Clear Air Turbulence Explained

Clear-air turbulence can turn an apparently calm cruise into a rough ride with little visual warning.

There may be:

• No thunderstorm ahead
• No heavy precipitation
• No obvious cloud boundary
• Nothing unusual on conventional weather radar

Yet the airplane can suddenly encounter rapidly changing airflow.

That is the operational challenge of clear-air turbulence, or CAT.

CAT is primarily a high-altitude turbulence problem associated with atmospheric wind shear and instability, especially around jet streams, upper-level fronts, and the tropopause.

But several common explanations are too simple.

CAT does not mean:

• Every encounter occurs in a perfectly cloudless blue sky.
• Every jet stream is turbulent.
• Wind shear and turbulence are the same thing.
• CAT occurs only above FL350.
• Weather forecasting cannot anticipate it.
• Pilots always escape it by changing altitude.
• Every airplane should slow to exactly maneuvering speed.

The useful mental model is:

strong wind shear + insufficient atmospheric stability → shear instability → turbulent eddies

Understanding that relationship explains both why CAT is difficult to see and why modern forecasting can still identify where it is more likely.

For the broader turbulence picture—including convection, mechanical turbulence, mountain waves, wake turbulence, and FAA intensity categories—start with What Is Turbulence?.

What Is Clear-Air Turbulence?#

Clear-air turbulence, or CAT, is turbulence not primarily associated with convective cloud such as thunderstorms.

FAA terminology commonly associates it with:

• High altitude
• Strong wind shear
• Jet-stream environments
• The vicinity of the tropopause

It is particularly important to jet aircraft cruising in the upper troposphere and lower stratosphere.

Does CAT Have to Occur in Completely Cloudless Air?#

Not always in the literal everyday sense.

The name clear-air turbulence suggests perfectly blue, cloud-free sky.

FAA operational definitions often describe CAT as turbulence where no clouds are present.

But FAA weather guidance also discusses CAT:

• In cirrus
• Within or near standing lenticular clouds
• In some clear-air regions near thunderstorms

The more useful distinction is therefore:

CAT is nonconvective, primarily high-altitude turbulence—not simply "turbulence under a perfectly blue sky."

That matters because a pilot should not conclude that thin high cloud automatically means a rough-air encounter is no longer CAT.

CAT Is a Type of Turbulence, Not an Intensity#

CAT describes where and how turbulence forms.

It does not tell you how strong the encounter will be.

CAT may be reported as:

• Light
• Moderate
• Severe
• Extreme

Those are turbulence intensity categories.

So: moderate CAT

means: clear-air turbulence of moderate intensity.

The same distinction applies to other turbulence mechanisms.

For example, mountain-wave turbulence or convective turbulence can also vary greatly in intensity.

CAT and Wind Shear Are Not the Same Thing#

Wind shear is a change in wind speed or direction over distance.

CAT is turbulent atmospheric motion.

The distinction matters because a shear layer can exist without becoming turbulent.

Imagine two layers of air moving at different velocities.

That difference creates shear.

Whether that shear breaks down into turbulent eddies depends partly on how strongly atmospheric stratification resists vertical displacement.

So the more complete chain is:

wind shear → possible dynamic instability → turbulence

rather than:

wind shear = turbulence

Vertical and Horizontal Wind Shear#

CAT can be associated with both:

• Vertical wind shear
• Horizontal wind shear

Vertical wind shear means wind changes substantially with altitude.

Horizontal shear means wind changes significantly across horizontal distance.

Both can occur around upper-level jet structures.

This is why simply drawing a fast jet-stream core beside slower surrounding air does not capture the entire CAT mechanism.

The atmosphere is three-dimensional.

Atmospheric Stability Matters#

Imagine two air layers moving at different speeds.

Strong shear tends to promote turbulent mixing.

Stable atmospheric stratification tends to resist vertical displacement.

CAT becomes more likely when the shear is strong enough to overcome that stabilizing influence.

Meteorologists describe this competition using quantities such as the Richardson number.

Richardson Number#

The gradient Richardson number, usually written Ri, compares atmospheric stratification with vertical wind shear.

