Montesson weather in September

In September, Montesson sees average daytime highs of 20°C and overnight lows near 11°C, with 44 mm of rain across 8.6 wet days and about 12.4 hours of daylight. It is the 4th-warmest and 12th-wettest month of the year here.

Highs ease over the month, from about 22°C in the first days to 19°C by the end. The sky is clear or mostly clear about 22% of the time in September, and the air most often feels dry.

Daylight stretches from about 13 h 18 min at the start of September to 11 h 30 min by month's end. Set against the rest of the year, September is Montesson's 3rd-clearest and 9th-windiest month. For the whole year in context, see Montesson's year-round climate.

Daytime high
20°
4th warmest
Overnight low
11°
9th coldest
Rainfall
44 mm
8.6 wet days
Daylight
12 h 24 min
6:35 AM – 6:56 PM
Cloud cover
64%
3rd clearest
Wind
12 km/h
9th windiest
Solar energy
3.42 kWh/m²
Travel score
6.4
out of 10

Temperature in September

Average highAverage lowShaded bands: 10–90% of days

Highs ease over the month, from about 22°C in the first days to 19°C by the end.

A typical September day in Montesson reaches about 20°C in the afternoon and slips back to 11°C overnight — a 9°C spread between the day's warmth and the night's chill. On most days the high lands between 16°C and 25°C. Set against its neighbours, September runs about 4°C cooler than August and about 5°C warmer than October.

10°15°20°25°30°151015202530
Avg high (°C)Avg low (°C)
12213
22213
32212
42212
52212
62212
72112
82112
92112
102112
112112
122112
132111
142111
152011
162011
172011
182011
192011
202011
212011
222011
231911
241911
251910
261910
271910
281910
291810
301810

How September really feels in Montesson

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.

Montesson weather by month

How September compares with the rest of the year at a glance. September is the 4th-warmest and 12th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysSnow daysDaylight (hours)Travel score
Jan / 5511.70.98.50.7
Feb / 4910.11.29.81.2
Mar12° / 5110.30.611.62.9
Apr15° / 5110.80.113.44.4
May18° / 6411.10155.6
Jun22° / 12°569.9015.96.4
Jul24° / 14°529.2015.57.0
Aug24° / 14°579.4014.26.9
Sep20° / 11°448.6012.46.4
Oct16° / 6211010.54.6
Nov10° / 5911.40.38.92.2
Dec / 7112.60.98.10.9

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 22% 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 62%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
13961
23961
33961
44060
53961
63961
73961
83862
93961
103961
113961
123961
133961
143961
154060
164060
174060
184060
194060
204060
214060
223961
233961
243862
253862
263664
273466
283466
293268
303169

Chance of precipitation in September

Any precipitation

Montesson gets around 44 mm of rain over 8.6 wet days in September, the driest month. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable rain averages around 29% and peaks near 36% on the wettest days. The odds climb toward the end of the month.

0%10%20%30%40%50%151015202530
Rain chance (%)
126
226
326
425
526
626
726
826
927
1027
1127
1228
1328
1428
1529
1629
1729
1830
1930
2030
2131
2231
2331
2432
2533
2633
2734
2835
2936
3036

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 70% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)
15829121
25829121
36128110
46228100
56228100
6642790
7642790
8652780
9662680
10672670
11682570
12682570
13702460
14712360
15722350
16732250
17742240
18742240
19742240
20752230
21752230
22752230
23762220
24752320
25752320
26752320
27752320
28752320
29762220
30762220

Wind in September

Winds average 12 km/h in September.

Across September, daily wind ranges from about 11 km/h on the calmest days to 12 km/h at its breeziest. It stays fairly steady from day to day.

051015151015202530
Wind speed (km/h)Feels
111calm
211calm
311calm
411calm
511calm
611calm
711calm
812calm
912calm
1012calm
1112calm
1212calm
1312calm
1412calm
1512calm
1612calm
1712calm
1812calm
1912calm
2012calm
2112calm
2212calm
2312calm
2412calm
2512calm
2612calm
2712calm
2812calm
2912calm
3012light breeze

Sunrise & sunset in September

DaylightNight

Daylight runs from about 13 h 18 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 108 minutes over September. Sunrise moves from 6:13 AM to 6:56 AM, and sunset from 7:29 PM to 6:26 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.36:137:29
213.26:157:27
313.16:167:25
413.16:187:23
513.06:197:21
613.06:207:18
712.96:227:16
812.86:237:14
912.86:257:12
1012.76:267:10
1112.76:287:07
1212.66:297:05
1312.56:317:03
1412.56:327:01
1512.46:346:59
1612.46:356:56
1712.36:376:54
1812.26:386:52
1912.26:406:50
2012.16:416:48
2112.06:436:45
2212.06:446:43
2311.96:466:41
2411.96:476:39
2511.86:486:36
2611.76:506:34
2711.76:516:32
2811.66:536:30
2911.66:546:28
3011.56:566:26

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 3.42 kWh/m².

