What is clear air turbulence?

It is turbulence that happens without clouds to signal it, generally at or above 15,000 feet and often near the jet stream. Because it comes without visual clues, it is the main reason pilots ask you to keep your belt fastened even when the sky looks clear. It is still routine, and forecasts increasingly show where it is likely.

Why is it bumpy when we fly through clouds?

Because many clouds are the visible top of rising air. When cumulus clouds are present, the turbulent layer of rising air reaches from the surface up to the cloud tops, so the bump you feel and the cloud you see are the same rising motion. You are not hitting anything solid.

What does the jet stream have to do with turbulence?

The jet stream is a fast river of high altitude wind, and clear air turbulence is often found near it where fast and slow air meet. Pilots know where the jet stream is and can often change altitude to find smoother air above or below the roughest layer.

How do pilots know where turbulence is?

They use automated forecasts like the Graphical Turbulence Guidance, official advisories called SIGMETs and AIRMETs, and real time reports from aircraft flying ahead of them. Together these let a crew find the smoothest ride and prepare for the bumpier air before you ever feel it.

What do light, moderate, and severe turbulence mean?

They are defined by what happens inside the airplane, not by fear. In light turbulence loose objects stay at rest. In moderate you feel definite strain against your belt but the airplane is fully controlled. Severe, which is rare and brief, throws unsecured occupants against their belts. The airplane handles all of it.

Turbulence, explained

Why Does a Plane Shake? What Actually Causes Turbulence

Turbulence is the plane flying through uneven air: heat off the ground, wind over mountains, jet streams, and aircraft wakes. Here is what each one is, and how pilots forecast it.

Turbulence is simply the airplane flying through air that is moving unevenly, and only a handful of things stir the air up. Heat rising off the ground, wind tumbling over mountains, the fast high altitude rivers of air called jet streams, and the wake of other aircraft. None of them mean anything is wrong with the airplane, and all of them are things pilots forecast and plan for every day.

The four things that cause bumps

The first is convective, or thermal, turbulence. On warm days the sun heats the ground unevenly and sends up rising columns of air, which on a hot afternoon can build into thunderstorms. This is the bumpiness of a summer climb out.

The second is mechanical turbulence, from friction between the air and the ground, especially irregular terrain. Its strongest form is the mountain wave, the turbulent eddies found downwind of a ridge, which produce some of the most severe mechanical turbulence. It is why a flight can get bumpy crossing the Rockies on an otherwise clear day.

The third is clear air turbulence, or CAT, which is turbulence not associated with clouds, occurring at or above 15,000 feet, and not restricted to cloud free air. It tends to be found near the jet streams, and it is the tricky one because it is often encountered unexpectedly and without visual clues to warn pilots. That is why the seat belt sign sometimes comes on when the sky outside looks perfectly clear.

The fourth is wake turbulence, which every airplane makes just by flying. Lift creates two counter rotating vortices trailing behind the wingtips. Air traffic control spaces airplanes to keep clear of it, so it is mostly something you might feel briefly on approach behind a larger jet.

Why clouds mean bumps

A puffy fair weather cloud is the visible top of a column of rising warm air, a bit like steam over a pot. When cumulus or larger clouds are present, that turbulent layer of rising air extends from the surface all the way up to the cloud tops. Flying through it, the bump you feel and the cloud you see are the same event.

How turbulence is measured and forecast

Pilots do not rate turbulence by how scary it feels. They rate it by what the airplane does. The FAA's reporting criteria run from light, where loose objects stay at rest, to moderate, severe, and extreme. Modern forecasts turn that into a single number called the eddy dissipation rate, or EDR, which runs from close to 0 for smooth air to near 1 for the most extreme.

That number is not guesswork. The Graphical Turbulence Guidance forecast is generated automatically from aircraft observations and weather model data and expressed as EDR. It is the same family of data the forecast behind this tool is built on, which is why our route checker can tell you in plain language what a given flight is likely to feel. Pilots also get advisories such as SIGMETs and AIRMETs describing hazardous weather en route, plus reports from other aircraft ahead of them.

Two ways to picture it

Clear air turbulence is wind shear you cannot see, where two layers of air slide past each other at different speeds, like the choppy seam where a fast river current meets slower water. Most of it happens in clear sky, which is exactly why a smooth looking day can still have a bumpy stretch at altitude.

A bump in a cloud is not the airplane hitting something solid. Clouds have no substance to hit. You are feeling the same rising air that made the cloud visible in the first place, the way you would feel a warm updraft if you walked from shade into sun.

If you are a nervous flier

Not knowing why the airplane is shaking is its own kind of fear. Once you can name it, warm air rising, wind spilling over a ridge, the seam of a jet stream, the bump stops being a mystery and becomes weather, the same as rain on a windshield. It is uncomfortable, it is temporary, and it is one of the most studied and carefully forecast parts of the entire flight.

If you would like to talk it through

If reading the numbers helps but you would still like to hear it from a person, you can book a one on one call with a real airline pilot at Dial A Pilot. And before your next flight, you can check the turbulence forecast for your exact route in plain language.

Sources

Last reviewed July 17, 2026. These pages are built from primary sources and reviewed as those sources change.

Frequently asked questions

What is clear air turbulence?: It is turbulence that happens without clouds to signal it, generally at or above 15,000 feet and often near the jet stream. Because it comes without visual clues, it is the main reason pilots ask you to keep your belt fastened even when the sky looks clear. It is still routine, and forecasts increasingly show where it is likely.
Why is it bumpy when we fly through clouds?: Because many clouds are the visible top of rising air. When cumulus clouds are present, the turbulent layer of rising air reaches from the surface up to the cloud tops, so the bump you feel and the cloud you see are the same rising motion. You are not hitting anything solid.
What does the jet stream have to do with turbulence?: The jet stream is a fast river of high altitude wind, and clear air turbulence is often found near it where fast and slow air meet. Pilots know where the jet stream is and can often change altitude to find smoother air above or below the roughest layer.
How do pilots know where turbulence is?: They use automated forecasts like the Graphical Turbulence Guidance, official advisories called SIGMETs and AIRMETs, and real time reports from aircraft flying ahead of them. Together these let a crew find the smoothest ride and prepare for the bumpier air before you ever feel it.
What do light, moderate, and severe turbulence mean?: They are defined by what happens inside the airplane, not by fear. In light turbulence loose objects stay at rest. In moderate you feel definite strain against your belt but the airplane is fully controlled. Severe, which is rare and brief, throws unsecured occupants against their belts. The airplane handles all of it.