Conceptually:

• Larger stabilizing stratification tends to increase Ri.
• Stronger vertical shear tends to decrease Ri.

Classical fluid theory identifies approximately:

Ri < 0.25

as a condition in which shear flow can become dynamically unstable.

That number is useful.

But it should not be turned into: "At 0.249 there is turbulence, and at 0.251 the air is smooth."

The real atmosphere is more complicated.

Local waves, model resolution, transient flow, existing turbulence, and other processes affect what actually happens.

So Ri ≈ 0.25 is best understood as a classical instability criterion, not a cockpit turbulence switch.

Kelvin–Helmholtz Instability#

One process by which strong shear becomes turbulence is Kelvin–Helmholtz instability.

Imagine faster air moving above slower air.

A small disturbance forms along the interface.

If atmospheric stability cannot suppress it, the disturbance can amplify into rolling waves.

Those waves can overturn and break.

The resulting flow becomes turbulent.

This mechanism helps explain how apparently smooth, cloud-free air near a strong shear zone can suddenly contain turbulent patches.

Why CAT Comes in Patches#

A jet stream hundreds or thousands of miles long is not continuously turbulent everywhere.

CAT often forms in relatively localized regions where the combination of:

• Shear
• Stability
• Atmospheric waves
• Temperature gradients
• Jet-stream structure

is favorable.

An aircraft can therefore spend a long time in smooth air, encounter several minutes of rough turbulence, and then return to smooth conditions without leaving the general jet-stream environment.

CAT is a patchy atmospheric process.

The Jet Stream Connection#

The jet stream is one of the most important environments for CAT.

Jet streams are narrow bands of very strong upper-level winds.

But a common statement needs correcting: "The strongest turbulence is in the middle of the jet stream."

Not necessarily.

A fast, uniform airflow can be smooth.

CAT is more closely associated with strong gradients and unstable shear around jet-stream structures.

FAA guidance identifies several particularly favorable areas.

The Poleward Side of the Jet#

For jet-associated CAT, FAA weather guidance says turbulence is frequently found on the poleward side of the jet stream.

Over the United States, that generally corresponds to the left side when looking downstream along the jet.

That is a useful forecasting clue.

It is not a guarantee.

An aircraft can encounter CAT elsewhere around the jet depending on the larger atmospheric pattern.

Jet Maxima and Jet Streaks#

A jet stream is not equally fast along its entire length.

Regions of locally stronger wind move through the larger jet structure.

These are often called jet maxima or jet streaks.

The acceleration and deceleration regions surrounding them can create strong:

• Horizontal shear
• Vertical motion
• Temperature advection
• Changes in atmospheric stability

CAT probability can therefore increase around these dynamically active portions of the jet.

The Tropopause Connection#

The tropopause separates the troposphere below from the stratosphere above.

Jet streams are commonly found near this boundary.

CAT associated with jets is also frequently found near the tropopause.

That does not mean: "The tropopause itself causes turbulence."

Instead, the atmospheric structure near:

• Jet streams
• Upper-level fronts
• Sloping tropopause regions
• Strong temperature gradients

can create the shear and stability conditions favorable for turbulence.

CAT Is Not Restricted to FL350 and Above#

The old rule: "CAT mostly occurs above FL350 between 35,000 and 45,000 feet"

is too restrictive.

FAA guidance describes CAT as normally a high-altitude phenomenon, particularly above about 15,000 feet.

It becomes especially operationally important to jet traffic at cruise altitude.

But CAT is not bounded by one flight-level range.

The location of favorable shear depends on:

• Latitude
• Season
• Jet-stream altitude
• Tropopause height
• Synoptic weather pattern

A CAT guide should therefore teach atmospheric structure rather than one memorized altitude band.

Upper-Level Fronts and Troughs#

CAT is also associated with upper-level frontal and trough patterns.

These environments can contain strong:

• Temperature gradients
• Wind gradients
• Jet-stream curvature
• Vertical shear

FAA guidance highlights portions of deep upper troughs where CAT is commonly found, especially around strong temperature advection and horizontal wind shear.

This connects CAT to the broader atmospheric systems covered in Air Masses & Fronts in Aviation.

