Oconomowoc weather in September

In September, Oconomowoc sees average daytime highs of 72°F and overnight lows near 54°F, with 2.9 in of rain across 8.5 wet days and about 12.3 hours of daylight. It is the 4th-warmest and 6th-wettest month of the year here.

Highs ease over the month, from about 77°F in the first days to 67°F by the end. The sky is clear or mostly clear about 40% of the time in September, and the air most often feels dry.

Daylight stretches from about 13 hours at the start of September to 11 h 36 min by month's end. Set against the rest of the year, September is Oconomowoc's 1st-clearest and 9th-windiest month. For the whole year in context, see Oconomowoc's year-round climate.

Daytime high
72°
4th warmest
Overnight low
54°
9th coldest
Rainfall
2.9 in
8.5 wet days
Daylight
12 h 18 min
5:40 AM – 5:57 PM
Cloud cover
52%
1st clearest
Wind
7 mph
9th windiest
Solar energy
4.27 kWh/m²
Travel score
6.9
out of 10

Oconomowoc is city in Waukesha County, Wisconsin, United States.

Founded
1837

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 77°F in the first days to 67°F by the end.

A typical September day in Oconomowoc reaches about 72°F in the afternoon and slips back to 54°F overnight — a 18°F spread between the day's warmth and the night's chill. On most days the high lands between 61°F and 83°F. Set against its neighbours, September runs about 7°F cooler than August and about 13°F warmer than October.

40°60°80°151015202530
Avg high (°F)Avg low (°F)
17759
27759
37758
47658
57658
67657
77557
87557
97556
107456
117455
127455
137355
147354
157354
167254
177253
187153
197152
207052
217051
227051
236951
246950
256850
266849
276749
286749
296748
306648

How September really feels in Oconomowoc

Once humidity and wind are folded in, September averages 0 days that feel above 90°F and 0 that feel at or below 32°F — the comfort signal a plain temperature reading hides.

Days feeling ≥ 90°F
0
heat index over the day's high
Days feeling ≤ 32°F
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.

Oconomowoc 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 (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan28° / 14°1.78.26.89.20.0
Feb32° / 17°1.775.710.20.0
Mar44° / 27°2.39.44.111.60.9
Apr56° / 38°3.911.91.613.13.7
May68° / 49°3.811.9014.45.9
Jun78° / 59°3.811.4015.16.5
Jul81° / 64°3.49.7014.96.5
Aug79° / 62°3.510.3013.86.7
Sep72° / 54°2.98.5012.36.9
Oct59° / 42°2.890.310.84.7
Nov45° / 31°2.18.229.51.0
Dec33° / 20°2.07.75.18.90.0

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 40% of the time in September, the clearest month of the year.

Beyond those clear spells, partly cloudy skies cover about 15% of September, with mostly cloudy or overcast conditions the remaining 45%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
15743
25842
35842
45842
55842
65842
75842
85743
95743
105644
115644
125644
135545
145545
155545
165446
175446
185446
195446
205446
215446
225446
235347
245347
255248
265248
275149
285248
295248
305248

Chance of precipitation in September

Any precipitation

Oconomowoc gets around 2.9 in of rain over 8.5 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 29% and peaks near 31% on the wettest days.

0%10%20%30%40%151015202530
Rain chance (%)
128
228
327
427
527
627
727
827
927
1028
1128
1229
1329
1430
1530
1631
1731
1831
1931
2031
2131
2231
2331
2431
2531
2631
2731
2830
2930
3029

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 57% of days. Sticky, muggy-or-worse air turns up on roughly 10% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
1312523174
2332522164
3352522153
4372421143
5392421142
6412321132
7432320122
8452220122
9462219111
10482219111
11502118101
12512117101
13522017101
1454201691
1556201590
1658191580
1759191480
1862181370
1962181370
2065171260
2167161160
2270151050
2370151050
247314940
257413940
267612840
277811830
287811830
298010730
30829720

Wind in September

Winds average 7 mph in September.

Across September, daily wind ranges from about 6 mph on the calmest days to 8 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202530
Wind speed (mph)Feels
16calm
26calm
37calm
47calm
57calm
67calm
77calm
87calm
97calm
107calm
117calm
127calm
137calm
147calm
157calm
167calm
177calm
187calm
197calm
207calm
217calm
227calm
237calm
247light breeze
258light breeze
268light breeze
278light breeze
288light breeze
298light breeze
308light breeze

Sunrise & sunset in September

DaylightNight

Daylight runs from about 13 hours at the start of September to 11 h 36 min by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 84 minutes over September. Sunrise moves from 5:23 AM to 5:56 AM, and sunset from 6:25 PM to 5:31 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.05:236:25
213.05:246:23
312.95:256:21
412.95:266:19
512.85:276:17
612.85:286:16
712.75:296:14
812.75:316:12
912.65:326:10
1012.65:336:08
1112.55:346:06
1212.55:356:05
1312.45:366:03
1412.45:376:01
1512.35:395:59
1612.35:405:57
1712.25:415:55
1812.25:425:53
1912.15:435:51
2012.15:445:49
2112.05:455:48
2212.05:465:46
2311.95:485:44
2411.95:495:42
2511.85:505:40
2611.85:515:38
2711.75:525:36
2811.75:535:35
2911.65:555:33
3011.65:565:31

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.27 kWh/m².

