Short answer: We checked 38 of the world's busiest routes from December 15, 2025 to January 15, 2026 with the turbulence index the Sorapuff app uses. Fukuoka to Tokyo Haneda spent the most cruise time in air the index marks moderate (19.4%), ahead of New York JFK to London Heathrow (15.7%) and Vancouver to Toronto (13.5%). Winter jet streams explain most of it. Even on those routes, more than 80% of the cruise was light or smooth.
Key facts
- Fukuoka to Tokyo Haneda, the world's third-busiest route in 2025 with about 11.5 million seats [1], spent 19.4% of its cruise in the moderate band of our index, the most of the 38 routes. [9]
- New York JFK to London Heathrow (15.7%) and Vancouver to Toronto (13.5%) came second and third. The same three led with every flight set to 35,000 feet, and stayed in the top five in both halves of the period. [9]
- Across all the cruise time we scored on the 38 routes, 91.7% was below the moderate band and 47.0% was smooth. [9]
- The day mattered more than the route: Fukuoka to Tokyo had 4 days out of 32 with no moderate-band air at all, and one day (December 19) with 87%. [9]
- The five calmest routes for jet-stream bumps were all in the tropics, led by Kuala Lumpur to Singapore, where the index never reached the moderate band. The index doesn't see thunderstorms, a main source of bumps there. [9][12]
- "Moderate band" is a likelihood, not a felt bump: in our check against 3,083 US pilot reports, about 4 to 6 in 10 reports in that band were moderate or worse, and the rest were lighter. [10]
- From 2009 to 2018, the NTSB counted 26 passengers seriously injured in turbulence on US airlines; 1 of them was documented as wearing a seat belt. [13]
- Moderate band (index 8 and up)
- Light (2 to 8)
- Smooth (under 2)
- 1 Fukuoka–Tokyo FUK–HND19.4%
- 2 New York–London JFK–LHR15.7%
- 3 Vancouver–Toronto YVR–YYZ13.5%
- 4 Seoul–Osaka ICN–KIX11.9%
- 5 Los Angeles–Chicago LAX–ORD11.8%
- 6 Denver–Phoenix DEN–PHX11.0%
- 7 Beijing–Shanghai PEK–SHA10.8%
- 8 New York–Los Angeles JFK–LAX10.8%
- 9 Los Angeles–San Francisco LAX–SFO10.4%
- 10 Sapporo–Tokyo CTS–HND10.0%
- 11 New York–Chicago LGA–ORD9.3%
- 12 Jeju–Seoul CJU–GMP9.1%
- 13 Guangzhou–Shanghai CAN–SHA8.9%
- 14 Seoul–Tokyo ICN–NRT8.3%
- 15 Shanghai–Shenzhen SHA–SZX7.7%
- 16 Chengdu–Beijing CTU–PEK7.4%
- 17 Guangzhou–Beijing CAN–PKX7.0%
- 18 Tokyo–Okinawa HND–OKA6.8%
- 19 Melbourne–Sydney MEL–SYD6.7%
- 20 Beijing–Shenzhen PEK–SZX6.4%
- 21 Tokyo–Taipei NRT–TPE6.0%
- 22 Cairo–Jeddah CAI–JED5.8%
- 23 Chengdu–Shenzhen CTU–SZX5.2%
- 24 Barcelona–Palma BCN–PMI4.8%
- 25 Atlanta–Orlando ATL–MCO4.8%
- 26 Cape Town–Johannesburg CPT–JNB4.7%
- 27 Jeddah–Riyadh JED–RUH4.2%
- 28 Dubai–Riyadh DXB–RUH4.0%
- 29 Atlanta–Fort Lauderdale ATL–FLL3.6%
- 30 Hong Kong–Taipei HKG–TPE3.0%
- 31 Orlando–San Juan MCO–SJU2.6%
- 32 Honolulu–Maui HNL–OGG2.5%
- 33 Mumbai–Delhi BOM–DEL2.1%
- 34 Bangkok–Hong Kong BKK–HKG1.4%
- 35 Bogotá–Medellín BOG–MDE1.2%
- 36 Hanoi–Ho Chi Minh City HAN–SGN0.6%
- 37 Jakarta–Singapore CGK–SIN0.1%
- 38 Kuala Lumpur–Singapore KUL–SIN0.0%
The 10 bumpiest busy routes
Ranked by the share of cruise time in the moderate band (index 8 and up), over 128 snapshots of the weather, four a day. "Main cause" is the label the Sorapuff app would give most of the route's bumpier stretches: jet stream when the wind there is 100 knots or more, wind shear otherwise. [9]
| Rank | Route | Busy-routes list (OAG, 2025) | Moderate band | Light or smooth | Main cause |
|---|---|---|---|---|---|
| 1 | Fukuoka–Tokyo Haneda (FUK–HND) | World #3 | 19.4% | 81% | Jet stream |
| 2 | New York JFK–London Heathrow (JFK–LHR) | International #10 | 15.7% | 84% | Wind shear |
| 3 | Vancouver–Toronto (YVR–YYZ) | North America's busiest domestic | 13.5% | 86% | Wind shear |
| 4 | Seoul Incheon–Osaka Kansai (ICN–KIX) | International #5 | 11.9% | 88% | Wind shear |
| 5 | Los Angeles–Chicago O'Hare (LAX–ORD) | US domestic | 11.8% | 88% | Wind shear |
| 6 | Denver–Phoenix (DEN–PHX) | US domestic | 11.0% | 89% | Wind shear |
