Johnston weather in September

In September, Johnston sees average daytime highs of 75°F and overnight lows near 55°F, with 3.4 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 80°F in the first days to 71°F by the end. The sky is clear or mostly clear about 47% 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 Johnston's 1st-clearest and 9th-windiest month. For the whole year in context, see Johnston's year-round climate.

Daytime high
75°
4th warmest
Overnight low
55°
9th coldest
Rainfall
3.4 in
8.6 wet days
Daylight
12 h 18 min
6:01 AM – 6:17 PM
Cloud cover
45%
1st clearest
Wind
9 mph
9th windiest
Solar energy
4.63 kWh/m²
Travel score
7.2
out of 10

Johnston is city in Polk County, Iowa, United States.

Density
440/km²
people per km²
Founded
1969

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 80°F in the first days to 71°F by the end.

A typical September day in Johnston reaches about 75°F in the afternoon and slips back to 55°F overnight — a 21°F spread between the day's warmth and the night's chill. On most days the high lands between 64°F and 86°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)
18060
28060
38060
48059
57959
67959
77858
87858
97857
107757
117756
127656
137656
147655
157555
167555
177554
187454
197453
207353
217353
227352
237252
247251
257251
267150
277150
287150
297049
307049

How September really feels in Johnston

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.

Johnston 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
Jan29° / 13°1.26.24.99.30.0
Feb34° / 17°1.46.54.810.30.0
Mar48° / 29°2.68.82.811.71.7
Apr61° / 40°4.311.1113.14.7
May71° / 52°5.513.70.114.36.0
Jun80° / 62°5.012.10156.1
Jul84° / 66°3.79.5014.75.8
Aug82° / 63°3.99.2013.76.6
Sep75° / 55°3.48.6012.37.2
Oct62° / 42°2.980.410.95.7
Nov47° / 30°2.16.51.39.61.8
Dec35° / 19°1.664.190.0

Cloud cover in September

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 47% 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 38%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
16634
26634
36634
46634
56535
66436
76436
86337
96337
106238
116238
126238
136040
146040
155941
165941
175941
185941
195941
205941
216040
226040
236040
246139
256139
266139
276139
286139
296139
306139

Chance of precipitation in September

Any precipitation

Johnston gets around 3.4 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
527
627
727
828
929
1029
1130
1230
1331
1432
1532
1632
1732
1832
1932
2032
2131
2231
2330
2429
2529
2628
2728
2828
2927
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 (%)
1222324247
2242324237
3262423216
4282423196
5302423185
6322422175
7342422164
8362421154
9382321144
10402320143
11422320133
12432319133
13452318122
14472217122
15492217112
16502216111
17532115101
18542114101
19552113101
2058201291
2159201191
2262191081
236419971
246618970
256917860
267016860
277216750
287315750
297614640
307713640

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
128light 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 5:45 AM to 6:16 AM, and sunset from 6:44 PM to 5:52 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
113.05:456:44
212.95:466:42
312.95:476:41
412.85:486:39
512.85:496:37
612.75:506:35
712.75:516:33
812.75:526:32
912.65:536:30
1012.65:556:28
1112.55:566:26
1212.55:576:25
1312.45:586:23
1412.45:596:21
1512.36:006:19
1612.36:016:17
1712.26:026:16
1812.26:036:14
1912.16:046:12
2012.16:056:10
2112.06:066:08
2212.06:076:07
2311.96:086:05
2411.96:096:03
2511.86:106:01
2611.86:125:59
2711.76:135:58
2811.76:145:56
2911.76:155:54
3011.66:165:52

Solar energy in September

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in September, about 4.63 kWh/m².

For context, solar energy here swings from a low near 1.8 kWh/m² to a high of 6.47 kWh/m² in July across the year — September's 4.63 kWh/m² falls in the middle.

0246151015202530
Solar energy (kWh/m²)Level
15.3Bright
25.2Bright
35.2Bright
45.1Bright
55.1Bright
65.0Bright
75.0Bright
85.0Bright
94.9Bright
104.8Bright
114.8Bright
124.8Bright
134.7Bright
144.6Bright
154.6Bright
164.5Bright
174.5Bright
184.5Bright
194.4Bright
204.4Bright
214.3Bright
224.3Bright
234.2Bright
244.2Bright
254.2Bright
264.1Bright
274.1Bright
284.0Bright
294.0Bright
304.0Moderate
Planning a trip in September

Is September a good time to visit Johnston?

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
5.9
Beach & pool
4th-best month of the year

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

What to pack for Johnston in September

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

In September, Johnston sees daytime highs around 75°F and nights near 55°F. Worth packing: light clothes, rain gear and sun protection. About 9 days see rain.

light clothesrain gearsun protection

UV index in Johnston 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 Johnston peaks around June 20 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 21 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 20UV 9Dec 21UV 2
UV index (midday)Level
Jan2Low
Feb3Moderate
Mar4Moderate
Apr6High
May7High
Jun9Very high
Jul9Very high
Aug7Very high
Sep6High
Oct4Moderate
Nov3Moderate
Dec2Low

Air quality in Johnston 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 Johnston 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 2016 µg/m³Oct 217 µg/m³
PM2.5 (µg/m³)Level
Jan13Moderate
Feb15Moderate
Mar14Moderate
Apr11Good
May11Good
Jun12Moderate
Jul16Moderate
Aug14Moderate
Sep12Good
Oct7Good
Nov9Good
Dec10Good
Location & terrain

Where is Johnston?

Johnston sits at 41.7°N, 93.7°W, 830 ft above sea level, in United States. The nearest listed city is Urbandale, 3.1 mi away.

Topography around Johnston

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

Within 2 miles, the terrain around Johnston has only modest variations in elevation — a maximum elevation change of 217 ft around an average of 846 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 305 ft; within 50 miles, only modest variations in elevation — a maximum elevation change of 787 ft.

The land around Johnston is covered by trees (40%) and grassland (26%) within 2 miles, trees (29%), cropland (25%) and grassland (22%) within 10 miles, and cropland (65%) within 50 miles.

2 miles
217 ft
10 miles
305 ft
50 miles
787 ft
treesgrasslandcroplandartificial surfacesbare terrainwater
September weather nearby: Urbandale 3.1 mi · Clive 5.0 mi · Ankeny 6.2 mi · West Des Moines 6.8 mi · Des Moines 6.8 mi · Waukee 11 mi · Altoona 12 mi · Indianola 23 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 Johnston (41.673°, -93.6977°, elevation 830 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).