CAT Is Not Only a Jet-Stream Phenomenon#

Jet streams are one of the most important CAT environments.

They are not the only one.

High-altitude turbulence can also be promoted by:

• Upper-level fronts
• Atmospheric-wave breaking
• Strong non-jet shear
• Tropopause structure

This is why the statement: "The jet stream causes most CAT"

is less useful than understanding the underlying mechanism.

The real cause is unstable atmospheric flow, often associated with strong shear.

Gravity Waves#

Gravity waves are oscillations that form when displaced air is restored toward its equilibrium level by buoyancy.

They can be generated by:

• Mountains
• Frontal systems
• Convection
• Jet-stream dynamics

Gravity waves themselves can be smooth.

But if they become sufficiently steep, they can break.

Wave breaking can locally increase shear and reduce atmospheric stability enough to generate turbulence.

CAT Versus Mountain-Wave Turbulence#

This distinction deserves care.

Stable airflow crossing mountains can produce atmospheric gravity waves.

Those waves may extend to airline cruise altitude and can exist in clear air.

Historically, some broad discussions of CAT include turbulence associated with standing lenticular and high-level wave environments.

Modern forecasting products, however, commonly distinguish:

• Clear-air turbulence
• Mountain-wave turbulence

as separate forecast mechanisms.

That distinction is useful.

CAT is typically associated with upper-level shear and dynamic instability.

Mountain-wave turbulence originates from airflow interacting with terrain and subsequent wave behavior.

They can overlap geographically and both can be invisible.

They should not simply be treated as the same thing.

CAT Versus Convective Turbulence#

Convection produces turbulence through buoyant vertical motion.

Thunderstorms can contain violent turbulence.

But thunderstorm turbulence is not what pilots ordinarily mean by CAT.

CAT is generally classified separately from turbulence produced directly by cumuliform convection.

This matters operationally because the detection and avoidance tools differ.

Strong convective weather may produce obvious:

• Clouds
• Lightning
• Precipitation
• Weather-radar returns

CAT often does not.

CAT Versus Wake Turbulence#

Wake turbulence is also different.

Wake turbulence is generated by another aircraft producing lift.

CAT is produced by atmospheric motion.

A rough encounter behind another aircraft at cruise altitude should therefore not automatically be attributed to CAT.

The source matters.

Why Conventional Weather Radar Cannot Show CAT#

Aircraft weather radar is extremely valuable for avoiding thunderstorms.

But conventional airborne weather radar primarily detects precipitation.

Dry CAT may contain:

• No rain
• No hail
• No significant cloud droplets

There may therefore be essentially nothing for conventional weather radar to reflect.

That is why a perfectly clean radar display does not guarantee smooth air.

"Radar Cannot Detect CAT" Also Needs Nuance#

The statement is true when talking about ordinary airborne precipitation radar.

It should not be generalized to every radar or remote-sensing technology.

Specialized research and ground-based systems can infer turbulence using techniques unavailable to normal cockpit weather radar.

FAA research, for example, uses radar-derived information for certain in-cloud turbulence products.

The practical pilot-facing rule remains:

do not expect standard airborne weather radar to show ordinary dry CAT ahead.

Can LIDAR Detect CAT?#

LIDAR uses laser light rather than radio waves.

Research systems have investigated whether changes in aerosol motion ahead of an airplane can reveal turbulent airflow before the aircraft enters it.

The concept is promising.

But forward-looking CAT LIDAR is not a universal, fleet-standard capability on today's commercial aircraft.

Operational CAT management still relies heavily on:

• Forecast models
• Aircraft observations
• Pilot reports
• Dispatch information
• ATC coordination

rather than a cockpit display that simply draws CAT cells ahead.

Forecasting CAT#

CAT is invisible, but it is not completely unpredictable.

Meteorologists can identify atmospheric structures favorable for it.

Forecast models evaluate variables such as:

• Wind shear
• Jet-stream structure
• Temperature gradients
• Atmospheric stability
• Deformation
• Wave activity

Different turbulence algorithms respond to different physical indicators.

Modern systems combine those algorithms rather than relying on one single CAT formula.

Graphical Turbulence Guidance#

Graphical Turbulence Guidance, or GTG, is one of the FAA's principal turbulence forecast systems.

