to the aircraft or significantly affect its airworthiness.

Another answer here might be interesting reading for you How dangerous was the turbulence on this commercial flight? as might What is turbulence, and how does it happen?

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    $\begingroup$ Not all clouds cause turbulence. Flying through stratus clouds is generally very smooth. $\endgroup$
    – Mike Sowsun
    Jul 10, 2017 at 11:09
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    $\begingroup$ @MikeSowsun yes, of course you're right. But you could end up caveating every sentence with "except in this case". I was going for the simple explanation. The linked answers are much more detailed. $\endgroup$
    – Jamiec ♦
    Jul 10, 2017 at 11:13
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    $\begingroup$ This is a good answer, but I think @TechMedicNYC is also correct. I've also noticed high frequency vibration of aircraft perfectly correlated with entering and exiting a dense cloud that feels very different from convection turbulence. $\endgroup$
    – Devil07
    Jul 10, 2017 at 15:29
  • $\begingroup$ @Mike Sowsun: And conversely, you can encounter turbulence when not in clouds - indeed, in a perfectly clear sky. $\endgroup$
    – jamesqf
    Jul 10, 2017 at 17:16
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    $\begingroup$ you should not remark in the answer that the Q should be closed-as-dupe. Just flag it and let the reviewers vote. There is no demerit in asking a duplicate question. We flag them because it is useful to link the questions, makes the knowledge base more searcheable and saves effort on answers because there is already one. I've already cast my vote to close as duplicate. $\endgroup$
    – Mindwin Remember Monica
    Jul 10, 2017 at 17:18
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I'm not an expert, but I have a background in mechanical engineering.

I don't believe the turbulence answer is correct for all cases. Yes, turbulence causes shaking and yes, most clouds will contain more turbulence due to thermal effects, updrafts, downdrafts, etc...

However, I'm more inclined to believe the phenomenon the OP is asking about has to do with the density of the medium. The cloud contains cooler air, with suspended liquid droplets. This air should contain more mass per unit volume (that is, higher density fluid). This changes the amount of lift experienced as the plane passes through it. This would produce sudden changes in the amount of lift, causing shaking when entering or exiting the clouds. Furthermore, the clouds are not of uniform density. Pay attention as the plane enters and exits the cloud, you will notice the amount of "cloudiness" varies. This means the plane will be passing through air of varying density while in the cloud, causing the "bumpiness" of the ride.

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