| 7 | Beijing–Shanghai Hongqiao (PEK–SHA) | World #9 | 10.8% | 89% | Wind shear |
| 8 | New York JFK–Los Angeles (JFK–LAX) | US domestic #1 | 10.8% | 89% | Wind shear |
| 9 | Los Angeles–San Francisco (LAX–SFO) | US domestic #3 | 10.4% | 90% | Wind shear |
| 10 | Sapporo–Tokyo Haneda (CTS–HND) | World #2 | 10.0% | 90% | Wind shear |
Sources for the lists: OAG [1][2], with the full world and international top 10 as reported by Time Out [3] and AirlineRatings [4], and OAG's US lists [5][6]. The top three are clearly ahead: in 90% of 2,000 random resamples of the 32 days, Fukuoka to Tokyo ranked 1st to 3rd, JFK to London 1st to 4th, and Vancouver to Toronto 2nd to 8th. Ranks 4 to 20 are close enough that another winter could reorder them. [9]
The 5 smoothest busy routes (for jet-stream bumps)
| Route | Busy-routes list (OAG, 2025) | Moderate band | Smooth (under 2) |
|---|---|---|---|
| Kuala Lumpur–Singapore (KUL–SIN) | International #3 | 0.0% | 95% |
| Jakarta–Singapore (CGK–SIN) | International #6 | 0.05% | 86% |
| Hanoi–Ho Chi Minh City (HAN–SGN) | World #4 | 0.6% | 71% |
| Bogotá–Medellín (BOG–MDE) | Latin America's busiest domestic | 1.2% | 68% |
| Bangkok–Hong Kong (BKK–HKG) | International #8 | 1.4% | 70% |
These are calm for the kind of bumps the index measures, not a promise of a smooth ride: in the tropics, bumps come mostly from thunderstorms, which this index doesn't see (more below). [12]
Why these routes: the winter jet stream
Jet streams are fast rivers of wind around 30,000 feet, and they are strongest in winter. [11] Where the wind changes sharply with height and across the flow, the air gets choppy without a cloud in sight: clear-air turbulence. That is what our index measures. [8] Every route in the top 10 lies in the Northern Hemisphere's middle latitudes, under the winter jet streams of East Asia, North America and the North Atlantic. [9]
Japan and Korea: under the winter jet
Fukuoka to Tokyo runs east-northeast along southern Japan, under the winter jet stream. Across our 128 snapshots, the fastest wind along the route averaged 130 knots and reached 189 knots, and 71% of its bumpier stretches sat in wind of 100 knots or more. [9] Seoul to Osaka (4th) and Sapporo to Tokyo (10th) share the same skies. Because these flights are short, a few bumpy stretches are a big share of the trip: 19.4% of Fukuoka to Tokyo's roughly 70 minutes above 17,000 feet is about 13 minutes. [9]
Fast wind on its own isn't what makes bumps. Tokyo to Okinawa and Tokyo Narita to Taipei had even faster winds, averaging 159 and 157 knots at their peak, yet ranked 18th and 21st. What makes the air choppy is how sharply the wind changes from one height or place to the next, and inside a broad, smooth jet the ride can be calm. [8][9]
The North Atlantic and North America
Moderate clear-air turbulence is more common over the midlatitude oceans than over land, and over the North Atlantic more common in autumn and winter than in spring and summer. [14] JFK to London had some moderate-band air on all 32 days, from 1.6% of the cruise on its calmest day to 33% on its roughest (January 8). [9] Across North America, Vancouver to Toronto, Los Angeles to Chicago and New York to Los Angeles cross the continent under the same winter jet. Most of their bumpier stretches sat in wind below 100 knots, in the sharp wind changes around weather systems that the app labels "wind shear". [9]
Why the tropics look smooth, and what that hides
Near the equator, upper winds are light: along Kuala Lumpur to Singapore, the fastest wind averaged 13 knots. With little wind, there is little wind shear, so the index stays low. [9] But the tropics have their own bumps. The UK Met Office notes that parts of Southeast Asia are frequently affected by turbulence from storms, especially in storm seasons. [12] Storms don't show up in this index, and crews steer around storm cells with weather radar, forecasts and pilot reports and SIGMETs. So read the smoothest list as "smooth for jet-stream bumps".
