The best time to fly to avoid turbulence

Key facts

• "Most thunderstorms occur in the late afternoon," according to NOAA's National Severe Storms Laboratory, and thunderstorms in winter are rare because the air is more stable. [1]
• Over the southeastern US, rain peaks in the late afternoon and early evening; over the Great Plains, storms often arrive late at night; over the open ocean, rain peaks later in the morning. [2]
• Storm-related (convective) turbulence was present in 57.7% of turbulence-related US airline accidents from 2009 to 2018, and those accidents clustered in the Northern Hemisphere summer. [3]
• Jet streams are strongest in winter in both hemispheres, and National Weather Service training material lists clear-air turbulence as most frequent in winter and least frequent in summer. [4][5]
• At an average point over the North Atlantic near 39,000 feet, a 2023 study estimated about 30.6 hours of moderate-or-greater clear-air turbulence in winter 2020, against 18.6 hours in spring. [6]
• Mountain waves need winds of at least 25 knots across a ridge, so in a National Weather Service study of the southern Rockies they were most common in the cold months. [7]

Time of day: why mornings are usually calmer

The sun is the engine behind most daytime bumps. As it warms the ground unevenly, columns of warm air (thermals) rise from pavement and bare ground while cooler air sinks over water and fields. The National Weather Service notes that this thermal turbulence is a feature of warm summer days, and that many pilots prefer to fly in the early morning or in the evening, when it is weaker. [5]

Thermals mostly live in the lower part of the sky, which is why you feel them during climb and descent. The same training page notes that this kind of turbulence can ordinarily be avoided by flying higher, and airliners cruise far above it. [5] You can read more about the different sources of bumps in what causes turbulence.

Afternoon heating also powers thunderstorms, a big reason the late afternoon tends to be the bumpiest part of the day over land. [1] Crews plan to steer around thunderstorms rather than through them, and the National Weather Service advises that turbulence can extend up to 20 miles from a severe thunderstorm, which is why detours can be wide. [5]

Where the morning rule bends

• The Great Plains. In summer, storms there often march east overnight, bringing rain late at night and in the early morning. [2]
• Over the ocean. Rain over coastal waters tends to peak around midnight, and over the open ocean later in the morning, so a morning departure is not automatically calmer on tropical and ocean routes. [2]
• At cruise height. Clear-air turbulence at high altitude is tied to the jet stream rather than to sunshine. [5] On a long-haul flight, where the jet stream sits that day matters more than when you take off.

Season: storms in summer, jet streams in winter

Each season trades one kind of bump for another.

Summer is thunderstorm season over most land in the Northern Hemisphere. In the National Transportation Safety Board's review of US airline turbulence accidents, those involving storm turbulence were more common in the summer months, when there are more thunderstorms. [3] The polar jet stream also moves north in summer, typically sitting near the US-Canada border. [4]

Winter is jet stream season. Jet streams are strongest in winter because the temperature contrast between cold and warm air is greatest then. [4] That makes clear-air turbulence at cruise more frequent [5], and the stronger winds also feed mountain waves over ridges such as the Rockies. [7] On the other hand, winter thunderstorms are rare. [1]

Spring and autumn sit in between. Over the North Atlantic, a 2023 study in Geophysical Research Letters found more clear-air turbulence in autumn and winter than in spring and summer, because of the seasonal cycle in jet stream strength. [6]

These are model estimates for an average point in the North Atlantic, not counts from real flights. [6] Put in perspective, the study puts the yearly chance of moderate-or-greater clear-air turbulence at that height at nearly 1.1%: at any given moment and place, the air there was calmer than moderate about 99% of the time. [6] If you are flying one of the routes known for rougher air, our guide to the most turbulent routes explains where and why.

Is turbulence getting worse?

Gradually, over decades. The same 2023 study found that severe clear-air turbulence at an average North Atlantic point rose from 17.7 hours in 1979 to 27.4 hours in 2020, an increase of 55%. [6] The researchers saw the largest increases over the USA and the North Atlantic. [6]

That sounds alarming, but at that average point 27.4 hours is still well under 1% of the 8,784 hours in that year. What protects you most is simple: in the National Transportation Safety Board's review, only 1 of the 123 people seriously injured in US airline turbulence accidents from 2009 to 2018 was documented as wearing a seat belt. [3] For more on why bumps are uncomfortable rather than dangerous for a belted passenger, see is turbulence dangerous?

