In brief
- Clear air turbulence – or CAT – is turbulence that occurs in clear skies without a defined cause (like convective turbulence, orographic turbulence, etc.)
- CAT often occurs around the jet stream, where wind can change direction quickly, leading to turbulence
- It’s impossible to pinpoint CAT, but aviation-quality forecasts are improving, and flight planners and pilots will do what they can to avoid it
What is clear air turbulence and what causes it?
Clear air turbulence – CAT for short – is primarily caused by air movements around the jet stream.
The jet stream is a band of fast-moving air around the earth. It can reach incredible speeds. It exists at between 30,000 – 40,000 feet – exactly where commercial jets fly.
Pilots are aware of the jet stream and use it to their advantage, hitching a ride on it to save time – especially on transatlantic flights where the jet stream can be strong.
The core of the jet stream can often be smooth, but planes flying into, out of, and across the jet stream can all experience CAT.
CAT is also present at the polar side (north side) of the jet stream and in areas where the jet stream terminates.
The name suggests that CAT takes pilots by surprise, but it’s somewhat misleading. Since the discovery of the jet stream in WW2, meteorologists have made incredible progress in their ability to predict where the jet stream is – as well as map wind shear, the changing direction of the wind around the jet stream that can cause CAT.
Can you predict clear air turbulence?
The jet stream was discovered by pilots flying during WW2. Since then, we’ve learned a lot more about what the jet stream is and now have models that can predict where it is, but like all weather forecasts, it’s not 100% accurate.
We’ve written before about how commercial turbulence forecast apps like Turbli aren’t particularly accurate and how they can increase anxiety in some passengers.
If you’re interested, you can check out our turbulence forecasting tools page to get free access to the models that many of these websites and apps use.
While we can predict with some certainty where the jet stream is, and the behaviour of the wind around it, this doesn’t mean that we can predict turbulence with huge accuracy yet (despite what turbulence forecasting sites will tell you!).
Can pilots completely avoid CAT?
No, it’s impossible to avoid CAT entirely – but pilots and flight planners will do their best.
When flight plans are designed, the possibility of CAT will be taken into consideration. Pilots and flight planners know that turbulence is uncomfortable and will do everything they can to minimise it.
Of course, this isn’t always possible – but they will try.
When it comes to turbulence forecasting, pilots are in a better position than passengers.
As well as detailed turbulence forecasting systems they can get real-time information from other pilots while they’re in the air. If a plane ahead experiences turbulence, pilots may request a change of altitude (or be told to change by flight planners).
While it’s impossible to avoid CAT, the system will do everything it can to do so.
How much does the plane move during clear air turbulence?
In aviation, turbulence is graded into four levels (light, moderate, severe and extreme).
These terms don’t define how much the plane moves up and down, but the reaction of the plane to the turbulence – and that ability of the pilots to stay in control.
Light turbulence is likely on all flights. Moderate turbulence is less common but can be expected in flight (especially on some turbulent routes, including the transatlantic flight path).
Severe turbulence is very rare, with extreme turbulence incredibly rare.
The only people capable of grading turbulence accurately are pilots. Most passengers simply don’t have the experience – or access to the tools and systems that pilots do – to grade turbulence. (Most pilots politely suggest passengers routinely exaggerate the turbulence levels they experience.)
Returning to the original point. In light turbulence, the plane may move a few centimetres. Moderate turbulence may see the plane shift several metres. Severe turbulence may see the plane lose tens or even hundreds of metres.
It’s important to say that light, moderate and even severe turbulence aren’t dangerous to the plane. It will continue to fly. Passengers who aren’t strapped in may be in danger, so the advice is to always say lightly strapped in.
Is clear air turbulence dangerous?
Light and moderate turbulence may be uncomfortable, but they’re not dangerous.
Severe clear air turbulence can be dangerous, but it’s very rare and statistically unlikely that you will ever experience it.
If you follow the instructions of the crew and the pilots, stay in your seat and remain strapped in, even severe turbulence won’t harm you.
Can clear air turbulence crash a plane?
Lots of anxious fliers worry that clear air turbulence can crash a plane, but this is extremely unlikely, as modern airliners are built to withstand turbulence with modern airliners.
CAT may be uncomfortable, but it’s not unsafe.
It’s true that a pilot may momentarily lose control of the plane during severe turbulence, but such a situation is incredibly rare, and control is restored quickly as the plane continues to fly forward.
Why am I worried about CAT?
Turbulence is uncomfortable, especially if it appears out of nowhere like CAT. If you’ve experienced turbulence that appears in a clear sky, it can be stressful. Lots of anxious fliers (including me!) have experienced turbulent flights, and the impact is acute and lasting.
For anxious flyers, being worried about CAT is normal.
Anxious flyers want control of a situation and attempt to find that by trying to predict what their flights will be like. This includes looking at turbulence forecasts, jet stream forecasts, weather forecasts and more.
The reality is that CAT is almost impossible to predict with precision. When you fly, you give up control to others – including the pilot – and can’t plan for what will happen.
Instead of trying to predict CAT or plan for it, you need to accept the possibility for turbulence is always there. Instead of increasing anxiety, this can be liberating.
You can also learn about what causes turbulence and why you’re safe in our fear of flying guides. If you need some in-flight calm, check out the Help Desk and download the free Calm Flight Toolkit.
Please share this article with anyone who might benefit from it.
FAQs
Severe clear air turbulence is very rare, and most passengers will never experience it. While atmospheric conditions are changing, commercial aviation remains safe, and aircraft are engineered to withstand turbulence.
Turbulence often feels more intense because of your physical and emotional response to it. When your body is in a heightened state of anxiety, turbulence can be perceived as a greater threat than it actually is. By understanding the physics of flight and practicing grounding techniques you can reduce this fear.
While severe or extreme turbulence can theoretically cause issues, it is extremely rare for it to pose a danger to modern airliners. Pilots are trained to handle turbulence, and commercial aviation statistics confirm that flying remains one of the safest forms of travel.
If you are a nervous flyer, prepare before your flight by visiting our Help Desk for breathing and mindfulness exercises. If you experience turbulence in the air, focus on your breathing, stay strapped in, and remember that the movement is a normal part of flight
