Clear-Air Turbulence: Why Radar Misses It

Clear-air turbulence, also written as clear air turbulence and usually shortened to CAT, is sudden, often severe shaking that happens in a cloudless sky, with no storm, no visible cloud and no warning on the weather radar in the cockpit. It happens because two masses of air moving at very different speeds are sitting right next to each other, and the boundary between them tears into small, chaotic eddies the way a fast river current does when it meets a slow one. Pilots cannot see it coming and, in the overwhelming majority of cases, neither can their instruments. That combination, invisible and instrument-blind, is the entire reason CAT feels sudden even though the atmospheric conditions that cause it can sit in place for hours.

How clear-air turbulence actually forms

CAT is defined by the US National Weather Service as turbulence "not associated with cumuliform clouds, including thunderstorms," occurring at or above 15,000 feet (NWS, "Turbulence," captured 2026-09-23). The mechanism underneath that definition is wind shear: a change in wind speed or direction over a short horizontal or vertical distance. When two neighbouring layers or pockets of air are moving at meaningfully different speeds, the friction between them destabilises the airflow, and the smooth motion breaks down into turbulent eddies, the same way smooth water breaks into whitewater where a fast current meets a slow one. The NWS training material notes that "when the change in wind speed and direction is pronounced, quite severe turbulence can be expected" (NWS, captured 2026-09-23), and that a typical CAT patch runs roughly 2,000 feet deep, 20 miles wide and 50 miles long, though patches as large as 10,000 feet thick and 1,000 miles long have been recorded.

Why the jet stream is almost always involved

Jet streams are narrow, fast-moving ribbons of air that sit near the altitude commercial aircraft cruise at, and they exist because of large temperature differences between neighbouring air masses. At the edges of a jet stream, the wind speed drops off quickly over a short distance, which is exactly the kind of shear that generates CAT. Wikipedia's entry on clear-air turbulence, citing aviation-meteorology research, notes that CAT most commonly occurs between roughly 23,000 and 39,000 feet, in the high troposphere near the tropopause, the boundary layer where the jet stream runs (Wikipedia, "Clear-air turbulence," captured 2026-09-23). Pilot Institute puts the practical range pilots plan around at Flight Level 200 to 450, and describes the same shear trigger in operational terms: turbulence becomes likely once vertical wind speed changes by roughly 5 knots per 1,000 feet, or horizontal wind speed changes by more than about 40 knots over 150 miles (Pilot Institute, "Clear Air Turbulence," captured 2026-09-23). Cruise altitude for a long-haul jet sits inside that same band, which is why CAT is a routine planning factor on long sectors rather than a rare event.

Why weather radar can't see it coming

The honest, slightly unsatisfying answer is that weather radar was never built to see this. Onboard weather radar works by bouncing a signal off water droplets and ice inside clouds and storms; it detects precipitation, not air movement. Clear-air turbulence, by definition, happens where there is no cloud and no precipitation for the radar beam to reflect off, so there is nothing for the radar to return an echo from. Thomas Guinn, a meteorology professor at Embry-Riddle Aeronautical University, called CAT "probably one of the most challenging forecast problems we have right now for aviation meteorology" (Global News, "Turbulence can strike in clear skies," captured 2026-09-23), and Pilot Institute confirms the same limitation for the newer alternatives: scintillometers and Doppler LIDAR units exist and can, in principle, detect the air-density fluctuations CAT causes, but Paul Williams of the University of Reading notes that specialised radar-like equipment able to make the turbulence visible is currently too heavy and too costly for routine airline use (Global News, captured 2026-09-23). Until that changes, there is no instrument on a typical commercial aircraft that flags CAT before the aircraft flies into it.

