How do pilots know during a flight when there is turbulence coming? They turn on the fasten seat belt sign, and then it gets bumpy. The turbulence ends, and then they turn off the fasten seat belt sign.

It’s generally from pilot reports “Pirep” from aircraft that have already transited the turbulence region. You can hear them on the appropriate ATC center frequency and ATC will also inform pilots as they are approaching turbulence. The FAA encourages pilots to give Pireps for anything of interest to other pilots – good or bad.

I’m an airline pilot in the US. There are several ways we can anticipate turbulence, but nothing is certain and unexpected turbulence happens all the time.

• PIREPs, or pilot reports. Pilots tell ATC when they encounter turbulence and ATC relays the information to aircraft behind them. They are also published online and we can see them on a map on our iPads

• SIGMETs, or significant meteorological information. These are charted areas where severe turbulence or other hazards are expected.

• Turbulence forecasts on the flight release paperwork

• Turbulence forecasts on various forecasting apps installed on our EFB (electronic flight bag – literally just an iPad)

Additionally, any of the following are clear indications that turbulence in that area is likely:

• Towering cumulus clouds or thunderstorms

• Standing lenticular clouds

• Rotor clouds

• Mountainous terrain

• High winds

However, on a clear weather day, we generally play it by ear. The seat belt sign will stay on after takeoff unless the air is smooth. If it does seem smooth, we will ask ATC how the rides are ahead. If they tell us it will be smooth, we will turn the seatbelt sign off until we hit turbulence again or if we encounter any signs of possible turbulence ahead.

In addition to PIREPs (PIlot REPorts), large aircraft have weather radar devices on board, some of which are capable of detecting turbulence. Similar to PIREPs, the National Weather Service issues AIRMETs and SIGMETs which are warnings about turbulence, icing, and other conditions.

A few years back i was able to hear from the then-CEO of The Weather Channel.

One of their not-obvious larger revenue streams was weather for aircraft including turbulence. They would take their data models used for other purposes and report on sky conditions. Contracts with various carriers (Delta and others) gave them real-time updates. This enhanced their models and reports for turbulence and also for ground weather.

Why do airlines care? Turbulence costs money in terms of fuel, apparently.

Flying over any kind of storm, or weather front (change in pressure and or temperature) will probably result in rough air, and pilots are constantly checking weather. Almost all modern large aircraft have a weather radar under the nose cone (which is made of fiberglass versus carbon fiber or metal as anything conductive would interfere with radar)

I won’t get into the PIREPs that the others mentioned, but I can tell you that modern avionics have the ability to pick up weather information in flight beyond their radar scope. XM (the satellite radio company) is the largest supplier of aviation weather info in the world. There are other services that also provide this information, some which are free (ADS-B weather in the U.S.) and can be bidirectional. In other words, for larger planes, they are often reporting data as they fly, to update other planes in transit. This data can be in the form of text reports, or radar images.

The final way a pilot could learn would be by calling a ground station for a weather update, but this rarely done now, since that info is essentially available to a pilot all the time anyway.