What "moderate band" means, calmly
- It's a likelihood. In our check of the index against 3,083 US pilot reports, about 4 in 10 reports at the band's lower edge were moderate or worse, rising to about 6 in 10 at the very top of the scale. The rest were light or smooth. [10] Pilots tend to file a report when there is something to report, so the share of bumpy air is probably lower than that.
- Moderate turbulence is uncomfortable, not dangerous. It makes walking and food service difficult; the airplane stays in control throughout. Our guide to turbulence levels explains each level. Airliners are built to carry at least 2.5 times their own weight without damage. [15]
- The real risk is being unbelted. Of the 26 passengers seriously injured in US airline turbulence from 2009 to 2018, only 1 was documented wearing a seat belt [13], while US and foreign airlines carried about 1 billion passengers to, from and within the US in 2018 alone. [16] More in is turbulence dangerous?
- Real flights do better than our model. Airlines plan each day's route and altitude around the winds, and pilots climb or descend away from bumps that other crews report. Our model flies a straight great circle at one height and can't do either.
How we measured it
This is a model-based estimate, not measured bumps. We scored each route on NOAA's GFS weather model at 0.5° (about 55 km) with the Ellrod index (TI1), the clear-air turbulence index the Sorapuff app uses. It scored 0.68 against 3,083 US pilot reports, where 0.5 is a coin flip: good at telling bumpier air from smoother air, never a promise. Turbulence changes by the day and by the hour, and one winter is one winter.
- Routes: the 38 airport pairs named in OAG's 2025 busiest-routes lists (seats scheduled in 2025): the world top 10, the international top 10, China's and the USA's busiest, and the busiest domestic route of each other region. [1][2][3][4][5][6]
- Weather: GFS analyses, the model's best picture of the current weather, at 00, 06, 12 and 18 UTC every day from December 15, 2025 to January 15, 2026: 128 snapshots. As the app does, we downloaded only the wind and height fields at 200 to 400 hPa (about 24,000 to 39,000 feet) from NOAA's open data on AWS: 382 MB in all. [7]
- Flights: a great-circle path with the app's flight profile: cruise height by distance (22,000 to 37,000 feet), a point every 2 minutes, scored wherever the plane is at 17,000 feet or higher (what this page calls the cruise). Each snapshot scores the whole route on the air at that moment.
- Index: Ellrod TI1 = vertical wind shear × deformation, on the layer around the flight level, in the app's bands: smooth under 2, light 2 to 8, moderate band 8 and up. [8][10] Our analysis code reproduces the app's own calculation to four decimal places.
- Score: the share of all scored points in the moderate band, over all snapshots. Ties go to the higher mean index. Rank ranges come from 2,000 random reshuffles of the 32 days.
- Checks: with every flight at 35,000 feet instead, the top three and the five smoothest were the same. In each half of the period (December 15 to 31 and January 1 to 15), the same three were in the top five, and four of the five smoothest were in the bottom five.
What it can't tell you: bumps from thunderstorms, mountain waves, or the low-level air near airports (so short hops are judged only on their brief time above 17,000 feet); storm and turbulence warnings (SIGMETs), which the app adds for a real flight but we didn't use for past days; and what any single flight felt like. The full results for all 38 routes, with mean index, winds and rank ranges, are in the data file (CSV).
If you're flying one of these routes this winter
- Look at your day, not the ranking. On the top route, the share of moderate-band air ranged from none to most of the cruise depending on the day. A turbulence forecast for your flight tells you far more.
