Ann Arbor weather in September

In September, Ann Arbor sees average daytime highs of 73°F and overnight lows near 54°F, with 2.7 in of rain across 8.6 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 68°F by the end. The sky is clear or mostly clear about 36% 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 Ann Arbor's 1st-clearest and 9th-windiest month. For the whole year in context, see Ann Arbor's year-round climate.

Daytime high
73°
4th warmest
Overnight low
54°
9th coldest
Rainfall
2.7 in
8.6 wet days
Daylight
12 h 18 min
6:21 AM – 6:38 PM
Cloud cover
55%
1st clearest
Wind
7 mph
9th windiest
Solar energy
4.32 kWh/m²
Travel score
6.9
out of 10

Ann Arbor is county seat of Washtenaw County, Michigan, United States.

Density
1,561/km²
people per km²
Founded
1824

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 68°F by the end.

A typical September day in Ann Arbor reaches about 73°F in the afternoon and slips back to 54°F overnight — a 19°F spread between the day's warmth and the night's chill. On most days the high lands between 62°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)
17859
27759
37758
47758
57758
67657
77657
87657
97556
107556
117556
127455
137455
147454
157354
167354
177353
187253
197252
207152
217151
227151
237051
247050
256950
266950
276849
286849
296848
306748

How September really feels in Ann Arbor

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.

Ann Arbor 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
Jan31° / 19°2.49.76.19.30.0
Feb34° / 20°2.18.25.610.30.0
Mar45° / 28°2.59.73.611.61.0
Apr57° / 39°3.611.81.313.13.9
May68° / 49°3.912.5014.45.9
Jun78° / 59°3.710.50156.6
Jul82° / 63°3.310.8014.86.3
Aug80° / 61°3.310.3013.76.6
Sep73° / 54°2.78.6012.36.9
Oct60° / 43°2.79.30.210.84.9
Nov47° / 33°2.691.99.61.5
Dec36° / 25°2.394.690.0

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 36% 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 48%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
15743
25743
35743
45743
55743
65743
75743
85545
95545
105545
115446
125446
135347
145347
155149
165149
175149
185050
195050
205050
214951
224951
234951
244852
254852
264852
274852
284951
294951
304951

Chance of precipitation in September

Any precipitation

Ann Arbor gets around 2.7 in of rain over 8.6 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
328
429
529
629
729
829
928
1029
1129
1229
1329
1429
1529
1629
1728
1828
1928
2028
2129
2229
2329
2430
2530
2630
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 56% of days. Sticky, muggy-or-worse air turns up on roughly 9% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
1302722192
2312722182
3332721172
4352721162
5372720142
6392720132
7412619121
8432619111
9442618111
10462518101
1148251791
1249241791
1351241681
1452231681
1556221570
1658211470
1758211470
1861201360
1963191260
2064181260
2166181150
2268171050
237016950
247215940
257315840
267414840
277613830
287713730
297812730
307812730

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
36calm
46calm
57calm
67calm
77calm
87calm
97calm
107calm
117calm
127calm
137calm
147calm
157calm
167calm
177calm
187calm
197calm
207calm
217calm
227calm
237calm
247calm
257calm
267calm
277light 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 6:05 AM to 6:36 AM, and sunset from 7:05 PM to 6:12 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.06:057:05
213.06:067:03
312.96:077:01
412.96:086:59
512.86:096:58
612.86:106:56
712.76:116:54
812.76:126:52
912.66:136:51
1012.66:146:49
1112.56:156:47
1212.56:176:45
1312.46:186:43
1412.46:196:41
1512.36:206:40
1612.36:216:38
1712.26:226:36
1812.26:236:34
1912.16:246:32
2012.16:256:30
2112.06:266:29
2212.06:276:27
2311.96:296:25
2411.96:306:23
2511.86:316:21
2611.86:326:19
2711.76:336:18
2811.76:346:16
2911.66:356:14
3011.66:366:12

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.32 kWh/m².