GTG combines:

• Numerical weather prediction
• Multiple turbulence diagnostics
• In-situ turbulence observations

to produce forecast turbulence guidance.

The output is expressed using eddy dissipation rate, or EDR.

GTG3 and GTGG#

The FAA currently identifies:

• GTG3 as the operational CONUS version
• GTGG as the operational global version

GTG3 forecasts several mechanisms separately, including:

• Clear-air turbulence
• Mountain-wave turbulence
• Low-level turbulence

This is another reason CAT and mountain-wave turbulence should not simply be merged into one article concept.

What Is EDR?#

Eddy dissipation rate, or EDR, is a measure used to characterize turbulence intensity in the atmosphere.

Traditional turbulence reports are based partly on how one specific aircraft responds.

EDR provides a more objective description of the turbulent atmosphere itself.

That makes it valuable for:

• Automated aircraft observations
• Forecast verification
• Turbulence models
• Airline operational tools

Aircraft response still depends on aircraft characteristics.

So the same EDR does not necessarily produce an identical ride in every airplane.

Aircraft Size Still Matters#

FAA turbulence products account for aircraft weight class when translating EDR into operational turbulence categories.

A light airplane can respond differently from a heavy transport to the same turbulent atmosphere.

This is why: "A 747 and a regional jet enter the same air, so they feel exactly the same turbulence"

is wrong.

They encounter the same atmospheric disturbance.

Their physical responses may differ.

Automated Turbulence Observations#

Modern aircraft increasingly provide automated atmospheric turbulence observations.

These can include EDR measurements or estimates sent into meteorological data systems.

FAA turbulence forecasting uses observational inputs including:

• EDR reports
• AMDAR data
• PIREPs

to evaluate and weight forecast algorithms.

FAA research has also investigated deriving turbulence information from ADS-B vertical-rate data.

That is different from saying: "ADS-B itself is already the primary CAT sensor on every airliner."

It is not.

PIREPs#

PIREPs remain extremely valuable because they describe what an aircraft actually encountered.

FAA turbulence reports include information such as:

• Location
• Time
• Altitude or flight level
• Aircraft type
• Intensity
• Duration
• Whether the turbulence occurred in cloud or clear air

For CAT specifically, FAA guidance asks pilots to report:

• Time
• Location
• Intensity

as soon as practical.

Why Aircraft Type Matters in a PIREP#

Turbulence intensity in a conventional PIREP is partly based on aircraft reaction.

So an aircraft type is not optional trivia.

A light airplane reporting moderate turbulence does not guarantee that a heavy airliner will respond identically.

Likewise, a large aircraft's light-turbulence report should not automatically reassure the crew of a much smaller airplane.

Aircraft type gives the report context.

CAT Forecast Versus CAT Observation#

These two should never be confused.

Forecast#

A product such as GTG estimates where the atmosphere is likely to support turbulence.

Observation#

A PIREP or automated EDR report describes conditions an aircraft actually encountered.

A forecast can therefore indicate a high-risk area where a particular flight finds smooth conditions.

A PIREP can report turbulence where a coarse forecast did not resolve it.

Both sources are useful.

Neither is perfect.

G-AIRMET Tango#

In the contiguous United States, G-AIRMET Tango depicts broad areas where moderate nonconvective turbulence is forecast.

It identifies an area of concern.

It does not mean every point inside the polygon contains continuous moderate CAT.

And because it covers nonconvective turbulence generally, it is not synonymous with a CAT forecast.

SIGMETs#

A SIGMET can be issued for severe turbulence.

That is a more significant operational warning.

Again:

severity and mechanism are different dimensions.

A severe-turbulence SIGMET does not mean every turbulent region inside it is necessarily classic jet-stream CAT.

Significant-Weather Charts#

A SIGWX chart provides a broader strategic picture of significant weather at aviation altitudes.

For long-range and international operations, these products can help crews and dispatchers identify:

• Jet streams
• Turbulence regions
• Convective hazards
• Other major weather features

They are valuable for route planning but are not a substitute for current observations and shorter-range turbulence products.

Satellite Imagery#

Satellite imagery does not normally "see CAT" directly.

