Aarau weather in September

In September, Aarau sees average daytime highs of 18°C and overnight lows near 10°C, with 108 mm of rain across 13.2 wet days and about 12.4 hours of daylight. It is the 4th-warmest and 6th-wettest month of the year here.

Highs ease over the month, from about 20°C in the first days to 16°C by the end. The sky is clear or mostly clear about 25% of the time in September, and the air most often feels dry.

Daylight stretches from about 13 h 12 min at the start of September to 11 h 30 min by month's end. Set against the rest of the year, September is Aarau's 3rd-clearest and 11th-windiest month. For the whole year in context, see Aarau's year-round climate.

Daytime high
18°
4th warmest
Overnight low
10°
9th coldest
Rainfall
108 mm
13.2 wet days
Daylight
12 h 18 min
6:12 AM – 6:32 PM
Cloud cover
62%
3rd clearest
Wind
7 km/h
11th windiest
Solar energy
3.54 kWh/m²
Travel score
5.3
out of 10

Aarau is capital of Canton Aargau, Switzerland.

Air quality
Good
PM2.5 8.9 µg/m³ · 2020
Density
1,743/km²
people per km²
Founded
1240

Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.

Temperature in September

Average highAverage lowShaded bands: 10–90% of days

Highs ease over the month, from about 20°C in the first days to 16°C by the end.

A typical September day in Aarau reaches about 18°C in the afternoon and slips back to 10°C overnight — a 8°C spread between the day's warmth and the night's chill. On most days the high lands between 13°C and 24°C. Set against its neighbours, September runs about 4°C cooler than August and about 5°C warmer than October.

10°20°30°151015202530
Avg high (°C)Avg low (°C)
12112
22012
32011
42011
52011
62011
72011
82011
91911
101911
111910
121910
131910
141910
151910
161810
171810
181810
19189
20189
21189
22179
23179
24179
25179
26179
27179
28169
29169
30168

How September really feels in Aarau

Once humidity and wind are folded in, September averages 0 days that feel above 32°C and 0 that feel at or below 0°C — the comfort signal a plain temperature reading hides.

Days feeling ≥ 32°C
0
heat index over the day's high
Days feeling ≤ C
0
wind chill below the day's low

September sits comfortably in between — no days that feel dangerously hot or drop to a hard freeze once humidity and wind are folded in.

Aarau weather by month

How September compares with the rest of the year at a glance. September is the 4th-warmest and 6th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysSnow daysDaylight (hours)Travel score
Jan / -2°9713.478.70.0
Feb / -1°8010.96.49.90.2
Mar10° / 9714.24.411.61.9
Apr14° / 10014.52.113.33.5
May18° / 14817.3014.94.7
Jun21° / 12°14217.4015.75.4
Jul23° / 14°15217015.35.9
Aug23° / 13°14516.5014.15.9
Sep18° / 10°10813.2012.45.3
Oct13° / 10313.20.310.63.4
Nov / 10013.13.39.10.9
Dec / -1°11614.36.78.30.0

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 25% of the time in September.

Beyond those clear spells, partly cloudy skies cover about 16% of September, with mostly cloudy or overcast conditions the remaining 59%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
14753
24753
34753
44753
54753
64753
74654
84654
94654
104456
114456
124357
134357
144357
154258
164159
174159
184060
194060
203961
213862
223862
233862
243763
253763
263763
273664
283664
293466
303367

Chance of precipitation in September

Any precipitation

Aarau gets around 108 mm of rain over 13.2 wet days in September. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 45% and peaks near 47% on the wettest days.

0%20%40%60%151015202530
Rain chance (%)
147
247
346
446
546
646
746
846
946
1046
1146
1246
1346
1445
1545
1645
1745
1845
1944
2044
2144
2244
2344
2444
2544
2645
2745
2846
2947
3047

Humidity in September

DryComfortableHumidMuggyOppressiveMiserable

Most of September feels dry — the stacked bands show each day's mix of comfort levels, read off the dew point.

By dew point, September lands in the dry band about 77% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)
1612910
263289
365278
467267
568266
669265
770255
871254
972253
1073243
1173243
1274242
1375232
1476231
1576231
1677221
1778211
1878211
1980200
2081190
2182180
2283170
2384160
2486140
2587130
2688120
2788120
2889110
2990100
309190

Wind in September

Winds average 7 km/h in September.