How pilots actually find out where it is

Since no onboard instrument reliably detects CAT in advance, the working solution is closer to crowd- sourcing than to sensing. A pilot who flies through rough air files a PIREP, a pilot report, noting the turbulence intensity (light, moderate, severe or extreme), the location, the altitude and roughly how long it lasted. Pilot Institute describes PIREPs as "the best source of information" available for tracking where CAT is happening as conditions develop (Pilot Institute, captured 2026-09-23), because every following aircraft on a similar route and altitude can be rerouted or descended around the same patch before it gets there. Forecasters also build turbulence-probability charts from jet-stream wind data and historical patterns, which is why a pilot might turn the seatbelt sign on over a specific stretch of ocean or continent even on a perfectly clear day: not because anything is visibly wrong outside the window, but because the forecast band and a recent PIREP line up with exactly the shear conditions this article describes.

Is clear-air turbulence getting more common?

There is a specific, sourced answer to this rather than a vague sense that flights feel bumpier. Paul Williams's own research, cited by Global News, projects "more clear-air turbulence in the future" as a consequence of how climate change is altering high-altitude wind patterns (Global News, captured 2026-09-23). The underlying study, Williams and Joshi (2013), modelled transatlantic wintertime CAT under a doubled-CO2 scenario and projected increases of roughly 60% for light turbulence, 95% for moderate turbulence and 150% for severe turbulence compared with today (Wikipedia, "Clear-air turbulence," captured 2026-09-23, citing Williams & Joshi 2013). That is a long-run, aggregate projection about jet-stream wind shear over decades on one heavily flown ocean crossing, not a claim about any specific flight or any specific day.

How TrackMyWings helps

TrackMyWings™ is a live flight-tracking platform in development, India-first in go-to-market with worldwide coverage. A private beta shipped on 2026-08-24: Android only, on the Play internal testing track, with a small group of named testers. The wider product, including a live map and trip management for the people waiting on someone's flight, is planned for launch rather than available today, and public launch has no fixed date. If you are trying to understand why a specific long-haul crossing tends to get bumpy, our route pages cover jet-stream-adjacent paths like Newark to Santo Domingo, and our airport pages cover the schedules of flights most likely to be crossing the same high-altitude bands, while the wider tracking build continues.

Questions people ask

Why does turbulence feel so sudden if the conditions were there for hours? Because clear-air turbulence has no visual cue. The wind-shear zone that causes it can sit in roughly the same place for hours, but a pilot flying through it has no cloud, storm or radar return to signal it in advance.

Can onboard weather radar detect clear-air turbulence? No. Aircraft weather radar detects precipitation inside clouds and storms. CAT happens in clear air with nothing for the radar beam to reflect off, so it produces no radar return at all.

At what altitude does clear-air turbulence usually happen? Most commonly between roughly 23,000 and 39,000 feet, in the high troposphere near the tropopause, where jet-stream wind shear is strongest, though the NWS defines CAT as possible at or above 15,000 feet generally.

Is clear-air turbulence caused by the jet stream? Most of the time, yes. The jet stream's edges produce sharp wind-speed changes over short distances, which is the wind shear that breaks smooth airflow into turbulent eddies.

Is turbulence becoming more frequent because of climate change? Research by Paul Williams and Manoj Joshi (2013) projects transatlantic wintertime clear-air turbulence increasing significantly under a doubled-CO2 climate scenario, with the largest projected increase in severe turbulence. That is a long-run aggregate projection, not a same-day forecast.

Sources

• Wikipedia, "Clear-air turbulence": https://en.wikipedia.org/wiki/Clear-air_turbulence, captured 2026-09-23
• Global News, "Turbulence can strike in clear skies, and aircraft radar can't detect it": https://globalnews.ca/news/5489684/turbulence-clear-skies-explained/, captured 2026-09-23
• National Weather Service (NWS ZHU training page), "Turbulence": https://www.weather.gov/source/zhu/ZHU_Training_Page/turbulence_stuff/turbulence/turbulence.htm, captured 2026-09-23
• Pilot Institute, "Clear Air Turbulence: How It Happens and How to Handle It": https://pilotinstitute.com/clear-air-turbulence/, captured 2026-09-23