But it can help meteorologists understand the environment that creates it.

For example, satellite imagery can reveal:

• Jet-related cloud bands
• Upper-level moisture gradients
• Mountain-wave cloud structures
• Frontal patterns

Water-vapor imagery can be particularly useful for visualizing upper-level atmospheric structure.

These are indirect clues.

They are not direct measurements of turbulence intensity.

Why CAT Forecasting Remains Difficult#

CAT can exist on spatial scales smaller than the effective resolution of numerical weather models.

It can also:

• Form rapidly
• Dissipate rapidly
• Occur in narrow layers
• Vary strongly with altitude
• Depend on local wave breaking

A forecast can correctly identify a favorable broad environment and still miss the precise turbulent pocket encountered by an airplane.

That is why combining forecasts with real observations matters so much.

Can Pilots See CAT?#

Usually not directly.

There may be environmental clues such as:

• Jet-stream position
• Cirrus patterns
• Lenticular clouds
• Upper-level frontal structure

But there is no universal visual marker that tells the pilot: "The turbulence begins exactly here."

That invisibility is what makes CAT operationally challenging.

CAT and Aircraft Aerodynamics#

Turbulence changes the airflow arriving at the airplane.

A vertical gust can rapidly change the wing's effective angle of attack.

That changes lift.

The aircraft may therefore experience temporary changes in:

• Load factor
• Airspeed
• Pitch
• Roll
• Vertical acceleration
• Altitude

For the underlying aerodynamic response, see How Airplanes Fly.

CAT Does Not Mean the Aircraft Is "Falling"#

A rapid reduction in vertical acceleration can make passengers feel as though the airplane has suddenly dropped.

Human perception is extremely sensitive to acceleration.

So a dramatic stomach-dropping sensation does not directly tell you the altitude change.

Strong CAT can produce actual altitude excursions.

But felt motion and altitude loss are not the same measurement.

Severe CAT Can Affect Control#

CAT can occur at any FAA turbulence intensity.

In severe turbulence:

• Large abrupt altitude or attitude changes may occur
• Indicated airspeed may vary substantially
• The aircraft may be momentarily out of control

Extreme turbulence is still more serious and may produce structural damage.

CAT should therefore not be described as: "dangerous to passengers but never to the aircraft."

Most airline CAT encounters are well within the aircraft's operating capability.

The strongest categories still deserve genuine operational respect.

Why Seat Belts Matter#

For passengers, the most common serious CAT hazard is sudden acceleration while unrestrained.

A person who is not belted can be thrown:

• Upward
• Sideways
• Into the cabin interior
• Into another passenger

Cabin crew face particular exposure because their jobs require them to spend substantial time standing.

The simplest passenger protection remains:

keep your seat belt comfortably fastened whenever you are seated.

FAA turbulence-injury guidance specifically emphasizes restraint as one of the most effective protections.

CAT and Cabin Service#

Forecast turbulence often changes cabin operations before the aircraft reaches the rough air.

Crews may:

• Turn on the seat-belt sign
• Suspend service
• Secure carts
• Secure galley equipment
• Seat flight attendants earlier

The goal is not merely passenger comfort.

It is to avoid having unrestrained people and heavy equipment moving around when an abrupt acceleration arrives.

What Speed Do Pilots Use in CAT?#

There is no universal answer called:

"always slow to Va."

Maneuvering speed, V_A, is an important structural concept for many general aviation airplanes.

But CAT commonly affects transport aircraft operating at high altitude, where the operating problem includes:

• Mach number
• Buffet margins
• Aircraft weight
• Flight-control laws
• Manufacturer turbulence procedures

Aircraft manuals may specify a:

• Turbulence penetration speed
• Rough-air speed
• Recommended turbulence speed or Mach

The aircraft-specific value is the one that matters.

Why "Va Prevents Structural Damage" Is Too Simple#

V_A is not an invulnerability speed.

Its underlying design concept does not guarantee protection from:

• Every possible gust
• Repeated full control reversals
• Multiple-axis control inputs
• Every atmospheric load

And V_A changes with aircraft weight.

So the correct operational rule is:

use the aircraft's approved turbulent-air procedure, not a generic internet number.

