High above the clouds, roughly 8 to 15 kilometres above Earth’s surface, powerful rivers of wind race across the planet at extraordinary speeds. These are jet streams – fast-flowing, narrow bands of wind in the upper troposphere that quietly govern much of the weather we experience on the ground. From steering storms across continents to triggering prolonged droughts or devastating floods, jet streams are among the most influential forces in Earth’s atmospheric system. Understanding them is key to understanding global weather patterns.
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What are jet streams?
Jet streams are narrow bands of strong wind that generally blow from west to east across the globe, sitting at altitudes of about 8 to 15 km (5 to 9 miles) – roughly the same altitude where commercial aircraft cruise. They form at the boundary between air masses with large temperature contrasts. When warm tropical air meets cold polar air, the resulting pressure difference – combined with the Coriolis effect from Earth’s rotation – drives these high-speed currents in the upper troposphere.
Their speeds typically range from 129 to 225 km/h, but can exceed 443 km/h, especially during winter when temperature contrasts between tropical and polar air are at their greatest. Jet streams are not fixed, straight corridors of wind. As NOAA explains, they meander around the globe, dipping and rising in altitude and latitude, splitting at times, forming eddies, and even disappearing to reappear elsewhere.
Jet streams also shift with the seasons. In spring and summer, as the Sun’s elevation increases, the jet stream moves poleward. By summer in the Northern Hemisphere, the polar jet stream is typically found near the US-Canada border. As autumn arrives, it migrates back toward lower latitudes. This seasonal migration directly influences the weather experienced across temperate regions.
Types of jet streams
Earth has four primary jet streams – two in each hemisphere. They fall into two main categories: polar jet streams and subtropical jet streams.
Polar jet streams
The polar jet streams are the stronger and more meteorologically significant of the two types. They form near the boundary between the polar and Ferrel atmospheric circulation cells, typically at the edge of the subtropical high-pressure zones, around 50°-60° latitude in both hemispheres. Because they sit at a lower altitude and frequently intrude into mid-latitudes, they have a direct and powerful effect on weather over North America, Europe, and large parts of Asia.
In the Northern Hemisphere, the polar jet acts as a boundary between cold Arctic air to the north and warmer tropical air to the south. The UK Met Office describes it as a high-altitude conveyor belt that influences the movement and development of weather systems, including areas of high and low pressure. When the jet flows in a straight, fast path, weather systems move quickly and conditions remain relatively stable. When it slows and buckles into large north-south waves, weather systems stall and extremes set in.
Subtropical jet streams
The subtropical jet streams form near the upper boundary of the Hadley circulation cell, around 30° latitude in both hemispheres. They are typically found at slightly higher altitudes than the polar jets and are generally weaker, though they still play a role in steering weather in the subtropics and the lower mid-latitudes. A notable example is the easterly jet stream that forms over the Indian Ocean during the Northern Hemisphere summer – it is associated with the heating of the Asian continent and is believed to help drive summer monsoon rainfall across the Indian subcontinent.
The two jet streams in the Northern Hemisphere sometimes interact. According to the Arctic Council, when the polar and subtropical jets merge or layer on top of each other, the result can be especially powerful storm systems – because the subtropical jet brings tropical heat and moisture into direct contact with cold Arctic air.
Jet streams and surface weather
The relationship between jet streams and surface weather operates through several interconnected mechanisms. Most significantly, jet streams steer mid-latitude weather systems – the temperate cyclones and anticyclones that determine day-to-day conditions across much of the world.
Steering storms and cyclones
Temperate cyclones – the large low-pressure systems that bring rain, cloud, and wind to the mid-latitudes – tend to form and travel along the path of the jet stream. NOAA’s Climate.gov identifies three key ways jet streams influence surface weather: they steer mid-latitude weather systems, they extend weaker winds all the way down to the surface (the westerly winds many of us experience daily), and they act as a sharp boundary between contrasting air masses that controls ground-level temperatures.
