What Causes Turbulence? A simple guide to understanding why flights get bumpy

CBS News reported that a Delta flight from Salt Lake City to Amsterdam made an emergency landing at Minneapolis–St. Paul International Airport on Wednesday evening, after severe turbulence injured several passengers.

The Airbus A330-900, carrying 275 passengers and 13 crew members, hit intense turbulence about 45 minutes into the flight while flying over Wyoming. The plane diverted to Minneapolis–St. Paul and landed safely around 7:45 p.m.

Emergency crews treated passengers at the gate, and 25 were taken to local hospitals. One passenger said there were three turbulent drops, including one of more than 1,000 feet.

The Federal Aviation Administration is investigating, and Delta says its Care Team is helping affected travelers.

FULL STORY: 25 passengers hospitalized after turbulence diverts Delta flight to Minneapolis

So What Is Turbulence?

Not all turbulence is the same. Most turbulence we experience on planes is usually just a little bumpy and not significant. But turbulence comes in different levels that can cause more serious issues.

The National Weather Service (NWS) defines turbulence as “irregular motion of an aircraft in flight, especially when characterized by rapid up and down motion, caused by a rapid variation of atmospheric wind velocities.”

The NWS Aviation Weather Center breaks turbulence into these intensity levels used in aviation:

1. Light: slight, erratic changes in altitude or attitude
2. Moderate: noticeable, but the aircraft remains under control
3. Severe: large, abrupt changes in altitude or attitude; the aircraft may temporarily lose control
4. Extreme: violent motion; control may become nearly impossible, and structural damage is possible

The turbulence this Delta flight experienced was severe enough to cause injuries and send 25 passengers to the hospital.

What Causes Turbulence?

Several variables cause turbulence:

Wind Shear

This happens when wind speed or direction changes suddenly at different levels in the atmosphere. It’s common near active weather systems like cold fronts, storms, or strong disturbances moving across the sky.

Thermal Turbulence

Warm air rises and cool air sinks. On warm days, rising pockets of hot air, called thermals, can make flying bumpy. If you’ve flown over the Rockies, you’ve probably experienced thermal turbulence.

It's not just over the mountains, but this type of turbulence is possible when the uneven heating of the Earth’s surface affects the atmosphere.

Mechanical Turbulence

When wind flows over obstacles like mountains, buildings, or forests, it becomes chaotic. This creates turbulence, especially at lower altitudes. It’s similar to how strong winds moving through tall buildings or skyscrapers in cities can cause gusty, unpredictable airflow.

Mechanical turbulence is often caused by orographic lifting, which happens when wind is forced to rise over mountains or terrain. This disrupts the airflow, creating chaotic winds and eddies that lead to turbulence, especially on the downwind side of the terrain.

Convective Turbulence

Thunderstorms and tall clouds create strong vertical air currents. These updrafts and downdrafts can cause significant turbulence. Pilots avoid these areas, but sometimes planes still encounter convective turbulence near storms.

Clear Air Turbulence (CAT)

This happens in clear skies, usually near jet streams and also over mountainous areas. It’s tricky because it’s invisible, and pilots or airlines may not know about pockets of CAT until they hit them. Once detected, information is sent to air traffic officials to warn other flights in the area.

How Do the FAA and National Weather Service Warn Pilots About Turbulence?

The FAA and the National Weather Service provide several products to keep pilots informed about turbulence:

Pilot Reports (PIREPs) give real-time updates from pilots who experience turbulence. Graphical Turbulence Guidance (GTG) uses weather data to predict where turbulence might occur and how strong it could be.

SIGMETs and AIRMETs are official weather advisories that warn pilots about significant or moderate turbulence and other hazards. Turbulence forecast charts show areas where rough air is expected, and onboard weather radar helps pilots detect convective turbulence by showing storm activity.

All these tools work together to help pilots anticipate turbulence and avoid it whenever possible, keeping flights safer and smoother.

Planes are designed to handle turbulence. It’s rarely dangerous but can cause anxiety for passengers and, of course, induce some air sickness for some folks. Most turbulence-related injuries happen when passengers aren’t wearing seatbelts. That’s why it’s always a good idea to remain buckled up.