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Persistent ridges over Central Europe led to the warmest September in recorded history in Central Europe, with an average temperature of 17.29 °C in Germany. Temperature deviations across Central Europe reached more than 3 K, as the previous record monthly average was surpassed by nearly 0.4 K in Germany.
After the second half of August 2023 was dominated by heat waves, especially in the southern part of Germany and the Alpine region. The first half of September 2023 was yet again dominated by very strong ridges expanding across Central Europe, advecting very warm air masses from southwesterly directions. 850 hPa temperatures reached more than 20 °C. More than 10 consecutive summer days were recorded in the first half of September. The September heat wave reached its peak on September 11 and September 12, 2023, where day-time maximum temperatures reached up to 33.3 °C in Waghäusel-Kirrlach, BW. Just 1.5 K shy of the all-time September temperature record in Germany set in 2020.
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30-day mean 500 hPa geopotential over Europe and 30-day 500 hPa geopotential anomaly over Europe (left) and 30-day mean sea level pressure over Europe and 30-day sea level pressure anomaly over Europe (right), 30.09.2023, source:
PSL NOAA
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Throughout the month up to 10 days with temperatures of more than 30 °C were recorded at the weather station in Waghäusel-Kirrlach, BW. Most days with day-time maximum temperatures above the 25 °C-mark were recorded at the weather stations in Müllheim, BW, Waghäusel-Kirrlach, BW, and Rheinfelden, BW with 21 out 30 days in September. This made the September 2023 to feel more like the fourth summer month of this year rather than the first month of autumn. Only in a few locations in the hills in Central and Southern Germany recorded nights with below-freezing temperatures near the surface. In comparison, on 3 days the temperatures failed to drop below 20 °C at the weather stations at Weinbiet, RP.
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Daily temperature deviations at the weather station in Rheinstetten, BW, 03.10.2022 - 02.10.2023, source:
DWD
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The second half of September was once again dominated by strong ridges expanding across Central Europe, with temperatures staying below the 30 °C-mark in Germany. Though, during this period most of the precipitation of the month were observed. Nevertheless, most weather stations in Germany recorded well-below-average precipitation with the nationwide average reaching only 50 % of the monthly average. The most precipitation fell in North Rhine-Westphalia and the northern part of Rhineland-Palatine, while parts of Bavaria and Eastern Germany only received 10 - 30 % of the monthly average.
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Monthly temperature deviation (left), precipitation deviation (middle), and sunshine deviation (right) over the Germany for the month of September 2023, source:
DWD
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In Western Germany, most of the precipitation fell during the passage of strong thunderstorms. Even a tornado was observed in the second half of September, hitting a small village in the Eifel mountains. Nevertheless, the September 2023 brought also well-above-average sunshine hours, with more than 160 % of the monthly average, with the highest deviations being observed in Western Germany. Temperature deviations were the highest, at the weather stations at mountain tops both in the Central German countryside as well as in the Alps. The observatory at the Zugspitze recorded also the warmest September in the recorded history, with a temperature average 5.5 °C. Concurrently, the lowest temperature deviations were observed at fog-prone weather stations in river valley, were the fog prevented some diurnal insolation.
Text: KG
October 03, 2023
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