For context, solar energy here swings from a low near 0.76 kWh/m² to a high of 5.55 kWh/m² in June across the year — September's 3.42 kWh/m² falls in the middle.

012345151015202530
Solar energy (kWh/m²)Level
14.0Bright
24.0Bright
34.0Moderate
43.9Moderate
53.9Moderate
63.8Moderate
73.8Moderate
83.7Moderate
93.7Moderate
103.6Moderate
113.6Moderate
123.6Moderate
133.5Moderate
143.5Moderate
153.5Moderate
163.4Moderate
173.4Moderate
183.3Moderate
193.3Moderate
203.2Moderate
213.2Moderate
223.1Moderate
233.1Moderate
243.0Moderate
253.0Moderate
262.9Moderate
272.9Moderate
282.8Moderate
292.8Moderate
302.7Moderate
Planning a trip in September

Is September a good time to visit Montesson?

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

6.4
Sightseeing
3rd-best month of the year
3.5
Beach & pool
4th-best month of the year

September is a reasonable time to visit Montesson for sightseeing.

What to pack for Montesson in September

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

In September, Montesson sees daytime highs around 20°C and nights near 11°C. Worth packing: rain gear. About 9 days see rain.

rain gear

UV index in Montesson 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 Montesson peaks around June 22 at about 7 (high) — sunscreen and a hat are worth it in the middle of the day. 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 7 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecLowModerateHighModerateLowJun 22UV 7Jan 1UV 1
UV index (midday)Level
Jan1Low
Feb2Low
Mar3Moderate
Apr5Moderate
May6High
Jun7High
Jul7High
Aug7High
Sep4Moderate
Oct3Moderate
Nov1Low
Dec1Low

Air quality in Montesson in September

GoodModeratePoorUnhealthyVery unhealthy

Average fine-particle pollution (PM2.5) through the year — so you can see where September falls, not just the annual average.

Air quality in Montesson is worst in April — around 20 µg/m³ PM2.5 (moderate), and holds fairly steady the rest of the year.

Modeled monthly averages (CAMS reanalysis, 2015–2024).

0102030JanFebMarAprMayJunJulAugSepOctNovDecModerateApr 1020 µg/m³Jul 2014 µg/m³
PM2.5 (µg/m³)Level
Jan17Moderate
Feb17Moderate
Mar20Moderate
Apr20Moderate
May17Moderate
Jun16Moderate
Jul13Moderate
Aug14Moderate
Sep15Moderate
Oct15Moderate
Nov15Moderate
Dec15Moderate
Location & terrain

Where is Montesson?

Montesson sits at 48.9°N, 2.1°E, 37 m above sea level, in France. The nearest listed city is Le Vésinet, 2.0 km away.

Topography around Montesson

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

Within 3 km, the terrain around Montesson has only modest variations in elevation — a maximum elevation change of 81 m around an average of 43 m above sea level; within 16 km, only modest variations in elevation — a maximum elevation change of 206 m; within 80 km, significant variations in elevation — a maximum elevation change of 265 m.

The land around Montesson is covered by trees (45%) and artificial surfaces (35%) within 3 km, trees (42%) and artificial surfaces (39%) within 16 km, and cropland (53%) and trees (32%) within 80 km.

3 km
81 m
16 km
206 m
80 km
265 m
treesgrasslandcroplandartificial surfaceswater
September weather nearby: Le Vésinet 2.0 km · Chatou 3.0 km · Le Pecq 3.0 km · Saint-Germain-en-Laye 4.0 km · Houilles 4.0 km · Maisons-Laffitte 5.0 km · Rueil-Malmaison 5.0 km · Nanterre 5.0 km

France travel facts

Travel advisory
Level 2
Exercise Increased Caution
Power plugs
Type C / E
230 V · 50 Hz
Prices
≈ 77% of US
price level, 2025
GDP per capita
$48,986
2025
Happiness
6.6 / 10
World Happiness, 2025
Safe drinking water
100%
of population, 2024
Homicide rate
1.3
per 100k, 2023
Road deaths
5.1
per 100k/yr, 2019
Income group
High
World Bank
English
Moderate
EF EPI 539
Religion
Roman Catholic 47%none 33%Muslim 4%Protestant 2%

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 Montesson (48.9092°, 2.1375°, elevation 37 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. Monthly air-quality (PM2.5) seasonality is from the CAMS EAC4 reanalysis (Copernicus Atmosphere Monitoring Service), scaled to the WHO annual mean where available. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).