Europe's extraordinarily hot summer of 2026: why the same weather pattern kept returning
Western Europe's warmest summer on record was the same atmospheric pattern coming back, from May into September.
People keep describing this summer as one long heatwave. It wasn't. The same atmospheric pattern came back multiple times, which is why it felt like it would never end.
How hot was the European summer of 2026?
Western Europe fitted 4 of its 10 most severe heatwaves since 1950 into the May–August 2026 period alone. Severe means three things at once: how hot, how long, and how much of the region was affected. The June spell, lasting roughly from 18 to 28 June, comes second only to August 2003. All four heatwaves this summer were more intense than that 2003 heatwave. The UK hit 35°C on nine days, and in every summer month, which had not happened before.
Western Europe, specifically, had its warmest summer on record, 2.54°C above the 1991–2020 average. Europe as a whole was third-warmest, at 1.17°C above the average over the same time period. Those are two distinct measurements. The multiple repeats of the pattern were seen only in the west.
Over European land, that 1.17°C makes June–August 2026 the third-warmest summer in the ERA5 record. 2024 was warmer, at +1.55°C, and 2022 at +1.34°C. The summer mean in western Europe was 21.69°C. It beat 2003. 2003 is a bad comparison if you treat it as another hot one-off. In 2003 the hot summer stuck out from cooler summers around it. Every summer since 2015 has been warmer than average, and 2022 had already come close to the 2003 mark. 2026 went past it. The figures in this section are from the Copernicus summer review.
The mean hides how the season was built. Heat arrived as separate spells, several of them early.
| Spell |
Length |
Where it sits |
| 23–29 May |
7 days |
one of the ten most severe since 1950 |
| 18–28 June |
11 days |
most severe of 2026, second only to August 2003 |
| 6–12 July |
7 days |
more intense than August 2003 |
| 11–15 August |
5 days |
more intense than August 2003 |
June was a day shorter than the 12-day August 2003 heatwave.
On 24 June, 29 July and 14 August, about 75% of western Europe reached at least 30°C, and more than 30% reached 35°C. May and September still put 30°C across more than 40% of the region. In May and September 2003 that share stayed under 13%.
France makes the same point in local numbers. During the June heatwave, about 40% of France went over 40°C. Across the summer, 90% of France saw at least one day at 35°C or higher, and 45% saw 40°C.
Heat stress is the part that matters for sleep and for hospitals, and it is not the same number as the air temperature. By the end of summer, 52% of Europe had hit "very strong" heat stress on the Universal Thermal Climate Index. The old widest extent of that category was 46%, in 2010. In late June, humidity in parts of the UK and Ireland pushed the feels-like temperature about 5°C above the air temperature, and by as much as 9°C in places. August was a drier heat. Feels-like temperatures sat closer to the thermometer, often only about 2°C above it.
What is atmospheric blocking?
This atmospheric pattern has a name: atmospheric blocking. Most of the time the jet stream runs west to east, Atlantic weather arrives, and then it moves on as it is pushed eastwards by the planetary circulation. A block is an area of high pressure that stays stuck in one place, so the jet has to bend around it as it can't pass through it.
Directly under that high-pressure area the air sinks, which means the sky stays clear and the heat builds on itself. If this system remains stuck for too long, the soil starts to dry and the sunshine starts heating the air instead of evaporating water, creating that oven-air effect.
You can see it on the 500 hPa surface, the height where pressure is 500 hPa, about 5.5 km up. Meteorologists call that height Z500. Warm air takes up more room, so a warm column pushes that surface upward. The wind follows the bulge instead of cutting across it. Z500* is that field with the usual seasonal height taken off, so the bulge that should not be there is what you actually see. Red, in the maps on this site, is that extra height.
Hot air drawn up from the south adds to the sinking and the clear skies. Both happened this summer. The peaks on 24 June and 11 July had a push of subtropical air, helped at times by low pressure west of Iberia. A review of Euro-Atlantic blocking and extremes goes through this properly: Kautz et al., 2022.
What an omega block looks like
June had the picture-book version of an atmospheric block, an omega block. One high-pressure area in the middle and a low-pressure area on each side, like the Greek letter Ω. The first figure is that sketch. It is a diagram, not a map of 2026.
Omega block, a type of atmospheric blocking
CEDIM went through that heatwave day by day and found that there was an omega phase, but it did not lock in the way a classical high-latitude block does. Their report covers 13–29 June across western, central and southern Europe. They also describe a cut-off low west of Iberia that helped pull warm air north. Enough to hold a record heatwave. Not a high that sat still for months.
The odd part of the 2026 climate is that a version of this pattern kept coming back from May into September. Copernicus describes repeated blocking highs, the jet disrupted, Atlantic storms diverted, and heat building under clear skies. Copernicus Figure 16 puts every peak from May to September on one page: 500 hPa height, the wind at that level, and temperature at about 1.5 km.
