Mequon weather in September

In September, Mequon sees average daytime highs of 70°F and overnight lows near 57°F, with 3.0 in of rain across 8.9 wet days and about 12.3 hours of daylight. It is the 4th-warmest and 7th-wettest month of the year here.

Highs ease over the month, from about 75°F in the first days to 65°F by the end. The sky is clear or mostly clear about 38% 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 Mequon's 1st-clearest and 8th-windiest month. For the whole year in context, see Mequon's year-round climate.

Daytime high
70°
4th warmest
Overnight low
57°
9th coldest
Rainfall
3.0 in
8.9 wet days
Daylight
12 h 18 min
5:38 AM – 5:55 PM
Cloud cover
52%
1st clearest
Wind
9 mph
8th windiest
Solar energy
4.29 kWh/m²
Travel score
6.7
out of 10

Mequon is fourth-class city in Ozaukee County, Wisconsin, United States.

Density
183/km²
people per km²
Founded
1957

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 75°F in the first days to 65°F by the end.

A typical September day in Mequon reaches about 70°F in the afternoon and slips back to 57°F overnight — a 13°F spread between the day's warmth and the night's chill. On most days the high lands between 61°F and 79°F. Set against its neighbours, September runs about 7°F cooler than August and about 12°F warmer than October.

40°50°60°70°80°151015202530
Avg high (°F)Avg low (°F)
17562
27562
37562
47462
57461
67461
77360
87360
97360
107259
117259
127259
137158
147158
157158
167057
177057
186956
196956
206956
216855
226855
236755
246754
256754
266653
276653
286552
296552
306552

How September really feels in Mequon

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.

Mequon weather by month

How September compares with the rest of the year at a glance. September is the 4th-warmest and 7th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan29° / 17°2.08.96.89.20.0
Feb31° / 19°1.86.85.610.20.0
Mar40° / 27°2.49.2411.60.2
Apr50° / 37°4.011.61.813.22.1
May60° / 47°3.611.1014.44.7
Jun71° / 59°3.510.7015.16.5
Jul78° / 65°3.19.7014.96.9
Aug77° / 65°3.510.2013.86.9
Sep70° / 57°3.08.9012.36.7
Oct58° / 46°3.19.60.210.84.3
Nov44° / 34°2.48.81.89.51.0
Dec34° / 24°2.28.15.38.90.0

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 38% of the time in September, the clearest month of the year.

Beyond those clear spells, partly cloudy skies cover about 16% of September, with mostly cloudy or overcast conditions the remaining 46%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
15743
25842
35842
45842
55842
65842
75842
85743
95743
105644
115644
125545
135545
145446
155446
165347
175347
185347
195347
205347
215248
225248
235248
245248
255149
265149
275149
285050
295050
305050

Chance of precipitation in September

Any precipitation

Mequon gets around 3.0 in of rain over 8.9 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 30% and peaks near 32% on the wettest days.

0%10%20%30%40%151015202530
Rain chance (%)
129
229
328
428
528
628
728
828
929
1029
1130
1230
1331
1431
1532
1632
1732
1832
1932
2032
2132
2232
2332
2432
2532
2632
2731
2831
2931
3030

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 53% of days. Sticky, muggy-or-worse air turns up on roughly 11% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
1272524204
2292423194
3312423184
4332422173
5352422173
6362422163
7382321152
8402321152
9422320142
10432220141
11452219131
12462219121
13482119111
14492118111
15512118100
1653211790
1755201780
1856201680
1958201570
2061191460
2162191360
2265181250
2366171250
2468171140
2570161040
267215940
277315930
287514830
297613830
307713730

Wind in September

Winds average 9 mph in September.

Across September, daily wind ranges from about 8 mph on the calmest days to 10 mph at its breeziest. It stays fairly steady from day to day.

051015151015202530
Wind speed (mph)Feels
18light breeze
29light breeze
39light breeze
49light breeze
59light breeze
69light breeze
79light breeze
89light breeze
99light breeze
109light breeze
119light breeze
129light breeze
139light breeze
149light breeze
159light breeze
169light breeze
179light breeze
1810light breeze
1910light breeze
2010light breeze
2110light breeze
2210light breeze
2310light breeze
2410light breeze
2510light breeze
2610light breeze
2710light breeze
2810light breeze
2910light breeze
3010light 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 5:21 AM to 5:54 AM, and sunset from 6:23 PM to 5:29 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.05:216:23
213.05:226:21
312.95:236:19
412.95:246:18
512.85:256:16
612.85:266:14
712.75:286:12
812.75:296:10
912.65:306:08
1012.65:316:06
1112.55:326:05
1212.55:336:03
1312.45:346:01
1412.45:355:59
1512.35:375:57
1612.35:385:55
1712.25:395:53
1812.25:405:51
1912.15:415:49
2012.15:425:48
2112.05:435:46
2212.05:455:44
2311.95:465:42
2411.95:475:40
2511.85:485:38
2611.85:495:36
2711.75:505:34
2811.75:525:33
2911.65:535:31
3011.65:545:29

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.29 kWh/m².

For context, solar energy here swings from a low near 1.47 kWh/m² to a high of 6.43 kWh/m² in June across the year — September's 4.29 kWh/m² falls in the middle.

024151015202530
Solar energy (kWh/m²)Level
14.9Bright
24.9Bright
34.8Bright
44.8Bright
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
204.1Bright
214.0Bright
224.0Moderate
234.0Moderate
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 Mequon?

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

6.7
Sightseeing
3rd-best month of the year
4.2
Beach & pool
4th-best month of the year

September is a reasonable time to visit Mequon for sightseeing.

What to pack for Mequon in September

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

In September, Mequon sees daytime highs around 70°F and nights near 57°F. Worth packing: rain gear. About 9 days see rain.

rain gear

Sea temperature near Mequon 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 10 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 Mequon in September

LowModerateHighVery highExtreme

Clear-sky midday UV in September peaks around 5 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Mequon 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
Aug7Very high
Sep5High
Oct3Moderate
Nov2Low
Dec1Low

Air quality in Mequon 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 Mequon is worst in June — around 16 µg/m³ PM2.5 (moderate), about 1.9× the cleanest month (November, 8 µg/m³).

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

01020JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodJun 2116 µg/m³Nov 138 µg/m³
PM2.5 (µg/m³)Level
Jan10Good
Feb12Good
Mar14Moderate
Apr13Moderate
May15Moderate
Jun16Moderate
Jul15Moderate
Aug14Moderate
Sep11Good
Oct8Good
Nov8Good
Dec9Good
Location & terrain

Where is Mequon?

Mequon sits at 43.2°N, 88.0°W, 669 ft above sea level, in United States. The nearest listed city is Germantown, 4.3 mi away.

Topography around Mequon

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

Within 2 miles, the terrain around Mequon has only modest variations in elevation — a maximum elevation change of 295 ft around an average of 764 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 587 ft; within 50 miles, significant variations in elevation — a maximum elevation change of 846 ft.

The land around Mequon is covered by trees (35%), grassland (33%) and cropland (25%) within 2 miles, trees (40%) and grassland (22%) within 10 miles, and water (38%) and cropland (27%) within 50 miles.

2 miles
295 ft
10 miles
587 ft
50 miles
846 ft
treesgrasslandcroplandartificial surfaceswater
September weather nearby: Germantown 4.3 mi · Menomonee Falls 5.0 mi · Brookfield 11 mi · Wauwatosa 12 mi · Milwaukee 14 mi · West Allis 14 mi · West Bend 16 mi · New Berlin 17 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 Mequon (43.2156°, -88.03°, elevation 669 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).