- Keep your seat belt fastened whenever you're seated, loosely if you like. It's the single most effective protection. [13]
- Expect a few bumpy stretches and the seat belt sign. On Fukuoka to Tokyo, about four-fifths of the cruise was light or smooth even last winter. [9]
- Sit over the wing if you can; see the best seat for turbulence. And always follow your crew.
For the yearly ranking of the most turbulent routes overall (mountain hops lead it), see the most turbulent flight routes and airports.
How Sorapuff helps
Sorapuff runs this same calculation for your own flight, on your phone: it reads NOAA's free GFS forecast along your route, adds SIGMET storm warnings and recent pilot reports, and shows a minute-by-minute timeline of smooth, light or moderate air. It's a likelihood, never a promise. In the air, the bump meter shows how small each bump really is. One forecast is free; Sorapuff Pro ($14.99 once) forecasts every flight up to three days ahead.
FAQ
What was the bumpiest busy flight route in winter 2025–26?
Of 38 of the world's busiest routes, Fukuoka to Tokyo Haneda spent the most cruise time in air our turbulence index marks moderate: 19.4%, from December 15, 2025 to January 15, 2026. New York JFK to London Heathrow (15.7%) and Vancouver to Toronto (13.5%) came next. These are model estimates from NOAA weather data, not measured bumps.
Is New York to London turbulent in winter?
It had more moderate-band air than almost any other busy route we checked: 15.7% of the cruise, on a scale where the busiest routes ranged from 0% to 19.4%. It was also steady: some on every day, and about a third of the cruise on its roughest day. Over 80% was light or smooth. Airlines plan each day's North Atlantic route around the winds, and crews avoid reported bumps.
Why is Fukuoka to Tokyo so bumpy?
The route runs along southern Japan under the winter jet stream: the fastest wind along it averaged 130 knots in our snapshots and reached 189. Wind that changes sharply with height makes clear-air turbulence. The flight is short, so a few bumpy stretches are a large share of it, about 13 of roughly 70 minutes above 17,000 feet.
Which busy flight routes are the smoothest?
For jet-stream bumps, the calmest were tropical: Kuala Lumpur to Singapore, Jakarta to Singapore, Hanoi to Ho Chi Minh City, Bogotá to Medellín and Bangkok to Hong Kong, all with 1.4% or less of the cruise in the moderate band. Upper winds there are light. Thunderstorms can still cause bumps in the tropics, and pilots steer around them.
Should I avoid the bumpiest routes?
No. These are some of the world's busiest, most routine flights, and moderate turbulence is uncomfortable rather than dangerous for a belted passenger. Even on the top route, more than 80% of the cruise was light or smooth last winter, and some days had no moderate-band air at all. Keep your seat belt fastened when seated and follow your crew.
Sources
- The busiest flight routes of 2025, OAG
- South Korea's Jeju (CJU)-Seoul Gimpo (GMP) is the World's Busiest Airline Route in 2025, OAG press release, December 22, 2025
- These were officially the world's busiest flight routes this year, Time Out, December 29, 2025
- Busiest international routes of 2025, AirlineRatings, January 27, 2026
- The USA's Busiest Airline Routes in 2025 Show Strong Domestic Demand, OAG via GlobeNewswire, December 22, 2025
- The Busiest Flight Routes of 2025 Revealed, TravelPulse
- NOAA Global Forecast System (GFS), Registry of Open Data on AWS
- Ellrod Index, SKYbrary Aviation Safety
- Sorapuff winter route study: 38 routes scored on 128 NOAA GFS 0.5° analyses (December 15, 2025 to January 15, 2026) with the app's turbulence index, Simple Products Labs (November 2026); method on this page, results in the data file
- Sorapuff forecast check: the Ellrod index from NOAA GFS forecasts scored against 3,083 US pilot reports, Simple Products Labs (November 2026); see how accurate are turbulence forecasts?
- The Jet Stream, NOAA JetStream (National Weather Service)
- Turbulent flights and the climate connection, Met Office, October 2025
- Preventing Turbulence-Related Injuries in Air Carrier Operations Conducted Under Title 14 CFR Part 121, Safety Research Report SS-21/01 (2021), NTSB
- Evidence for Large Increases in Clear-Air Turbulence Over the Past Four Decades, Geophysical Research Letters (2023)
- 14 CFR § 25.337, Limit maneuvering load factors, Legal Information Institute (Cornell Law School)
- 2018 Traffic Data for U.S Airlines and Foreign Airlines U.S. Flights, Bureau of Transportation Statistics