In this week’s Met Office Deep Dive, we unpack a weekend of dramatic weather across the UK, explore the science behind supercell thunderstorms, and look ahead to a week of changeable conditions shaped by a dynamic jet stream.
Was there a Supercell over the weekend?
So, did the UK experience a supercell thunderstorm? The answer, in fact, is yes, at least one storm bore the hallmarks of a supercell, and possibly more.
Supercells are the most organised and long-lived type of thunderstorm. They are defined by a rotating updraft, known as a mesocyclone, which allows them to sustain themselves for hours and produce severe weather including large hail, damaging winds, and even tornadoes.
While the UK rarely sees supercells, the ingredients were in place: strong wind shear, elevated instability, and a moist, warm air mass. Doppler radar showing rotation aloft, and hail reports of up to 2 cm in southeast Scotland, support the supercell diagnosis. One storm even showed potential for 4 cm hail, though this remains unverified due to its rural location and the fact that it occurred late at night.
READ MORE: What's in store for the next week: An active jet stream fuels more changeable weather
A finely balanced setup
The weekend’s weather was a case study in how delicate the balance can be between a major outbreak of severe weather and a more modest event. Forecast models had flagged the potential for significant thunderstorms, particularly across northern England and southern Scotland, but the outcome hinged on surface temperatures.
Early cloud cover and elevated convection, storms forming above a stable surface layer, limited daytime heating in some areas. While Surrey saw temperatures in the low 30s, parts of northwest England and northeast Wales remained cooler than expected, reducing the likelihood of surface-based storms.
Two scenarios were considered: one where surface temperatures rose enough to trigger deep convection and potentially tornado-producing supercells, and another where elevated storms dominated. The latter played out, but not without impact. Multiple storm cells tracked over the same areas, bringing over 40 mm of rain and some localised flooding.
Radar revelations
Radar imagery was key to diagnosing the weekend’s storms. Traditional reflectivity radar showed the precipitation structure, while Doppler radar revealed wind patterns within the storm. The presence of inbound and outbound winds in close proximity, known as a velocity couplet, confirmed rotation.
These radar signatures, combined with ground reports and photographic evidence, strongly suggest that at least two supercells occurred.
A little wind, a little rain, and a whole lot of humidity, here's how the rest of the week is shaping up 👇 pic.twitter.com/BP88ThU8Gw
— Met Office (@metoffice) June 25, 2025
The role of the jet stream
The return of the jet stream to the UK has been a major driver of recent weather patterns. Typically, stronger and more active in autumn and winter, the jet stream can still play a significant role in summer when it dips southward or becomes more amplified.
Last week, a powerful jet streak developed over North America due to a strong temperature contrast between hot, humid air over the Gulf of Mexico and cooler air over the Rockies. This amplified jet stream is now crossing the Atlantic and influencing UK weather.
As it arrives, it’s bringing a conveyor belt of low-pressure systems and frontal boundaries, leading to a more unsettled spell. The position of the jet stream is also crucial in determining where the boundary lies between cooler air to the north and hot, humid air to the south.
Looking ahead: Thunderstorm risk and heat on the horizon
The forecast for the coming days remains finely balanced. A filament of the jet stream currently over Iberia is expected to move northeast into France, bringing with it the potential for severe thunderstorms. These storms are likely to remain over the near continent, but there is a risk they could brush the far southeast of England.
Forecast CAPE (Convective Available Potential Energy) values are high over the continent, indicating a lot of energy available for storm development. Combined with wind shear and rising air, this creates a favourable environment for large hail, frequent lightning, and torrential rain.
Elsewhere in the UK, showers are expected to drift north across the southeastern half of the country, while the northwest remains wetter due to frontal systems driven by the jet stream. Rainfall totals could exceed 50 mm in parts of Cumbria and western Scotland by Friday.
READ MORE: What role does convection play in weather?
Temperature trends: A north-south divide
Temperatures this week will reflect the contrasting air masses on either side of the jet stream. The southeast is likely to see highs in the mid-to-high 20s, with a chance of reaching 30°C early next week.
Meteorograms for London and Glasgow illustrate this contrast. London shows a wide range of possible temperatures on Tuesday, from average to well above average, before returning closer to normal midweek. Glasgow, meanwhile, sees a more modest rise, peaking in the low 20s before cooling again.
Global context: Heatwaves in Europe and the US
The UK is not alone in experiencing extreme weather. A significant heatwave is ongoing across southern and eastern Europe, with temperatures rising across the Balearics, Corsica, Sardinia, and Italy. By Friday, the heat is expected to build again across Spain and Portugal.
In the US, northeastern states are experiencing record-breaking heat. At 8am on Tuesday, temperatures had already reached 32°C at JFK and Newark airports, while New York City hit 39°C, breaking its June record. This heat is being driven by a ridge in the jet stream, drawing hot, humid air north from the Gulf of Mexico.
Temperatures are set to climb in the UK during the coming days but other parts of the globe are also currently experiencing some intense heatwaves.
— Met Office (@metoffice) June 24, 2025
Firstly eastern parts of the USA are seeing near record heat for June with New York City approaching 40 Celsius today 🥵 pic.twitter.com/gxGRKkiAU8
The weekend and beyond
As we head into the weekend, the jet stream is expected to shift northward, allowing high pressure to build from the south. This will bring drier, brighter conditions to much of the UK, particularly in the south and east. However, the northwest may remain unsettled with further rain and breezy conditions.
By Sunday and into early next week, there is potential for another warm spell in the southeast, though it is expected to be less intense and more localised than the recent heat. The probability of 30°C is highest in the southeastern quarter of the UK, with temperatures more widely in the low to mid 20s.
Longer-term outlook
Looking further ahead, the most likely scenario is for the Azores High to extend its influence across the UK, bringing mostly dry and settled weather. However, there is also a chance that the high retreats, allowing a pulse of the jet stream to bring more changeable conditions, particularly to northern areas.
Forecast confidence decreases beyond next week, as is typical for this time of year. Summer weather patterns are often more variable and less predictable due to weaker global signals. Nonetheless, the general trend suggests a return to more average conditions after the brief hot spell.
From the rare occurrence of supercells to the influence of the transatlantic jet stream, the atmosphere is in a state of dynamic flux. While the southeast may see further warmth and the occasional thunderstorm, the northwest remains under the influence of Atlantic systems.
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