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An extended heat wave has impacted large parts of Europe for the second decade of August 2025. A complex ridge pattern allowed very hot air masses to reach the Continent. Many measuring sites in Southern Spain recorded maximum temperatures of more than 45 °C on multiple occasions. Atop of the Brocken Mountain, a new record for the monthly maximum temperature of 29.5 °C was observed.
By early August 2025, little was hinting at an intense heat wave across Central Europe. The synoptic pattern over Europe was dominated by a strong trough over the North Sea. At times, the synoptic pattern exhibited an unusually strong westerly flow for the midst of summer. This general flow pattern over Europe was distributed by the extratropical transition of tropical cyclone DEXTER at the end of the first decade of August 2025. With this extratropical transition, a broad trough over the Eastern North Atlantic formed. This amplified the westerly flow pattern over Europe. A large ridge could expand northwards across the Continent. Additionally, a cut-off low over the Central Mediterranean exacerbated the geopotential gradients across Europe.
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11-day mean 500 hPa geopotential (left), 500 hPa geopotential anomaly (middle), and 850 hPa temperature anomaly (right), 09.08.2025 - 19.08.2025, source:
PSL NOAA
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The geopotential anomaly for the period of the heat wave reveals a strong positive geopotential anomaly stretching across Europe. Minor signals of the cut-off located over the Central Mediterranean can also be seen in the geopotential anomaly field. The 850 hPa temperature anomaly field also shows a strong positive 850 hPa temperature anomaly across much of Western and Central Europe. Temperature deviations of up to 10 K are derived for the respective period across Southern France. A detailed analysis of the daily development of the synoptic pattern across Europe shows that by August 07, 2025, hot air masses could penetrate northwards across the Continent. By August 09, 2025, the advection of hot air masses to Southern Europe increased due to ex-tropical cyclone DEXTER, which reached the Eastern North Atlantic.
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Daily development of the 500 hPa geopotential, 1000 hPa to 500 hPa thickness, and sea-surface pressure over Europe, 09.08.2025 12 UTC - 20.08.2025 12 UTC, source:
wetter3.de
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At the same time, a trough over Northern Europe led to an intermediate decrease in the temperatures across Central Europe. By August 12, 2025, the trough over Northern Europe has moved over Western Russia. This allowed the ridge to once again expand northwards across Europe. With this, very hot air masses could again advance across Central Europe. 850 hPa temperatures of more than 20 °C were observed over Central Europe. In Southern Europe, the 850 hPa temperature reached up to 30 °C. By August 15, 2025, the amplification of the ridge decreased again. Another trough over Western Russia impacted the weather across Central Europe. Much cooler air masses related to the trough reached the area. In the northern parts of Germany, the temperatures reached only slightly above the 20 °C mark.
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Daily development of the 850 hPa temperature over Europe, 09.08.2025 12 UTC - 20.08.2025 12 UTC, source:
wetter3.de
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Over the Eastern North Atlantic, another trough formed. With the trough, again, very hot air masses reached the Iberian Peninsula by August 16, 2025. 850 hPa temperature shot up to values close to 30 °C. By August 20, 2025, another trough reached Western Europe. With the trough, much cooler air masses arrived in Western Europe, which also terminated the heat wave in these areas. This trough also brought heavy precipitation to the Alps as it moved eastwards across Europe.
The largest impacts of this heat wave were reported from the Iberian Peninsula and Southern France. From August 02 through to August 18, 2025, at least one measuring site in Spain recorded a daily maximum of more than 40 °C. In Southern France, maximum temperaturesabovef 40 °C were observed from August 09 through to August 17, 2025. Two peaks with maximum temperatures of up to 45 °C were reported across the Iberian Peninsula. The first one occurred from August 11 to August 13, 2025, and the second one between August 15 and August 17, 2025. In both periods, maximum temperatures of more than 45 °C were measured. In France, the highest observed temperature during the recent heatwave was 43.4 °C in Argeliers on August 10, 2025.
In Germany, the maximum temperatures were far less extreme than in Southern Europe. In Kitzingen, BY, a maximum temperature of 37.1 °C was recorded on August 15, 2025. As such the peak temperature of the recent heat wave was much lower than the peak temperature of the heat wave in late-June and early-July where temperatures of up to 39.3 °C were measured in Germany. In the southernmost parts of Germany, up to 9 consecutive days with maximum temperatures of more than 30 °C were recorded. Especially in the second heat peak, from August 12 to August 15, 2025, heat stress levels further increased due to high overnight low temperatures. Notably, in the night from August 14 to August 15, 2025, temperatures remained above the 20 °C mark in many areas in Western Germany.
Atop of the Brocken Mountain, a maximum temperature of 29.5 °C was recorded on August 14, 2025. This is the highest recorded temperature on the mountain observatory in August since record-keeping began in August of 1896. The previous record from August 2012 was beaten by 0.5 K. In the night to August 15, 2025, severe thunderstorms developed over an area to the northeast of Bielefeld, NW. Within a few hours, radar-indicated precipitation totals reached more than 100 mm. Localized flash flooding was reported from the affected area.
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Hourly radar-indicated precipitation totals over Germany, 14.08.2025 20 UTC - 15.08.2025 00 UTC, source:
Wettergefahren-Frühwarnung
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On August 19, 2025, a small upper-level trough moved towards Central France. Ahead of the trough, temperatures reached up to 31.9 °C in Germany. The related surface low brought heavy rains to the southernmost part of Germany. 48 h precipitation totals along the Northern Alps and the Southern Black Forest reached more than 100 mm. On August 20, 2025, the city of Freiburg recorded a daily precipitation total of 77.7 mm. Since record-keeping began in August of 1949, this is the highest daily precipitation total in the month of August recorded at the measuring site.
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Daily precipitation totals over Germany, 20.08.2025 (left), 21.08.2025 (middle), and 2-day precipitation totals over Germany, 20.08.2025 - 21.08.2025, source:
Wettergefahren-Frühwarnung
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During the recent heat wave, large forest fires developed in Southern Europe. Most notably, northwestern Spain is affected by severe forest fires. More than 4,000 km² were burnt in Spain in this year thus far. The severity of these forest fires is fueled by a large vegetation build-up across the peninsula due to an unusually wet spring. Due to the typical summer dryness of a Mediterranean climate, this provides prime conditions for severe forest fires to develop. At least two fatalities were reported from the affected areas.
Visible satellite imagery of the active wildfires in Northwestern Spain, 17.08.2025 (left), source:
Copernicus - Image of the day Credit: European Union, Copernicus Sentinel-2 imagery
and year-to-date burnt area in Spain until 19.08.2025 (right), EFFIS
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The recent heat wave was intense and long-lasting in Western and Central Europe. Daily temperature deviations reached more than 10 K. Since mid-June 2025, maximum temperatures in Germany reached 30 °C on nearly every day. With a mean temperature of 18.3 °C, June 2025 was the seventh warmest on record in Germany with a temperature deviation of 2.0 K. After a short interlude in the second week of July 2025, the sub-seasonal temperature forecasts for Europe hint at well-above-average temperatures for most of July and early August 2025. The medium-range NWP forecasts for Europe already show the potential for another major heat wave in the third week of July 2025.
Text: KG
August 22, 2025
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