A new powerful early-September Heat Dome is expanding across Europe. It will bring an intense late-season heatwave with surface temperatures forecast to reach the upper 30s and locally exceed 40 °C in parts of Southern Europe and the Mediterranean.
A broad warm plume surging out of North Africa is driving the pattern, with upper-air thermal anomalies climbing well above seasonal averages and setting the stage for unseasonably extreme temperatures across Spain, France, Italy, and the Balkan Peninsula.
The primary driver of this late-summer thermal surge is an expansive blocking high-pressure system parked over the Mediterranean Basin. As sinking air adiabatically compresses and warms the lower atmosphere within the heat dome, peak afternoon temperatures across low-lying valleys and coastal interiors will range from 38 °C to 42 °C across Spain, southern Spain, and Italy, with dry continental winds rapidly depleting soil moisture.
The following chart shows the mid-range forecast for Paris, France, and Zagreb, Croatia. Both indicate the heatwave will be long-lived, with temperatures significantly above the average. Predictions for next week also hint at the potential weather change with a rainy and cooler period.
This prolonged thermal ridge offers minimal nocturnal relief, as despite shorter daytime hours, overnight low temperatures refuse to drop below 22 °C to 25 °C across major urban corridors. The lack of nighttime cooling compounds physiological heat stress, elevates regional wildfire risk across dried mountain slopes, and drives high energy grid demand into early September.
The forecast model animations below represent the expansion of this upper-level ridge across Western and Central Europe, highlighting where the highest 850 hPa temperature anomalies will focus over the coming 5-7 days.
Before we dig into the details, let’s examine what a heat dome is and why it is important to understand its dynamics.
Atmospheric Dynamics: How High-Pressure Heat Domes Compress and Trap Air
When significant, record-breaking heatwaves occurred in the United States, Canada, and Europe in the past, heat domes contributed. Heat domes are usually the dominant feature of summer weather patterns on both continents.
We call this phenomenon a heat dome when extremely high temperatures develop. Here’s how it works and why understanding it on a broader scale is essential. The upper-level ridge pattern, or very warm air mass in the higher altitudes, also known as the Upper High (or blocking High), usually forms the heat dome. This weather pattern brings high, and sometimes record-breaking, temperatures to the region below.
This term is used when a broad area of high-pressure air parks over a large portion of the continent. If the event is remarkably stable and extreme, it usually lasts several days or weeks.
The heat dome works like a lid on a pot. The extensive dome traps warm air at all levels underneath, with layers sinking toward the ground. As a result, the air mass becomes anomalously warm at the lowest elevations and extremely hot near the surface.
Health and Grid Impacts: Managing Nocturnal Heat Stress and Heat Index Extremes
Excessive heat in heat domes can significantly impact human health and be dangerous to particularly vulnerable populations, such as elderly individuals, children, and those with pre-existing health conditions that can be worsened by extreme heat.
Due to prolonged exposure to high temperatures, construction workers, farmers, and other long-hour outdoor workers are at increased risk of heat-related illnesses. People living in poverty are also more susceptible to the fatalities of heat domes, as their houses are often built with heat-trapping surfaces such as concrete and asbestos.
Heat exhaustion occurs with prolonged exposure to high temperatures. It leads to dehydration and dizziness, and in more severe cases, it can progress to heat stroke.
High relative humidity during a heatwave can also significantly affect the body. For this reason, we use the Heat Index to represent the perceived feel of scorching-hot temperatures and high humidity. It illustrates the natural relationship between temperature and humidity.
When the air mass has a temperature around +35 °C, humidity below 60 percent is much less challenging than when humidity is very high, e.g., above 80%. Thus, the actual feel temperature would be near 50 degrees Celsius. Heat waves have also been associated with increased rates of heart attacks, strokes, and respiratory illnesses.
Our additional article, Health risks during a heatwave and sweltering hot weather, provides further details on the health risks.
Beneath these staggering meteorological statistics lies an even more grim threat. The danger is magnified by suffocating so-called ‘tropical nights’ where temperatures don’t drop below 24 °C, denying the human body its vital window to cool down.