Storms tend to follow the edge of the jet stream, where differences between cool and warm air create turbulent conditions. The farther south the jet stream is pushed, the warmer and wetter the air becomes where it meets colder Arctic air – conditions that favour more intense thunderstorms and, in the United States, an increased risk of tornadoes.
Prolonged weather extremes: floods, droughts, and heat waves
When the jet stream is flowing strongly in a relatively straight pattern, weather systems move across regions quickly, preventing any single type of weather from dominating for too long. But when the jet stream develops large waves – known as Rossby waves – and those waves slow down or become stationary, the consequences can be severe.
A persistent ridge in the jet stream can deflect storm systems away from a region, causing weeks of dry weather and eventually drought. A stationary trough, by contrast, channels moist air repeatedly over the same area, leading to prolonged and intense rainfall and flooding. Heat waves are often linked to blocked jet stream patterns that trap warm air under a stagnant high-pressure system. Cold snaps occur when a deep dip in the polar jet sends Arctic air far south into temperate regions.
A well-documented example: in 2007 and 2012, Britain experienced severe flooding as a result of the polar jet stream remaining unusually far south through the summer months, continuously steering rain-bearing systems over the UK rather than allowing them to push further north.
Jet streams and climate change
The behaviour of jet streams is increasingly affected by climate change. The Arctic is warming significantly faster than the rest of the world, which is reducing the temperature contrast between the poles and the tropics – the very contrast that drives jet stream speed. As the Arctic Council reports, as these winds slow down, the jet stream’s waves typically grow bigger and extend farther north and south, and these larger waves move eastward more slowly. The result is more persistent and extreme weather – heat waves, floods, cold spells, and droughts that linger far longer than normal.
Research published in Nature Climate Change adds another dimension: while average jet stream speeds may shift, the fastest jet stream winds are accelerating roughly 2.5 times faster than average winds under climate change conditions, with implications for severe storm frequency and aviation. A University of Georgia study published in Nature Communications further links increased waviness of the jet stream to declining snow cover and amplified Arctic warming, showing that blocked, stalled weather patterns are already becoming more frequent – contributing to exceptional ice melt, prolonged heatwaves, and extended storm events.
Why jet streams matter for weather forecasting
Meteorologists rely heavily on jet stream data for forecasting. The position and shape of the jet stream on any given day tells forecasters where storms are likely to track, which regions face elevated risks of flooding or drought, and how long a particular weather pattern is likely to persist. Weather satellites, including NOAA’s GOES-R series, detect water vapour in the upper atmosphere to track jet stream location in near-real time, providing the foundation for modern weather prediction.
Beyond forecasting, jet streams have practical implications for aviation. Flying with the jet stream cuts flight times and reduces fuel consumption; flying against it does the opposite. The jet stream first gained widespread public attention during World War II, when American bombers over Japan encountered unexpected headwinds powerful enough to ground their missions – an early, costly lesson in the real-world consequences of ignoring these high-altitude winds.
What do you think? As climate change continues to alter the temperature gradient between the Arctic and the tropics, how might increasingly erratic jet stream behaviour reshape seasonal weather patterns in your region over the coming decades? And given how directly jet streams influence events like floods and droughts, should jet stream forecasting play a larger role in long-term climate adaptation planning?
References
- https://scijinks.gov/jet-stream/
- https://education.nationalgeographic.org/resource/jet-stream/
- https://www.noaa.gov/jetstream/global/jet-stream
- https://www.climate.gov/news-features/blogs/enso/what-jet-stream
- https://www.metoffice.gov.uk/blog/2025/what-is-the-jet-stream-and-how-does-it-affect-our-weather
- https://www.cordulus.com/glossary/jet-stream
- https://arctic-council.org/news/shifting-winds-how-a-wavier-polar-jet-stream-causes-extreme-weather-events/
- https://en.wikipedia.org/wiki/Jet_stream
- https://www.nature.com/articles/s41558-023-01884-1
- https://franklin.uga.edu/news/stories/2023/uga-research-links-climate-change-lazier-jet-stream-leading-weather-extremes
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