Early September Heat Dome Expands Across Europe: 40°C+ Highs Target the Mediterranean and Balkans

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.