A clean historical omega, if you want the shape with less arguing, is the 2015 European omega block, around 1 July 2015. That one is a reference picture. It is not 2026.
The second figure is a real day. 24 June 2026, during the June spell. The high sits over the region that was breaking temperature records that week.
ERA5T. Z500* is the 24 June 00:00 UTC geopotential height anomaly. The labels are that day's maximum 2m temperature.
The same day is on the explorer.
Why were the nights so warm?
The ocean played its part in two distinct ways.
Close to the coast, the seas hit seasonal records: the southern North Sea, the Channel, the Irish Sea, Biscay, west of Portugal, and the western Mediterranean. They heated up under the highs, which brought clear skies and light winds, and as a result held the daytime heat into the night. The blocks are why nightfall did not bring relief. They made each spell harder to get out of.
In summer 2026, 56% of the European ocean domain was much warmer than average, and 22% had record-high summer sea surface temperatures. Daily averages reached 22.6°C in Biscay on 13 August and 29.4°C in the western Mediterranean on 15 August. Parts of the western Mediterranean went over 30°C in July, August and September. Parts of Biscay were in an extreme marine heatwave in July.
Clear skies and light winds heated the sea surface and stirred it less, so cooler water stayed below. Tropical nights, meaning the night never really cooled, reached northern Germany, the Netherlands and southern Britain. Parts of northeastern Spain and Italy had 30–45 more tropical nights than average.
Further west, the subpolar North Atlantic was cold, and had been since at least December 2025, before summer started. A cold subpolar ocean next to a warm subtropical one can favour a wavier jet and a preference for high pressure over Europe. That cold patch may have helped the highs keep coming back, causing new blocks to form. However, Copernicus says the reasons the blocks kept returning are still being explored, and it is still an open question.
Drought, rivers, fires
The highs landed on a landscape that was already set up to dry out.
Much of western Europe and Italy came out of a very wet winter, through a dry spring, into serious summer soil-moisture deficits. Parts of central and eastern Europe were already dry in spring. By late summer, drought on the three-month standardised precipitation–evapotranspiration index covered a lot of western and central Europe, the Balkans and northwestern Türkiye. About 46% of European land was in drought at the end of August, and a large share of that area was extreme drought.
Rivers show how long it lasted. In the European Flood Awareness System record, which starts in 1992, summer 2026 had the most severe low-flow conditions for Europe as a whole. About 67% of the river network was below average. At their outlets, the Loire, Seine, Rhine, Glomma, Vistula and Danube all had their lowest summer-average flow in that record. These are simulated flows from EFAS, not a gauge reading at every bend.
Fires followed the fuel, not only the afternoon temperature. A wetter winter and early spring grew extra vegetation in some regions. The later drying and the repeated heatwaves turned that growth into fuel. Spain and France both had exceptional seasons. The sequence is the point: moisture, growth, then a stuck dry pattern.
Did climate change cause the 2026 European heatwaves?
Declaring one root cause is tempting, but it tends to oversimplify a complex dynamic in a large system. Two different questions get collapsed into that one, and the answers are not equally solid.
The first is whether this kind of block is becoming more common, or lasting longer. "Just weather" ignores how hot it was and why. "Just climate change" ignores that we still don't have an accurate way of projecting the future frequency of atmospheric blocking, or its likely duration.
My MSci ran into the same difficulty at the labelling and manual detection stages. The three standard definitions, on 40 years of European summers, agreed that a day had atmospheric blocking present on only 3 out of 3,680 days. Separately, three physics students and three academics checked the maps by hand, and their labels agreed with each other at least 95% of the time. The standard methods disagree, yet the people were able to stay consistent. Woollings et al., 2018 is the review I still start from, and it is cautious for a reason.
The second question is how hot a familiar setup has become. One thing that can help provide better insight into the system is the temperature profile that follows a persistent atmospheric pattern. World Weather Attribution looked at June, which has a similar southerly flow when compared to historic heatwaves. Simulate that same flow over 1976 and the days come out about 3.5°C cooler. In 2003, about 2°C cooler. The nights would have been about 2.4°C cooler than in 1976, and about 1.3°C cooler than in 2003.
Over the region they studied, the hottest daily temperatures are warming at about three times the global rate, and nighttime temperatures at about twice that rate. In large parts of western Europe, June is warming faster than the other months.
Summer 2026 was extreme because blocking-type highs kept returning from May into September. June included an omega phase, shorter-lived than a classical high-latitude block. Sunshine, dry soils, warm seas around Europe and humid nights then compounded. The reason those highs kept returning, including a possible role for the cold blob, is still open. The intensity of the heat, given that kind of flow, is not what the same kind of flow produced twenty or fifty years ago.
The atmosphere arranged itself in a way we have seen before. Yet, Western Europe had never had a summer this hot.
Explore blocking maps · Science and glossary