Flying Too Fast in Turbulence#

Gust-induced loads generally increase with airspeed.

Reducing speed can therefore reduce structural loading in rough air.

That is why turbulence procedures often involve a lower operating speed.

But slowing indiscriminately is not the goal.

The aircraft still needs adequate:

• Stall margin
• Buffet margin
• Control margin

especially at high altitude.

Transport-aircraft turbulence speeds are designed around that compromise.

Flying Too Slowly Is Not the Generic CAT Solution Either#

At high altitude, an aircraft may have less airspeed margin between:

• Low-speed buffet
• High-speed/Mach buffet

than it would at lower altitude.

Excessive deceleration can therefore create a different aerodynamic problem.

This is why the simple advice: "The slower the better in turbulence"

is wrong.

Autopilot Use in CAT#

There is no universal rule that the autopilot must always be disconnected during CAT.

Different aircraft have very different:

• Autopilot logic
• Flight-control laws
• Load-alleviation systems
• Turbulence modes
• Operating procedures

Some procedures may call for remaining coupled.

Others may call for changing modes or disconnecting automation under specific conditions.

The aircraft flight manual and operator procedure determine the correct response.

Altitude Hold and Turbulence#

A pilot or autopilot attempting to correct every small altitude displacement can require additional control activity.

In some turbulent-air procedures, the goal is therefore not to chase the altimeter aggressively.

Temporary altitude and airspeed deviations may be preferable to unnecessarily large control inputs.

But that is not a universal instruction to disable altitude hold on every airplane.

Again, aircraft-specific procedures control.

Why Changing Altitude Can Help#

Turbulent layers may be relatively shallow.

Climbing or descending a few thousand feet can sometimes move the aircraft into smoother air.

This is why pilots often ask ATC: "How are the rides at another flight level?"

Reports from aircraft above and below can reveal whether a better altitude exists.

Why Changing Altitude Does Not Always Work#

A CAT region can also be:

• Deep
• Sloping
• Evolving
• Present at several adjacent levels

Traffic may prevent an immediate altitude change.

The aircraft may also be limited by:

• Performance
• Maximum altitude
• Fuel efficiency
• Weather at another level

Sometimes a lateral deviation is more effective.

Sometimes the crew simply reduces speed and waits for the patch to end.

There is no universal CAT escape maneuver.

Route Planning and Dispatch#

Airline CAT management begins long before passengers board.

Dispatchers and crews can consider:

• GTG
• G-AIRMETs
• SIGMETs
• PIREPs
• Automated EDR observations
• Jet-stream location
• Route options
• Flight levels
• Fuel implications

The flight plan may be adjusted around a broad forecast area.

Later, real-time observations can trigger another change.

This is an iterative process.

Why Pilots Cannot Avoid Every CAT Area#

Avoiding every region where turbulence is merely possible would be operationally unrealistic.

Forecast polygons and model guidance often cover enormous areas.

Many of those areas contain:

• Smooth sections
• Light turbulence
• Localized stronger patches

Crews therefore manage CAT based on:

• Expected severity
• Aircraft capability
• Passenger safety
• Observations
• Route and altitude alternatives

The objective is risk management—not a guarantee that nobody feels a bump.

Seasonality#

Jet streams and upper-level temperature gradients change seasonally.

In many Northern Hemisphere midlatitude regions, stronger wintertime jets can produce greater CAT potential.

But a Quick Fact such as: "CAT season is November through March"

is too geographically specific to treat as a global aviation rule.

Southern Hemisphere seasons are reversed, and CAT occurs year-round.

Season changes probability.

It does not turn CAT on and off.

Is Climate Change Increasing CAT?#

This question deserves a careful answer because two different kinds of evidence are often blended together.

There are:

1. Historical/reanalysis studies asking whether diagnosed CAT has already changed.
2. Climate-model studies asking how CAT may change in the future.

Those are not the same claim.

Evidence of Historical Increases#

A 2023 peer-reviewed study analyzed modern atmospheric reanalysis data from 1979 through 2020 using 21 CAT diagnostics.

It found substantial increases in diagnosed CAT at aircraft cruising altitudes in several midlatitude regions.

