Iowa City weather in September

In September, Iowa City sees average daytime highs of 75°F and overnight lows near 55°F, with 3.9 in of rain across 8.2 wet days and about 12.3 hours of daylight. It is the 4th-warmest and 4th-wettest month of the year here.

Highs ease over the month, from about 79°F in the first days to 70°F by the end. The sky is clear or mostly clear about 46% 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 Iowa City's 1st-clearest and 9th-windiest month. For the whole year in context, see Iowa City's year-round climate.

Daytime high
75°
4th warmest
Overnight low
55°
9th coldest
Rainfall
3.9 in
8.2 wet days
Daylight
12 h 18 min
5:52 AM – 6:09 PM
Cloud cover
47%
1st clearest
Wind
8 mph
9th windiest
Solar energy
4.56 kWh/m²
Travel score
7.2
out of 10

Iowa City is city in Johnson County, Iowa, United States.

Density
1,093/km²
people per km²
Founded
1839

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 79°F in the first days to 70°F by the end.

A typical September day in Iowa City reaches about 75°F in the afternoon and slips back to 55°F overnight — a 20°F spread between the day's warmth and the night's chill. On most days the high lands between 64°F and 85°F. Set against its neighbours, September runs about 6°F cooler than August and about 13°F warmer than October.

40°60°80°151015202530
Avg high (°F)Avg low (°F)
18060
27960
37960
47959
57859
67859
77858
87758
97757
107757
117657
127656
137656
147555
157555
167455
177454
187454
197353
207353
217353
227252
237252
247151
257151
267151
277050
287050
297049
306949

How September really feels in Iowa City

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.

Iowa City weather by month

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

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan29° / 14°1.57.15.39.30.0
Feb33° / 18°1.86.44.210.30.0
Mar47° / 29°2.79.22.811.71.6
Apr60° / 41°4.411.80.813.14.5
May71° / 52°4.913.4014.36.0
Jun80° / 62°5.111.70156.3
Jul83° / 65°3.79.6014.76.1
Aug81° / 63°3.89.1013.76.8
Sep75° / 55°3.98.2012.37.2
Oct62° / 43°2.98.60.210.95.5
Nov47° / 31°2.37.71.59.71.7
Dec34° / 20°1.96.94.590.0

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 46% of the time in September, the clearest month of the year.

Beyond those clear spells, partly cloudy skies cover about 14% of September, with mostly cloudy or overcast conditions the remaining 40%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
16436
26436
36436
46436
56436
66436
76436
86436
96337
106238
116238
126040
136040
146040
155842
165743
175743
185743
195743
205644
215644
225644
235743
245743
255743
265743
275743
285743
295842
305842

Chance of precipitation in September

Any precipitation

Iowa City gets around 3.9 in of rain over 8.2 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 28% and peaks near 30% on the wettest days.

0%10%20%30%40%151015202530
Rain chance (%)
126
226
325
425
525
625
725
826
926
1026
1127
1228
1328
1429
1530
1630
1730
1830
1930
2030
2130
2230
2330
2430
2529
2629
2729
2828
2928
3027

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 50% of days. Sticky, muggy-or-worse air turns up on roughly 14% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
1222523228
2242522218
3262522207
4282522196
5302521186
6322521175
7342520165
8372420154
9392419144
10412419143
11432318143
12442317132
13462217132
14482216132
15512115121
16522114121
17542013121
18552013111
19562012111
20591911101
2161191190
2263181090
2365171080
246717970
256816970
267015960
277314850
287314850
297513840
307613740

Wind in September

Winds average 8 mph in September.

Across September, daily wind ranges from about 7 mph on the calmest days to 9 mph at its breeziest. It stays fairly steady from day to day.

