A special weather situation has set in, we are in the sphere of influence of an omega high. It will shape our weather for the whole week. Meteorologically, this sounds almost boring, and yet the current situation holds some remarkable peculiarities!
Highest mountain stations with new September records
Also today, Tuesday, it wasexceptionally warm for the time of year, but with the exception of the three highest mountain stations(Jungfraujoch, Corvatsch and Weissfluhjoch) no September records could be set at the official stations (see the table at the end of this article).
At low altitudes, the heat mark of 30 degrees was broken in Sion, where 31.4 degrees were recorded, making it the fourth warmest September day since measurements began (see Fig. 1). Otherwise, the 30 degree mark was missed, but in some cases only just.
Highest temperature (as of 17:10)
| Measuring stations | Highest temperature (in °C) |
|---|---|
| Sion (482 a.s.l., VS) | 31.4 |
| Basel-Binningen (316 a.s.l., BL) | 29.9 |
| Evionnaz (480 a.s.l., VS) | 29.2 |
| Visp (640 a.s.l., VS) | 29.2 |
| Bern-Belpmoos (510 a.s.l., BE) | 29.0 |
| Geneva (420 a.s.l., GE) | 28.8 |
| Thierachern (570 a.s.l., BE) | 28.8 |
| Delémont (439 a.s.l., JU) | 28.7 |
| Payerne (490 a.s.l., VD) | 28.6 |
| Mühleberg (483 a.s.l., BE) | 28.6 |
| Möhlin (308 a.s.l., AG) | 28.6 |
| Bière (684 a.s.l., VD) | 28.6 |
| Nyon (430 a.s.l., VD) | 28.5 |
| Bagnes (820 a.s.l., VS) | 28.5 |
| Würenlingen (334 a.s.l., AG) | 28.3 |
| Mathod (435 a.s.l., VD) | 28.1 |
| Koppigen (484 a.s.l., BE) | 28.1 |
| Courtelary (685 a.s.l., BE) | 28.0 |
| Wynau (422 a.s.l., BE) | 28.0 |
| Grenchen (430 a.s.l., SO) | 27.9 |
Several new September records
Already in the morning, the temperature on Mount Pilatus exceeded 20 degrees for the first time in September since measurements began, and in the end it improved the old record from 1987 by a whole 2 degrees! Ulrichen also reached unimagined heights. With a maximum of 29.9 degrees, this Monday was by far the warmest September day in the series of measurements, the old record was exceeded by 2.5 degrees and thus virtually pulverized. Ulrichen was the second warmest station in Switzerland behind Sion with 30.2 degrees, closely followed by Visp with 29.8 degrees. Such a position is also a novelty for the village in the Obergoms! The many other September records can be found in the detailed table at the end of this article, which will be updated continuously in the coming days.
Fig. 1: Maximum temperatures on September 4, 2023; Source: MeteoNews, Ubimet
Late summer temperatures and pure sun
Yesterday, Sunday, the sky was still covered with extensive high clouds, and this morning there were still some of them, especially in the west. Now, however, these high clouds are moving away to the west, and the last early morning fog patches are clearing. The afternoon brings a lot of blue sky. Temperatures will rise to 26 to 28 degrees, locally to 29 degrees.
Fig. 1: View from the Rigi in the early morning; Source: Roundshot
And it will continue in this form until next weekend! In the morning, there will be a few patches of early morning fog, which will dissipate in the morning. Otherwise, the sun will shine brightly and, apart from a few clouds, the sky will be blue. Only in Ticino will the sun have a hard time tomorrow, here there will be high fog-like clouds. The maximum temperatures will tend to rise slightly in the course of the week, but with 28 to 30 degrees it will hardly be enough for new records at low altitudes. For this, there is too little wind, which would support the already noticeably lower sun in mixing the air. The air mass itself, however, is really thick behind the ears!
Fig. 2: Outlook for the coming days; Source: MeteoNews
Record-breaking air mass
On the mountains it is exceptionally warm! Last night, a zero degree limit of 5253 meters was registered at the radiosonde ascent in Payerne. This was only the 4th time in the history of measurements since 1954 that the zero degree limit was above 5000 meters, but after the record of August 21 (5298 meters) already the 2nd time this year alone! And according to the current state of the models, the sounding should result in a value above 5000 meters also in the next two nights. This mark was until now the great exception, this year obviously no more!
Record-breaking are so in the first place the mountain temperatures. And indeed, already in the morning on Mount Pilatus the old September record fell! This was 19.4 degrees and was from 14.9.1987, today at 10 o'clock the measured value was already 20.2 degrees, at 11 o'clock it was 21.0 degrees. The end of the line has not yet been reached. Today and in the coming days , more mountain stations should deliver new monthly records, occasionally even all-time records are not completely out of the question. We will report here.
| Station | September record | Date | New record |
| Napf (1406 m above sea level) | 25.7 degrees | 14.9.1987 | |
| Chasseral (1596 m a.s.l.) | 22.7 degrees | 17.9.1987 | |
| Cimetta (1663 m a.s.l.) | 24.6 degrees | 5.9.2006 | |
| Arosa (1880 m a.s.l.) | 23.8 degrees | 13.9.1943 | |
| Buffalora (1973 m a.s.l.) | 22.5 degrees | 4.9.1982 | |
| Le Moléson (1976 m a.s.l.) | 21.2 degrees | 5.9.2006 | |
| Grimsel Pass (1988 m a.s.l.) | 20.0 degrees | 4.9.1973 | |
| Pilatus (2107 m a.s.l.) | 19.4 degrees | 14.9.1987 | 21.0 degrees |
| Gütsch above Andermatt (2287 m a.s.l.) | 22.3 degrees | 13.9.1999 | |
| Berninapass (2272 m a.s.l.) | 20.0 degrees | 16.9.1987 | |
| Col du Grand St-Bernard (2479 m a.s.l.) | 19.1 degrees | 14.9.1987 | |
| Säntis (2504 m a.s.l.) | 17.6 degrees | 6.9.2006 | |
| Weissfluhjoch (2694 m a.s.l.) | 18.1 degrees | 18.9.1975 | |
| Corvatsch (3297 m a.s.l.) | 10.3 degrees | 18.9.2003 | |
| Jungfraujoch (3582 m a.s.l.) | 10.8 degrees | 11.9.2018 |