For context, solar energy here swings from a low near 1.55 kWh/m² to a high of 6.29 kWh/m² in June across the year — September's 4.27 kWh/m² falls in the middle.

024151015202530
Solar energy (kWh/m²)Level
14.8Bright
24.8Bright
34.8Bright
44.7Bright
54.7Bright
64.7Bright
74.6Bright
84.6Bright
94.5Bright
104.5Bright
114.4Bright
124.4Bright
134.3Bright
144.3Bright
154.3Bright
164.2Bright
174.2Bright
184.1Bright
194.1Bright
204.0Bright
214.0Bright
224.0Moderate
233.9Moderate
243.9Moderate
253.9Moderate
263.8Moderate
273.8Moderate
283.7Moderate
293.7Moderate
303.7Moderate
Planning a trip in September

Is September a good time to visit Oconomowoc?

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

6.9
Sightseeing
1st-best month of the year
4.9
Beach & pool
4th-best month of the year

September is a reasonable time to visit Oconomowoc for sightseeing.

What to pack for Oconomowoc in September

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

In September, Oconomowoc sees daytime highs around 72°F and nights near 54°F. Worth packing: light clothes and rain gear. About 9 days see rain.

light clothesrain gear

Sea temperature near Oconomowoc in September

The nearest coast averages about 66°F in September — the other half of the beach question. The full-year curve and swim-comfort zones are below.

The sea at the nearest coast (about 32 mi away) is warmest in August at about 70°F and coldest in March near 36°F.

It's comfortable for a long swim from Jul 29 to Aug 30 — about 1.1 months when the water holds above 68°F.

30°40°50°60°70°JanFebMarAprMayJunJulAugSepOctNovDecbracingcoolrefreshingwarm
Sea temperature (°F)Comfort
Jan38Bracing
Feb36Bracing
Mar36Bracing
Apr38Bracing
May42Bracing
Jun54Bracing
Jul67Cool
Aug70Refreshing
Sep66Cool
Oct56Bracing
Nov46Bracing
Dec41Bracing

UV index in Oconomowoc in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 6 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Oconomowoc peaks around June 20 at about 9 (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 highHighModerateLowJun 20UV 9Jan 1UV 1
UV index (midday)Level
Jan1Low
Feb2Moderate
Mar4Moderate
Apr6High
May8Very high
Jun9Very high
Jul8Very high
Aug8Very high
Sep6High
Oct3Moderate
Nov2Low
Dec1Low

Air quality in Oconomowoc 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 Oconomowoc is worst in July — around 17 µg/m³ PM2.5 (moderate), about 1.9× the cleanest month (October, 9 µg/m³).

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

01020JanFebMarAprMayJunJulAugSepOctNovDecModerateGoodJul 1616 µg/m³Oct 239 µg/m³
PM2.5 (µg/m³)Level
Jan12Good
Feb14Moderate
Mar15Moderate
Apr13Moderate
May15Moderate
Jun16Moderate
Jul17Moderate
Aug15Moderate
Sep12Moderate
Oct9Good
Nov9Good
Dec10Good
Location & terrain

Where is Oconomowoc?

Oconomowoc sits at 43.1°N, 88.5°W, 863 ft above sea level, in United States. The nearest listed city is Watertown, 13 mi away.

Topography around Oconomowoc

How much the land rises and falls, and what covers it, within 2, 10 and 50 miles of Oconomowoc.

Within 2 miles, the terrain around Oconomowoc has only modest variations in elevation — a maximum elevation change of 148 ft around an average of 879 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 440 ft; within 50 miles, significant variations in elevation — a maximum elevation change of 846 ft.

The land around Oconomowoc is covered by trees (35%), grassland (23%) and artificial surfaces (20%) within 2 miles, trees (36%), cropland (31%) and grassland (24%) within 10 miles, and cropland (44%) and trees (23%) within 50 miles.

2 miles
148 ft
10 miles
440 ft
50 miles
846 ft
treesgrasslandcroplandartificial surfaceswaterwetland
September weather nearby: Watertown 13 mi · Waukesha 15 mi · Menomonee Falls 20 mi · Brookfield 20 mi · Germantown 21 mi · New Berlin 22 mi · Muskego 23 mi · Mequon 25 mi

United States travel facts

Power plugs
Type A / B
120 V · 60 Hz
Prices
≈ 100% of US
price level, 2025
GDP per capita
$90,027
2025
Happiness
6.8 / 10
World Happiness, 2025
Safe drinking water
98%
of population, 2024
Homicide rate
5.8
per 100k, 2023
Road deaths
12.7
per 100k/yr, 2019
Income group
High
World Bank
Religion
Protestant 47%unaffiliated 23%Roman Catholic 21%Jewish 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 Oconomowoc (43.1117°, -88.4993°, elevation 863 ft), 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. Sea temperatures are the NOAA OISST v2.1 1991–2020 monthly climatology (public domain), sampled at the nearest ocean point. 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).