051015151015202530
Wind speed (mph)Feels
17light breeze
28light breeze
38light breeze
48light breeze
58light breeze
68light breeze
78light breeze
88light breeze
98light breeze
108light breeze
118light breeze
128light breeze
138light breeze
148light breeze
158light breeze
168light breeze
178light breeze
188light breeze
198light breeze
208light breeze
219light breeze
229light breeze
239light breeze
249light breeze
259light breeze
269light breeze
279light breeze
289light breeze
299light breeze
309light 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 5:36 AM to 6:07 AM, and sunset from 6:35 PM to 5:44 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.05:366:35
212.95:376:34
312.95:386:32
412.85:406:30
512.85:416:28
612.75:426:27
712.75:436:25
812.75:446:23
912.65:456:21
1012.65:466:19
1112.55:476:18
1212.55:486:16
1312.45:496:14
1412.45:506:12
1512.35:516:10
1612.35:526:09
1712.25:536:07
1812.25:546:05
1912.15:556:03
2012.15:566:01
2112.05:586:00
2212.05:595:58
2311.96:005:56
2411.96:015:54
2511.86:025:52
2611.86:035:51
2711.76:045:49
2811.76:055:47
2911.76:065:45
3011.66:075:44

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.56 kWh/m².

For context, solar energy here swings from a low near 1.74 kWh/m² to a high of 6.39 kWh/m² in July across the year — September's 4.56 kWh/m² falls in the middle.

0246151015202530
Solar energy (kWh/m²)Level
15.1Bright
25.1Bright
35.1Bright
45.0Bright
55.0Bright
65.0Bright
74.9Bright
84.9Bright
94.8Bright
104.8Bright
114.7Bright
124.7Bright
134.6Bright
144.6Bright
154.5Bright
164.5Bright
174.4Bright
184.4Bright
194.3Bright
204.3Bright
214.3Bright
224.2Bright
234.2Bright
244.1Bright
254.1Bright
264.1Bright
274.0Bright
284.0Moderate
294.0Moderate
303.9Moderate
Planning a trip in September

Is September a good time to visit Iowa City?

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

7.2
Sightseeing
1st-best month of the year
5.8
Beach & pool
4th-best month of the year

September is one of the better times to visit Iowa City for general sightseeing.

What to pack for Iowa City in September

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

In September, Iowa City sees daytime highs around 75°F and nights near 55°F. Worth packing: light clothes, rain gear and sun protection. About 8 days see rain.

light clothesrain gearsun protection

UV index in Iowa City 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 Iowa City peaks around June 19 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 20 at about 2 (low).

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

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highHighModerateLowJun 19UV 9Dec 20UV 2
UV index (midday)Level
Jan2Low
Feb3Moderate
Mar4Moderate
Apr6High
May8Very high
Jun9Very high
Jul9Very high
Aug8Very high
Sep6High
Oct3Moderate
Nov3Moderate
Dec2Low

Air quality in Iowa City 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 Iowa City is worst in July — around 17 µg/m³ PM2.5 (moderate), about 2.2× the cleanest month (October, 8 µg/m³).

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

01020JanFebMarAprMayJunJulAugSepOctNovDecModerateGoodModerateGoodJul 1916 µg/m³Oct 218 µg/m³
PM2.5 (µg/m³)Level
Jan12Moderate
Feb14Moderate
Mar14Moderate
Apr11Good
May13Moderate
Jun13Moderate
Jul17Moderate
Aug15Moderate
Sep12Good
Oct8Good
Nov8Good
Dec10Good
Location & terrain

Where is Iowa City?

Iowa City sits at 41.7°N, 91.5°W, 669 ft above sea level, in United States. The nearest listed city is Coralville, 3.1 mi away.

Topography around Iowa City

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

Within 2 miles, the terrain around Iowa City has only modest variations in elevation — a maximum elevation change of 223 ft around an average of 715 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 384 ft; within 50 miles, only modest variations in elevation — a maximum elevation change of 646 ft.

The land around Iowa City is covered by trees (50%) and artificial surfaces (31%) within 2 miles, cropland (57%) within 10 miles, and cropland (72%) within 50 miles.

2 miles
223 ft
10 miles
384 ft
50 miles
646 ft
treesgrasslandcroplandartificial surfaceswater
September weather nearby: Coralville 3.1 mi · North Liberty 6.8 mi · Cedar Rapids 25 mi · Marion 26 mi · Muscatine 30 mi · Davenport 50 mi · Rock Island 50 mi · Bettendorf 53 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 Iowa City (41.6611°, -91.5302°, 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. 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).