Do changing seasons affect the jet stream?
11 Sep 2026 12:25 PM
As the UK moves from summer to autumn, the weather can change markedly.
Autumn and winter often bring more frequent spells of rain and strong winds, while spring and summer can see longer settled periods, warmer temperatures and slower-moving weather patterns.
One of the key influences behind these shifts is the jet stream: a ribbon of fast-moving air high above the Earth’s surface that helps steer weather systems across the North Atlantic.
What is the jet stream?
The jet stream is a core of strong winds around 5 to 7 miles above the surface, generally blowing from west to east. It forms close to the boundary between colder polar air to the north and warmer tropical air to the south. Because the UK sits close to this boundary for much of the year, relatively small changes in the jet stream’s position or strength can have a noticeable effect on our day-to-day weather.
When the jet stream is strong and aimed towards the UK, it can act like a conveyor belt for Atlantic weather systems. Areas of low pressure can move in quickly, bringing rain, showers and strong winds. At times, the jet stream can also help deepen low pressure systems by drawing air out from the top of the system, allowing pressure to fall and winds to strengthen.
Do changing seasons also change the jet stream?
Yes, changing seasons do affect the jet stream. The main reason is the changing temperature difference between the equator and the poles. In winter, the polar regions receive much less solar energy and cool rapidly, while the tropics remain comparatively warm. This increases the north-south temperature contrast across the hemisphere.
That stronger contrast helps strengthen the westerly winds high in the atmosphere, making the jet stream faster and often more active. For the UK, this means that when the jet stream is close to or across the country, there is an increased chance of unsettled, wet and windy weather moving in from the Atlantic.
READ MORE: What does the latest long-range forecast tell us and what role could El Niño play this autumn?
What happens in summer?
In summer, the contrast between the equator and the pole is usually smaller. The Arctic receives far more daylight, temperatures rise, and the difference between polar and tropical air is reduced. As a result, the jet stream is often weaker and can shift further north of the UK.
When this happens, high pressure has a better chance of building across or near the UK. This can bring drier, calmer and warmer conditions, particularly across southern areas. However, this is not guaranteed. A southerly displaced or unusually active summer jet stream can still bring spells of rain, showers and cooler conditions, even during the warmer months.
Why autumn and spring can be changeable
The transition seasons, autumn and spring, can be particularly changeable because the atmosphere is adjusting between its summer and winter states. In autumn, polar regions begin to cool more quickly, gradually increasing the temperature contrast that helps power the jet stream. This can lead to a more mobile Atlantic pattern, with low pressure systems becoming more frequent and sometimes more intense as the season progresses.
In spring, the opposite process takes place. The polar regions warm, the temperature contrast gradually weakens, and the jet stream can become less consistently strong. However, spring can still bring sharp contrasts, with colder air lingering to the north while warmer air develops further south. This can keep the jet stream active at times and allow rapid switches between mild, unsettled spells and colder, drier interludes.
Other factors also play a role
Although the seasons provide an important background influence, they are not the only factor affecting the jet stream. The North Atlantic Oscillation, or NAO, is one of the main patterns of atmospheric variability across the North Atlantic. In a positive NAO phase, the pressure difference between the Icelandic low and Azores high is enhanced, strengthening the westerly flow and often directing milder, wetter and windier weather towards the UK.
In a negative NAO phase, this pressure gradient weakens or reverses. The usual westerly flow can weaken, allowing weather to arrive from the north or east instead. In winter, that can increase the chance of colder, drier and sometimes snowy conditions. The polar vortex, tropical rainfall patterns and changes in Arctic sea ice can all influence these broader circulation patterns, sometimes reinforcing or counteracting the seasonal signal.
READ MORE: September weather extremes: From late-summer heat to early frost
What it means for UK weather
The position of the jet stream is crucial. If it lies to the north of the UK, high pressure may become more influential, bringing drier and more settled weather. If it runs across or close to the UK, Atlantic low-pressure systems can move in more readily, bringing spells of rain and wind. If it shifts further south, colder air can sometimes move in from the north or east, especially during winter.
A straighter, stronger jet stream tends to move weather systems through quickly, bringing changeable conditions. A more buckled jet stream can slow weather patterns down, allowing low pressure or high pressure to linger. This is why the same broad seasonal setup can still produce very different weather from one week to the next.
Can we forecast these changes?
Forecasters monitor the jet stream closely because it is such an important driver of UK weather. Its strength, position and shape are assessed alongside pressure patterns, sea surface temperatures, tropical influences and stratospheric conditions. These factors help forecasters understand whether the coming days and weeks are more likely to be unsettled, settled, mild, cold, wet or dry.
However, the atmosphere is complex. Seasonal changes can tilt the odds towards certain patterns, but they do not determine the weather on their own. The jet stream can strengthen, weaken, shift or buckle over short timescales, which is one reason why UK weather can vary so much, even within the same season.
A seasonal influence, not a fixed rule
Changing seasons do affect the jet stream, mainly by altering the temperature contrast between the equator and the poles. But the jet stream is also shaped by wider atmospheric and oceanic influences, from the NAO and polar vortex to tropical rainfall and Arctic conditions. The result is a constantly evolving feature of the atmosphere, one that helps explain why the UK’s weather can change so quickly, and why the shift from one season to the next is often anything but straightforward.
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