Across September, daily wind ranges from about 7 km/h on the calmest days to 7 km/h at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (km/h)Feels
17calm
27calm
37calm
47calm
57calm
67calm
77calm
87calm
97calm
107calm
117calm
127calm
137calm
147calm
157calm
167calm
177calm
187calm
197calm
207calm
217calm
227calm
237calm
247calm
257calm
267calm
277calm
287calm
297calm
307calm

Sunrise & sunset in September

DaylightNight

Daylight runs from about 13 h 12 min at the start of September to 11 h 30 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 102 minutes over September. Sunrise moves from 5:51 AM to 6:32 AM, and sunset from 7:04 PM to 6:03 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.25:517:04
213.15:537:02
313.15:546:59
413.05:566:57
513.05:576:55
612.95:586:53
712.96:006:51
812.86:016:49
912.76:026:47
1012.76:046:45
1112.66:056:43
1212.66:076:41
1312.56:086:39
1412.56:096:36
1512.46:116:34
1612.36:126:32
1712.36:136:30
1812.26:156:28
1912.26:166:26
2012.16:186:24
2112.06:196:22
2212.06:206:19
2311.96:226:17
2411.96:236:15
2511.86:256:13
2611.86:266:11
2711.76:276:09
2811.66:296:07
2911.66:306:05
3011.56:326:03

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 3.54 kWh/m².

For context, solar energy here swings from a low near 1 kWh/m² to a high of 5.61 kWh/m² in June across the year — September's 3.54 kWh/m² falls in the middle.

012345151015202530
Solar energy (kWh/m²)Level
14.2Bright
24.1Bright
34.1Bright
44.1Bright
54.0Bright
64.0Moderate
73.9Moderate
83.9Moderate
93.8Moderate
103.8Moderate
113.8Moderate
123.7Moderate
133.7Moderate
143.6Moderate
153.6Moderate
163.5Moderate
173.5Moderate
183.4Moderate
193.4Moderate
203.3Moderate
213.3Moderate
223.2Moderate
233.2Moderate
243.1Moderate
253.1Moderate
263.0Moderate
273.0Moderate
282.9Moderate
292.9Moderate
302.8Moderate
Planning a trip in September

Is September a good time to visit Aarau?

Our two travel scores rate September for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal).

5.3
Sightseeing
4th-best month of the year
2.0
Beach & pool
4th-best month of the year

September is a reasonable time to visit Aarau for sightseeing.

What to pack for Aarau in September

From September's temperature range, rain chance, sun and wind — what's worth putting in the bag.

In September, Aarau sees daytime highs around 18°C and nights near 10°C. Pack rain gear. About 13 days see rain.

rain gear

UV index in Aarau in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 4 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Aarau peaks around July 15 at about 8 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near January 1 at about 1 (low).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 8 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecLowModerateHighVery highHighModerateLowJul 15UV 8Jan 1UV 1
UV index (midday)Level
Jan1Low
Feb2Moderate
Mar4Moderate
Apr5Moderate
May7High
Jun7Very high
Jul8Very high
Aug7High
Sep4Moderate
Oct3Moderate
Nov2Low
Dec1Low
Location & terrain

Where is Aarau?

Aarau sits at 47.4°N, 8.0°E, 389 m above sea level, in Switzerland. The nearest listed city is Olten, 12 km away.

Bad SäckingenBadenWettingenDietikonRheinfeldenWaldshut-TiengenZürich (Kreis 9)

Topography around Aarau

How much the land rises and falls, and what covers it, within 3, 16 and 80 km of Aarau.

Within 3 km, the terrain around Aarau has only modest variations in elevation — a maximum elevation change of 198 m around an average of 416 m above sea level; within 16 km, large variations in elevation — a maximum elevation change of 695 m; within 80 km, extreme variations in elevation — a maximum elevation change of 2,987 m.

The land around Aarau is covered by trees (48%) and artificial surfaces (26%) within 3 km, trees (50%) and grassland (24%) within 16 km, and trees (47%) and grassland (28%) within 80 km.

3 km
198 m
16 km
695 m
80 km
2,987 m
treesgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: Olten 12 km · Bad Säckingen 19 km · Baden 22 km · Wettingen 23 km · Dietikon 27 km · Rheinfelden 27 km · Waldshut-Tiengen 29 km · Zürich (Kreis 9) 33 km

Switzerland travel facts

Travel advisory
Level 1
Exercise Normal Precautions
Power plugs
Type C / J
230 V · 50 Hz
Prices
≈ 112% of US
price level, 2025
GDP per capita
$114,769
2025
Happiness
7.0 / 10
World Happiness, 2025
Safe drinking water
97%
of population, 2024
Homicide rate
0.6
per 100k, 2023
Road deaths
2.2
per 100k/yr, 2019
Income group
High
World Bank
English
High
EF EPI 564
Religion
Roman Catholic 34%none 29%Protestant 23%other Christian 6%

Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.

Data sources

Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Aarau (47.3925°, 8.0442°, elevation 389 m), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).