Over the past few days, many parts of the UK have experienced slow-moving summer downpours, and the pattern looks set to continue.
In this week’s Deep Dive, we explore the meteorological ingredients behind these showers and thunderstorms.
A wet start to the week
The week began with significant rainfall across parts of Northern Ireland, where an amber warning was issued from Sunday night into Monday. Killowen recorded 72mm of rain in just 24 hours, close to the average monthly total for July. Western and northwestern Scotland also saw heavy rain, leading to localised flooding and travel disruption. Elsewhere, central and eastern parts of the UK experienced scattered heavy showers.
There will be further slow-moving heavy showers and thunderstorms tomorrow, particularly across central and southern parts of England and Wales 🌩️
— Met Office (@metoffice) July 22, 2025
Some localised flooding and disruption could be possible pic.twitter.com/TiA8FTazfy
What’s driving these downpours?
To understand why these showers are so persistent and slow-moving, we need to look high into the atmosphere, specifically at the 300 hPa pressure level, which is around 30,000 feet above sea level. This level is often used to analyse the jet stream, but this week we’re focusing on temperature patterns at that altitude.
A pool of cold air is forecast to move from Iceland into Ireland and then into southwest England by Wednesday morning. When this cold air sits above relatively warm and humid surface conditions, it creates a steep temperature gradient. This enhances thermal uplift, encouraging air to rise rapidly and form shower clouds and thunderstorms.
The role of the jet stream
The jet stream is also playing a key role. It is currently dipping south of the UK, placing us on its colder side. This setup has led to the development of a cut-off upper vortex, an area of low pressure high in the atmosphere. This creates a vacuum effect, drawing surface air upwards and further enhancing the potential for storm development.
READ MORE: Why has it been so warm and humid recently?
Surface conditions add to the mix
At the surface, light winds and sea breezes are contributing to convergence zones, areas where winds from different directions meet and force air to rise. These zones are expected to form along the south coast and in East Anglia on Wednesday afternoon. Where convergence occurs, showers are likely to develop and remain stationary for extended periods.
In East Anglia, for example, surface winds from the northwest will meet upper-level winds from the southeast. This opposing flow creates wind shear, which can influence storm movement and longevity. In this case, the winds are light and largely cancel each other out, meaning storms are likely to remain slow-moving.
Dartmoor: a hotspot for development
Elevated terrain such as Dartmoor is another factor. As the sun heats the ground, the air above it warms and rises more readily than the surrounding air. This makes Dartmoor a focal point for repeated shower development throughout the day.
READ MORE: Climate change impacting the natural world
What to expect on this week
By Wednesday afternoon, clusters of heavy showers and thunderstorms are expected to align along the south coast and into East Anglia. Some areas could see 30-40mm of rain in just a few hours, while others nearby may remain dry. The Pennines and southeast Scotland are also likely to see some heavy, though more scattered, showers.
As we move into Thursday, the upper vortex shifts eastward, with the heaviest downpours lingering over East Anglia. Meanwhile, warmer air begins to move into western parts of the UK, and a ridge of high pressure starts to build.
By Friday, many areas will be drier, with the best of the sunshine in the east and southeast. Saturday looks warm and sunny for much of England and Wales, though showers will continue in Scotland and Northern Ireland.
There is some uncertainty for Sunday, with models differing on the track of an approaching low. Into next week, a more settled pattern may emerge, particularly for England and Wales, as higher pressure builds from the southwest.
Keep up to date with weather warnings, and you can find the latest forecast on our website, on YouTube, by following us on X and Facebook, as well as on our mobile app which is available for iPhone from the App store and for Android from the Google Play store.