For context, solar energy here swings from a low near 1.45 kWh/m² to a high of 6.3 kWh/m² in June across the year — September's 4.32 kWh/m² falls in the middle.

024151015202530
Solar energy (kWh/m²)Level
14.8Bright
24.8Bright
34.8Bright
44.8Bright
54.7Bright
64.7Bright
74.6Bright
84.6Bright
94.6Bright
104.5Bright
114.5Bright
124.4Bright
134.4Bright
144.3Bright
154.3Bright
164.3Bright
174.2Bright
184.2Bright
194.2Bright
204.1Bright
214.1Bright
224.0Bright
234.0Bright
244.0Moderate
253.9Moderate
263.9Moderate
273.8Moderate
283.8Moderate
293.7Moderate
303.7Moderate
Planning a trip in September

Is September a good time to visit Ann Arbor?

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
5.1
Beach & pool
4th-best month of the year

September is a reasonable time to visit Ann Arbor for sightseeing.

What to pack for Ann Arbor in September

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

In September, Ann Arbor sees daytime highs around 73°F and nights near 54°F. Worth packing: light clothes and rain gear. About 9 days see rain.

light clothesrain gear

Sea temperature near Ann Arbor in September

The nearest coast averages about 70°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 34 mi away) is warmest in August at about 75°F and coldest in February near 33°F.

It's comfortable for a long swim from Jun 20 to Sep 20 — about 3.1 months when the water holds above 68°F.

30°40°50°60°70°80°JanFebMarAprMayJunJulAugSepOctNovDecbracingcoolrefreshingwarmtropicalcomfortable to swim
Sea temperature (°F)Comfort
Jan34Bracing
Feb33Bracing
Mar36Bracing
Apr44Bracing
May56Bracing
Jun67Cool
Jul75Refreshing
Aug75Warm
Sep70Refreshing
Oct58Bracing
Nov46Bracing
Dec38Bracing

UV index in Ann Arbor 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 Ann Arbor peaks around June 20 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 20 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 9Dec 20UV 1
UV index (midday)Level
Jan2Low
Feb2Moderate
Mar4Moderate
Apr6High
May7High
Jun9Very high
Jul9Very high
Aug7High
Sep6High
Oct3Moderate
Nov2Moderate
Dec1Low

Air quality in Ann Arbor 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 Ann Arbor is worst in July — around 16 µg/m³ PM2.5 (moderate), about 1.9× the cleanest month (October, 8 µg/m³).

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

01020JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodJul 1116 µg/m³Oct 238 µg/m³
PM2.5 (µg/m³)Level
Jan10Good
Feb13Moderate
Mar14Moderate
Apr13Moderate
May15Moderate
Jun16Moderate
Jul16Moderate
Aug15Moderate
Sep12Good
Oct8Good
Nov9Good
Dec9Good
Location & terrain

Where is Ann Arbor?

Ann Arbor sits at 42.3°N, 83.7°W, 883 ft above sea level, in United States. The nearest listed city is Ypsilanti, 6.8 mi away.

Topography around Ann Arbor

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

Within 2 miles, the terrain around Ann Arbor has only modest variations in elevation — a maximum elevation change of 295 ft around an average of 883 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 436 ft; within 50 miles, significant variations in elevation — a maximum elevation change of 945 ft.

The land around Ann Arbor is covered by trees (60%) and artificial surfaces (30%) within 2 miles, trees (49%) and grassland (24%) within 10 miles, and trees (40%) and cropland (29%) within 50 miles.

2 miles
295 ft
10 miles
436 ft
50 miles
945 ft
treesgrasslandcroplandartificial surfaceswater
September weather nearby: Ypsilanti 6.8 mi · Canton 14 mi · Westland 17 mi · Romulus 18 mi · Wayne 18 mi · Novi 19 mi · Livonia 21 mi · Garden City 21 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 Ann Arbor (42.2776°, -83.7409°, elevation 883 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).