Climate averages 1991–2020
Basel weather
in September.
A mild, wet month: the 4th warmest and the 6th driest of the year.
Long-term climate patterns, not a forecast for a particular trip.
September is a mild month in Basel: daytime highs average 20.1°C and nights cool to about 10.8°C. By daytime temperature it is the 4th warmest of the 12 months.
Expect about 95 mm of rain on roughly 13 days, which makes September a wet month (the 6th driest of the 12 months). Daylight, from sunrise to sunset, lasts about 12 h 37 min on an average September day.
The nearest other city in this atlas is Mulhouse (28 km away). In September its highs average 19.7°C, about as warm as Basel, with 74 mm of rain.
Among the 8 cities listed in Switzerland, Basel ranks 1st of 8 for the warmest September highs and 3rd of 8 for the driest September (rainfall, lowest first). The mean September high of those 8 cities is 18.8°C; Basel is 1.3°C warmer than that mean.
From September to October, average highs fall by 4.7°C to 15.4°C, and monthly rainfall rises from 95 mm to 97 mm.
The annual picture
September in context
Monthly rainfall
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Basel climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 5.4°C-1.7°C | -1.7°C | 80 | 13.5 | 8.99 h |
| February | 6.9°C-1.5°C | -1.5°C | 73 | 11.7 | 10.210 h |
| March | 11.1°C1.4°C | 1.4°C | 83 | 13.5 | 11.912 h |
| April | 15.0°C4.6°C | 4.6°C | 90 | 14.1 | 13.614 h |
| May | 18.7°C8.9°C | 8.9°C | 129 | 16.8 | 15.115 h |
| June | 22.3°C12.7°C | 12.7°C | 118 | 15.8 | 15.916 h |
| July | 24.5°C14.8°C | 14.8°C | 121 | 15.4 | 15.616 h |
| August | 24.5°C14.9°C | 14.9°C | 125 | 15.1 | 14.314 h |
| September, selected | 20.1°C10.8°C | 10.8°C | 95 | 12.6 | 12.613 h |
| October | 15.4°C6.7°C | 6.7°C | 97 | 13.2 | 10.911 h |
| November | 9.4°C2.1°C | 2.1°C | 94 | 13.0 | 9.49 h |
| December | 5.8°C-0.8°C | -0.8°C | 101 | 14.1 | 8.59 h |
Rainfall is the average of the 30 separate monthly totals. A rain day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
September in nearby cities
- Mulhouse in SeptemberFrance · 28 kmHigh 19.7°C · Low 11.2°C · 74 mm rain
- Freiburg in SeptemberGermany · 53 kmHigh 20.0°C · Low 11.8°C · 77 mm rain
- Bern in SeptemberSwitzerland · 69 kmHigh 17.7°C · Low 9.6°C · 88 mm rain
- Zürich in SeptemberSwitzerland · 76 kmHigh 18.9°C · Low 11.2°C · 123 mm rain
- Luzern in SeptemberSwitzerland · 79 kmHigh 18.9°C · Low 11.6°C · 166 mm rain
- Winterthur in SeptemberSwitzerland · 87 kmHigh 18.7°C · Low 10.8°C · 91 mm rain
- Villingen-Schwenningen in SeptemberGermany · 89 kmHigh 16.9°C · Low 8.9°C · 93 mm rain
- Strasbourg in SeptemberFrance · 115 kmHigh 20.1°C · Low 11.6°C · 70 mm rain
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for Basel) is explained once on the Basel year overview and on the Sources, method and limits page.