At an average North Atlantic point, the study estimated that between 1979 and 2020:

• Light-or-greater diagnosed CAT increased
• Moderate-or-greater diagnosed CAT increased more
• Severe-or-greater diagnosed CAT increased still more in relative terms

The reported relative increase for severe-or-greater CAT at that representative North Atlantic location was about 55 percent.

That is meaningful evidence of a historical trend.

But the wording matters.

The study analyzed reanalysis-based turbulence diagnostics.

It did not count every actual aircraft encounter over four decades.

Nor does it show that climate change caused any individual recent turbulence incident.

Future Climate Projections#

Separate climate-model studies have projected further CAT increases as greenhouse-gas concentrations rise.

A 2017 study of transatlantic wintertime CAT under a doubled-CO₂ climate simulated increases across:

• Light CAT
• Moderate CAT
• Severe CAT

with the largest relative increases in the stronger categories.

Another 2017 global study projected substantial regional increases by 2050–2080 under its climate scenario.

Those are model projections.

They should not be rewritten as: "Scientists have measured that severe CAT has already doubled everywhere."

They have not.

Why a Warmer Climate Can Increase CAT#

A warming atmosphere does not simply mean: "warmer air is more turbulent."

The mechanism is linked to atmospheric temperature gradients and upper-level wind shear.

Climate-model research indicates that changing temperature contrasts can strengthen certain vertical wind shears at cruise altitude.

Stronger shear can increase the prevalence of dynamically unstable conditions capable of generating CAT.

The expected changes vary by:

• Region
• Season
• Altitude
• Turbulence strength

There is no scientific basis for saying every route will become equally turbulent.

Climate Change Does Not Explain Every Turbulence Encounter#

Weather varies naturally from day to day and year to year.

One severe CAT event cannot by itself be attributed to climate change simply because long-term CAT risk is increasing in some regions.

The defensible conclusion is:

there is observational/reanalysis evidence that diagnosed CAT has increased in important regions over recent decades, and climate models project further increases under continued warming.

That is very different from:

every recent rough flight was caused by climate change.

Common Myths About Clear-Air Turbulence#

Myth: CAT always occurs in completely cloudless skies#

Not necessarily.

Despite the name, FAA weather guidance includes some high-altitude turbulence in cirrus and around standing lenticular clouds within CAT discussions.

The key distinction is from ordinary convective turbulence.

Myth: CAT only occurs above FL350#

No.

FAA guidance describes CAT as normally a high-altitude phenomenon, particularly above about 15,000 feet, but it is not limited to one cruise band.

Myth: The jet-stream core is always the roughest place#

No.

A fast but uniform airflow can be smooth.

Strong shear and instability around jet-stream structures are what matter.

Myth: Jet streams are the only source of CAT#

No.

Jet-associated shear is extremely important, but upper-level fronts, waves, tropopause structure, and other shear environments can also produce CAT.

Myth: Wind shear and CAT are the same thing#

No.

Wind shear is a wind gradient.

CAT occurs when atmospheric flow becomes turbulent.

Shear is one of the major ingredients.

Myth: Richardson number below 0.25 guarantees CAT#

No.

The value is a classical dynamic-instability threshold.

The real atmosphere and forecasting models are more complex.

Myth: Mountain-wave turbulence is simply CAT#

They can overlap and both may occur in apparently clear air, but modern forecast products distinguish CAT from mountain-wave turbulence because they have different primary mechanisms.

Myth: Weather radar should show severe CAT#

Ordinary airborne weather radar detects precipitation.

Dry CAT can produce no useful precipitation return.

Myth: CAT cannot be forecast#

It cannot be predicted at every exact point and second, but modern systems such as GTG can identify areas and altitudes where turbulence is more likely.

Myth: PIREPs are the only turbulence data available#

PIREPs remain valuable, but automated aircraft EDR observations are now an important part of the turbulence-data ecosystem.

Myth: Pilots always slow to Va#

No.

They use the turbulence or rough-air speed specified for the aircraft and operating condition.

Myth: Larger airplanes do not experience CAT#

They do.

Aircraft size changes the response to a given turbulent atmosphere; it does not make the atmosphere disappear.