How to pick a smoother flight

1. On warm days over land, choose a morning departure when you have the choice. It avoids the afternoon peak of thermals and thunderstorms. [1][5]
2. In winter, think jet stream, not clock. Time of day matters less at cruise, so check the forecast for your route instead.
3. Flying to or near mountains? Expect some bumps on the way down at any hour. Mountain waves depend on wind, not sunshine. [7] For one example, see why flights to Denver are bumpy.
4. Check a turbulence forecast a day or two ahead, then again close to departure. A turbulence forecast for your exact route and time beats any rule of thumb, but it is a likelihood, never a promise.
5. Pick a seat over the wing if you can. Our guide to the best seat for turbulence explains why.
6. Keep your seat belt fastened whenever you are seated, and always follow your crew. [3]

How Sorapuff helps

Sorapuff's route turbulence forecast looks at your actual route and departure time instead of a rule of thumb. It reads NOAA's free GFS weather model, storm warnings (SIGMETs) and recent pilot reports, then shows a minute-by-minute timeline of smooth, light or moderate air. It's a likelihood, never a promise. The free version includes one forecast; Sorapuff Pro ($14.99 once) forecasts every flight up to three days ahead.

FAQ

Is it better to fly in the morning or evening to avoid turbulence?

Morning is usually better over land. The ground is still cool, so thermals are weak and thunderstorms have not formed yet. Late afternoon and early evening is the peak time for thunderstorms in many regions. After dark, daytime heating fades and the air often settles, but there are exceptions, such as overnight storms on the Great Plains in summer. Over oceans the daily pattern differs: rain there tends to peak overnight or in the morning.

What time of year has the least turbulence?

No season is bump-free; each trades one kind of turbulence for another. Over land, winter has the fewest thunderstorms but the strongest jet streams and more mountain waves. Summer has weaker jet streams but many more afternoon storms. Over the North Atlantic, a 2023 study estimated the fewest hours of moderate clear-air turbulence in spring and summer and the most in winter.

Is turbulence worse in winter or summer?

It depends on the kind. Clear-air turbulence near the jet stream is most frequent in winter, when jet streams are strongest, so ocean crossings and high-altitude cruise tend to be bumpier then. Storm turbulence is a summer pattern over land, especially in the afternoon. Mountain waves also favor the windy cold months. Your route decides which one matters most.

Are night flights less turbulent?

Often, over land. Without the sun heating the ground, thermals fade and the late-afternoon peak of storms has passed. But night is not a guarantee: on the US Great Plains, summer storms often arrive late at night, rain over coastal waters tends to peak around midnight, and clear-air turbulence near the jet stream can happen at any hour.

Does turbulence get worse in the afternoon?

Near the ground, yes. As the day warms, thermals make climb and descent bumpier, and thunderstorms over land are most common in the late afternoon. At cruise height, far above the thermals, the afternoon effect is much smaller, and clear-air turbulence there follows the jet stream instead. A morning departure mostly helps the climb out and, on shorter flights, the descent too.

Sources

1. Severe Weather 101: Thunderstorm FAQ, NOAA National Severe Storms Laboratory
2. Precipitation Climatology, NASA Global Precipitation Measurement Mission
3. Preventing Turbulence-Related Injuries in Air Carrier Operations Conducted Under Title 14 Code of Federal Regulations Part 121, NTSB/SS-21/01 (2021), National Transportation Safety Board
4. The Jet Stream, NOAA JetStream (National Weather Service)
5. Turbulence (aviation weather training page), National Weather Service
6. Evidence for Large Increases in Clear-Air Turbulence Over the Past Four Decades, Geophysical Research Letters (2023)
7. Mountain Wave Activity Over the Southern Rockies (2005), National Weather Service Albuquerque Center Weather Service Unit