The first half of October was partly record warm in Switzerland, much too dry and much too sunny. In the south, there has been no precipitation at all in many places. In addition, there was already more sunshine in the Central Plateau than otherwise on average in the whole of October. The interim balance of the so far very unusual month.
So far more than 4 degrees too warm!
Similar to the first half of September, the map with the temperature deviation for the first half of October appears in shades of red, indicating a large temperature surplus (see Fig. 1). Thus, it was 4.3 degrees too warm in October seen over the whole of Switzerland so far.
Fig. 1: Temperature deviation so far in October compared to the long-term average 1991-2020; Source: MeteoNews, UBIMET
In places the deviation in the mountains and in the Jura is over 5 degrees, on La Dôle it is even 6 degrees! Thus, it was in many places the warmest first half of October since the beginning of measurements! Especially in the lowlands and in the alpine valleys, the temperature surplus is somewhat lower, for which the strong radiation during the often clear nights was responsible. Thus, the map with the temperature minima shows a deviation of 2.9 degrees and in the lowlands partly only a slight deviation from the long-term mean, while the temperature maxima seen over the whole of Switzerland were 6 degrees higher than normal (cf. Figs. 2 and 3).
Fig. 2: Deviation of temperature minima so far in October compared to the long-term mean 1991-2020; Source: MeteoNews, UBIMET
Fig. 3: Deviation of temperature maxima so far in October compared to the long-term mean 1991-2020; Source: MeteoNews, UBIMET
It is noticeable that the temperature maxima are lower in the Alpine valleys than in the lowlands. This may be a consequence of the fact that fog hardly ever dampened the temperature maxima on the Central Plateau, whereas in other years this has occurred from time to time in the first half of October.
New October temperature records in places
The temperatures were not only exceptionally high, but also several new October records were set, both in the lowlands and in the mountains. Occasionally, records were also broken at stations with very long measurement series, such as in Bern (data since 1864), in Samedan (data since 1869) or in Lucerne (data since 1886).
Extraordinary number of summer days
In October temperatures of 25 degrees and more and thus summer days normally occur extremely rarely, for example in Basel-Binningen on average only three times in ten years. In this October alone there were 9(!) summer days. In Bern, there was only one summer day in 158 years from the beginning of measurements in 1864 until this year's October, but in October so far, five summer days were recorded (see Fig. 4).
Fig. 4: Number of summer days so far in October; Source: MeteoNews, UBIMET
It is no wonder that there has not been a single frost day in October in the lowlands and in the lower Alpine valleys (minima below 0 degrees).
Temperatures as normally in September
Temperatures so far in October have been at levels normally seen in September. For example, the average temperature in Basel-Binningen until October 15 is 15.5 degrees, which is pretty much the long-term average from 1991 to 2020 (15.4 degrees). The same is true for the mountains, on Säntis the average temperature up to October 15 was 6.2 degrees, exactly the same as the long-term September average.
Partly extremely dry
The first half of October, which was primarily characterized by high pressure, was much too dry in most parts of the country, with a deficit of about 75% (see Fig. 5).
Fig. 5: Precipitation deviation so far in October compared to the long-term average 1991-2020; Source: MeteoNews, UBIMET
South of the Alpine ridge and partly in southern Valais, there has been no precipitation at all so far in October (cf. fig. 6). However, this will change soon, especially on Friday a lot of precipitation is expected in these regions (cf. here).
Fig. 6: Rainfall total so far in October; Source: MeteoNews, UBIMET
Much too sunny
The first half of October was not only much too warm and too dry, but also much too sunny, nationwide the surplus amounts to about 68% (cf. fig. 7). Especially on the Central Plateau it was exceptionally sunny, locally there was more than twice as much sun as usual. In many places on the Central Plateau the sunshine duration is already higher than the average for the whole of October (e.g. in Neuchâtel 140 hours so far, average in October 108 hours or in Buchs/Aarau 109 hours so far, average in October 86 hours). The reason why the deviation of the sunshine duration is greatest in the Central Plateau is that there was hardly any fog.
Fig. 7: Deviation of sunshine duration so far in October compared to the long-term average 1991-2020; Source: MeteoNews, UBIMET
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