Myth: CAT can hurt people but cannot affect the airplane#

Most airline encounters primarily create comfort and occupant-restraint issues.

Severe turbulence can momentarily affect control, and extreme turbulence may cause structural damage.

Myth: Climate change has already doubled CAT everywhere#

No.

Historical studies find substantial increases in diagnosed CAT in some regions, while climate models project additional future increases.

The magnitude varies by region, altitude, season, and turbulence category.

Frequently Asked Questions#

Key Takeaways#

• Clear-air turbulence is primarily high-altitude, nonconvective turbulence associated with atmospheric shear and instability.
• Despite its name, CAT does not have to occur in a perfectly cloudless blue sky.
• CAT is a turbulence type; light, moderate, severe, and extreme describe intensity.
• Wind shear and turbulence are related but are not the same phenomenon.
• Both vertical and horizontal wind shear can contribute to CAT.
• Atmospheric stability determines whether strong shear is able to break down into turbulent motion.
• A gradient Richardson number below roughly 0.25 is a classical shear-instability criterion, not an operational on/off switch for CAT.
• Kelvin–Helmholtz instability is one mechanism by which shear flow can overturn and become turbulent.
• Jet streams are major CAT environments, but the jet core itself is not automatically turbulent.
• FAA guidance frequently places jet-associated CAT on the poleward side of the jet and near jet maxima and tropopause structures.
• CAT is normally a higher-altitude phenomenon, often above about 15,000 feet, but is not limited to FL350–450.
• Upper-level fronts, troughs, tropopause structure, and breaking atmospheric waves can also favor CAT.
• Modern forecasting distinguishes clear-air turbulence from mountain-wave and low-level turbulence.
• Conventional airborne weather radar primarily detects precipitation and cannot provide a complete map of dry CAT.
• GTG combines numerical weather models, turbulence diagnostics, and observations to forecast turbulence in terms of EDR.
• GTG3 is the current operational CONUS version, while GTGG provides global guidance.
• PIREPs remain valuable observations, while automated EDR data provide increasingly objective turbulence measurements.
• Aircraft type matters because different aircraft can respond differently to the same turbulent atmosphere.
• Pilots use aircraft-specific turbulent-air penetration speeds and procedures rather than one universal Va rule.
• There is no universal CAT escape maneuver; altitude, lateral route, airspeed, traffic, performance, and fuel all matter.
• Most CAT encounters are manageable, but severe turbulence can momentarily affect aircraft control and extreme turbulence may cause structural damage.
• Seat belts remain one of the most effective protections against unexpected CAT injury.
• Historical reanalysis studies show CAT increases in several important regions, while climate models project further future increases.
• Historical trends, climate attribution, and future projections should be kept conceptually separate.
• Aircraft-specific manuals, operator procedures, current forecasts, and ATC/dispatch information always take precedence over generic CAT rules.

Sources & References#

• FAA Aviation Weather Handbook, FAA-H-8083-28B, Chapter 19: Turbulence.
• FAA Aeronautical Information Manual, current edition, Chapter 7: turbulence reporting and CAT PIREPs.
• FAA Pilot's Handbook of Aeronautical Knowledge, FAA-H-8083-25C, Chapter 12: Weather Theory.
• FAA Aviation Weather Research Program: Turbulence — GTG3, GTGG, EDR, automated turbulence observations, and forecasting research.
• FAA Aviation Weather Center — Graphical Forecasts for Aviation, turbulence guidance, G-AIRMETs, SIGMETs, PIREPs, and significant-weather products.
• FAA Advisory Circular AC 120-88A, Preventing Injuries Caused by Turbulence.
• American Meteorological Society Glossary of Meteorology — gradient and critical Richardson number.
• Prosser et al. (2023), "Evidence for Large Increases in Clear-Air Turbulence Over the Past Four Decades," Geophysical Research Letters.
• Williams (2017), "Increased Light, Moderate, and Severe Clear-Air Turbulence in Response to Climate Change," Advances in Atmospheric Sciences.
• Storer, Williams & Joshi (2017), "Global Response of Clear-Air Turbulence to Climate Change," Geophysical Research Letters.