The summer of 2003 went down in the weather annals as the summer of the century. Especially the heat wave in August was very exceptional. This year it looks quite different at the moment: We are heading for a cool phase for August, but next week it should be hot from the middle of the week.
Heat summer marks 20th anniversary
It has already been 20 years since the heatwave of the century in 2003. In total, the summer of 2003 was more than 4.5 degrees warmer than the long-term average for the years 1961 to 1990 and more than 3 degrees warmer than the average for 1991 to 2020. After that, we did not reach the heat summer of 2003 by far, the second hottest summer was last summer with a deviation of about 2.35 degrees compared to the average 1991 to 2020. This year we are about 1.8 degrees warmer than the long-term average 1991 to 2020 (see Fig. 1).
Fig. 1: Temperature deviation of previous summer 2023 compared to long-term average 1991 to 2020; Source: MeteoNews, UBIMET
The mean will drop a bit more in the coming days with the below-average temperatures, so we are unlikely to get quite close to the hottest summers even if it gets very hot again in the course of August. In any case, the heat returns to us from about the middle of next week (see yesterday's blog).
Historic 40.5 (41.5) degrees in Grono on August 11, 2003
On August 11, 2003, the weather hut of MeteoSwiss in Grono showed 41.5 degrees above 40 degrees for the first time in Switzerland. Subsequently, this value was not nearly reached again. However, the measurement is doubted because it was made in a classical weather hut and not with an electronic sensor. After a correction procedure, this measured value is now listed as 40.5 degrees. Geneva came closest to this value with 39.7 degrees on July 7, 2015.
Heat days without end
The summer of 2003 was also characterized by long-lasting heat waves (days with 30 degrees and more). These occurred especially in June and in the first half of August, where the highest temperatures of the summer were also measured. In particular, it was very hot around August 10. Locarno was the leader in the total number of hot days for the entire summer, with a total of 56 (normal is about 17).
Stable omegas responsible for heat
The heatwave summer of 2003 was caused by a stable omega-temperature system, which regenerated itself again and again and thus brought great heat to us in spurts. Not only Switzerland was affected, but also large parts of Central and Southern Europe (see Fig. 2).
Fig. 2: Temperature deviation summer 2003 compared to long-term average; Source: Wikipedia
And in the future?
The trend towards hotter summers is unmistakable in the long series of measurements (cf. Fig. 3), and a summer like 2003 is becoming more likely.
Fig. 3: Average summer temperatures compared to the long-term average 1991 to 2020; Source: meteostats.ch
It is only a matter of time before the 40 degree mark is broken in the north. It is also to be expected that in the future we will have to live with increasingly frequent and longer heat waves similar to this summer in the Mediterranean region.