Synoptic Setup: New Heat Dome Builds Across Europe through Early September
The general weather picture over the European continent this week indicates that a strong upper-level ridge is gradually expanding into western and central Europe, with two deep lows over the North Atlantic and Northern Europe. Over the weekend, the ridge expands further north and east.
A major Heat Dome will develop and dominate the continent through mid-next week.
The warmest air mass is trapped underneath the core of the heat dome aloft, spread across western and southwestern Europe until Friday and Saturday. The most anomalous temperatures will be over Spain, Portugal and France.
The deep wave over the North Atlantic will keep temperatures lower over the British Isles but will gradually weaken over the weekend as the ridge expands.
By the end of the following weekend and early next week, the upper-level ridge expands further north and east, dominating most of continental Europe.
The low over the Atlantic remains; it gets pushed westward as the ridge strengthens.
A stable and dry air mass will expand over the continent. The heatwave will cover Spain, France, Italy, and the Balkans, as well as parts of Central Europe.
This will be unusually intense for early September, resulting in significantly higher temperatures than normal over Italy, the central Balkans, and France.
As the heat dome gradually strengthens, the surface heatwave will bring the highest temperatures from Spain and Portugal into southern and central France, most of Italy, and the Balkan countries until mid next week.
The 2m temperatures will be around 10 to 14 °C above the long-term thermals for early September.
Once the ridge shifts further east mid next week, a maritime air mass from the Atlantic will gradually spread into western Europe and bring refreshment for many countries.
Daytime Highs: Regional Breakdown of 40°C+ Temperature Extremes
Southwestern Europe: Temperatures from 38-44 °C across south-central Spain and Portugal until Friday
The intense warm plume associated with the Mediterranean heat dome will keep temperatures extremely high across the Iberian Peninsula, gradually expanding into southwestern France.
Peak daytime highs on Thursday and Friday will be 40 to 44 °C across central and southern Spain and Portugal, with an extremely dry air mass. Across central and northeastern Spain, temperatures will climb into the upper 30s. With peaks approaching the 40 °C mark on Friday.
Temperatures will remain around the 40 °C peaks until mid next week over Iberia.
Western Europe: Southern France returns to near 40 °C in the south; hot days continue until Monday
As the heat dome expands aloft, the hotter air mass will spread across most of France again. The hottest days will be across southern and central parts of France, with the highest temperatures across the interior south and southwestern France.
Temperatures over central France will reach into the mid-30s, while northern France and the Benelux should remain in the upper 20s.
UK: Shorter period of mid to upper 20s through Sunday
Although temperatures will not be particularly hot over far western Europe, the daytime highs will push into the mid to upper 20s from Thursday until Sunday. The warmest air mass will be over south-central England and Wales.
Temperatures over Ireland and Scotland will be around the low 20s at most.
Southern Europe: Italy and central Balkans peak near 38-41 °C, part of the Balkans in the mid-30s
From Friday through Monday, the hottest air mass will remain over the Mediterranean, gradually surging north into Central Europe and the Balkan Peninsula. Temperatures will be back into the mid-to-upper 30s, with locally low 40s possible across parts of southern Italy and southern Balkan countries, challenging some early September record highs.
The hottest air mass will be over the Po Valley in northern Italy and Tuscany in central Italy, the central Balkans, and Greece.
Late next week could potentially deliver the pattern flip, with deep wave supporting severe weather and a cooler period
A significant change in the weather pattern appears to be shaping up for next week. An upper-level ridge is building in the North Atlantic, and a deep cold-air mass intrusion could deliver a major wave into western Europe that will travel further into the continent after next Wednesday.
This should gradually remove the current heat dome and deliver a much colder air mass, including severe weather and much-needed rain for many across western and central Europe.
While it is still too early to discuss further details, the general ensemble model trends suggest a significant refreshment is becoming increasingly likely once the heatwave vanishes next week. We will have further details on the pattern change in the coming days.
We will continue to monitor the evolution of the weather pattern and update the forecasts accordingly. Long-term trends suggest a pattern will become more dynamic into mid-September. Stay tuned for updates.
PivotalWeather and WXcharts provided images used in this article.
See also:
Winter 2026/2027 First Forecast: Super El Niño Drives a Major Weather Divide