Waterloo weather in September

In September, Waterloo sees average daytime highs of 73°F and overnight lows near 53°F, with 3.7 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 78°F in the first days to 69°F by the end. The sky is clear or mostly clear about 45% 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 Waterloo's 1st-clearest and 9th-windiest month. For the whole year in context, see Waterloo's year-round climate.

Daytime high
73°
4th warmest
Overnight low
53°
9th coldest
Rainfall
3.7 in
8.6 wet days
Daylight
12 h 18 min
5:55 AM – 6:12 PM
Cloud cover
48%
1st clearest
Wind
9 mph
9th windiest
Solar energy
4.48 kWh/m²
Travel score
7.1
out of 10

Waterloo is city in Black Hawk County, Iowa, United States.

Density
418/km²
people per km²
Founded
1868

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 78°F in the first days to 69°F by the end.

A typical September day in Waterloo reaches about 73°F in the afternoon and slips back to 53°F overnight — a 20°F spread between the day's warmth and the night's chill. On most days the high lands between 62°F and 84°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)
17859
27858
37858
47758
57757
67757
77657
87656
97656
107555
117555
127555
137454
147454
157454
167353
177353
187352
197252
207252
217151
227151
237150
247050
257049
266949
276949
286948
296848
306847

How September really feels in Waterloo

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.

Waterloo 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
Jan26° / 11°1.46.85.69.20.0
Feb31° / 15°1.46.54.810.30.0
Mar45° / 27°2.593.411.61.1
Apr59° / 39°4.311.21.113.14.3
May70° / 51°5.0130.114.46.0
Jun79° / 61°5.112.4015.16.3
Jul82° / 64°4.210.3014.86.5
Aug80° / 61°3.99.5013.76.8
Sep73° / 53°3.78.6012.37.1
Oct60° / 41°2.88.30.410.85.2
Nov45° / 29°2.17.22.19.61.2
Dec32° / 18°1.76.95.18.90.0

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 45% of the time in September, the clearest month of the year.

Beyond those clear spells, partly cloudy skies cover about 13% of September, with mostly cloudy or overcast conditions the remaining 42%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
16337
26337
36436
46337
56337
66337
76337
86238
96139
106040
115941
125941
135842
145743
155644
165545
175545
185446
195446
205446
215446
225446
235545
245545
255545
265545
275545
285644
295644
305743

Chance of precipitation in September

Any precipitation

Waterloo gets around 3.7 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 32% on the wettest days.

0%10%20%30%40%151015202530
Rain chance (%)
126
226
326
426
526
627
727
827
928
1029
1129
1230
1331
1431
1532
1632
1732
1832
1932
2032
2131
2231
2331
2430
2530
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 55% of days. Sticky, muggy-or-worse air turns up on roughly 12% of them.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)
1272521207
2292521196
3312520176
4342520165
5362519155
6392519144
7412418134
8432418123
9452318123
10472217112
11492217112
12502116112
13522116101
14542015101
15552014101
1656201491
1759191390
1860191290
1962181280
2063181180
2166171070
226717970
236916960
247115860
257215850
267414750
277613740
287613740
297912630
308011630

Wind in September

Winds average 9 mph in September.

Across September, daily wind ranges from about 8 mph on the calmest days to 9 mph at its breeziest. It stays fairly steady from day to day.

051015151015202530
Wind speed (mph)Feels
18light breeze
28light breeze
38light breeze
48light breeze
58light breeze
68light breeze
78light breeze
88light breeze
98light breeze
108light breeze
118light breeze
129light breeze
139light breeze
149light breeze
159light breeze
169light breeze
179light breeze
189light breeze
199light breeze
209light 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 5:39 AM to 6:11 AM, and sunset from 6:39 PM to 5:47 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.05:396:39
213.05:406:38
312.95:416:36
412.95:426:34
512.85:436:32
612.85:446:30
712.75:456:29
812.75:466:27
912.65:486:25
1012.65:496:23
1112.55:506:21
1212.55:516:20
1312.45:526:18
1412.45:536:16
1512.35:546:14
1612.35:556:12
1712.25:566:10
1812.25:576:08
1912.15:596:07
2012.16:006:05
2112.06:016:03
2212.06:026:01
2311.96:035:59
2411.96:045:57
2511.86:055:56
2611.86:065:54
2711.76:075:52
2811.76:095:50
2911.66:105:48
3011.66:115:47

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.48 kWh/m².

For context, solar energy here swings from a low near 1.7 kWh/m² to a high of 6.37 kWh/m² in July across the year — September's 4.48 kWh/m² falls in the middle.

0246151015202530
Solar energy (kWh/m²)Level
15.1Bright
25.1Bright
35.0Bright
45.0Bright
55.0Bright
64.9Bright
74.9Bright
84.8Bright
94.8Bright
104.7Bright
114.7Bright
124.6Bright
134.5Bright
144.5Bright
154.4Bright
164.4Bright
174.3Bright
184.3Bright
194.2Bright
204.2Bright
214.1Bright
224.1Bright
234.1Bright
244.0Bright
254.0Moderate
263.9Moderate
273.9Moderate
283.9Moderate
293.8Moderate
303.8Moderate
Planning a trip in September

Is September a good time to visit Waterloo?

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

7.1
Sightseeing
1st-best month of the year
5.3
Beach & pool
4th-best month of the year

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

What to pack for Waterloo in September

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

In September, Waterloo sees daytime highs around 73°F and nights near 53°F. Worth packing: light clothes and rain gear. About 9 days see rain.

light clothesrain gear

UV index in Waterloo 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 Waterloo peaks around June 18 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near January 1 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 18UV 9Jan 1UV 2
UV index (midday)Level
Jan2Low
Feb3Moderate
Mar4Moderate
Apr6High
May7Very high
Jun9Very high
Jul8Very high
Aug7Very high
Sep6High
Oct3Moderate
Nov2Moderate
Dec2Low

Air quality in Waterloo 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 Waterloo is worst in July — around 16 µg/m³ PM2.5 (moderate), about 2.2× the cleanest month (October, 7 µg/m³).

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

01020JanFebMarAprMayJunJulAugSepOctNovDecModerateGoodModerateGoodJul 1916 µg/m³Oct 217 µg/m³
PM2.5 (µg/m³)Level
Jan12Moderate
Feb15Moderate
Mar14Moderate
Apr11Good
May12Good
Jun13Moderate
Jul16Moderate
Aug15Moderate
Sep12Good
Oct7Good
Nov8Good
Dec10Good
Location & terrain

Where is Waterloo?

Waterloo sits at 42.5°N, 92.3°W, 856 ft above sea level, in United States. The nearest listed city is Cedar Falls, 5.6 mi away.

Topography around Waterloo

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

Within 2 miles, the terrain around Waterloo has only modest variations in elevation — a maximum elevation change of 151 ft around an average of 873 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 243 ft; within 50 miles, only modest variations in elevation — a maximum elevation change of 620 ft.

The land around Waterloo is covered by trees (39%) and artificial surfaces (39%) within 2 miles, cropland (64%) within 10 miles, and cropland (81%) within 50 miles.

2 miles
151 ft
10 miles
243 ft
50 miles
620 ft
treesgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: Cedar Falls 5.6 mi · Marshalltown 42 mi · Cedar Rapids 49 mi · Marion 50 mi · Mason City 63 mi · North Liberty 64 mi · Newton 66 mi · Coralville 68 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 Waterloo (42.4928°, -92.343°, elevation 856 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).