Johnston weather in August

In August, Johnston sees average daytime highs of 82°F and overnight lows near 63°F, with 3.9 in of rain across 9.2 wet days and about 13.7 hours of daylight. It is the 2nd-warmest and 4th-wettest month of the year here.

Day-to-day highs hold fairly steady near 82°F through the month. The sky is clear or mostly clear about 44% of the time in August, and the air most often feels muggy.

Daylight stretches from about 14 h 18 min at the start of August to 13 hours by month's end. Set against the rest of the year, August is Johnston's 2nd-clearest and 12th-windiest month. For the whole year in context, see Johnston's year-round climate.

Daytime high
82°
2nd warmest
Overnight low
63°
11th coldest
Rainfall
3.9 in
9.2 wet days
Daylight
13 h 42 min
5:28 AM – 7:10 PM
Cloud cover
48%
2nd clearest
Wind
7 mph
12th windiest
Solar energy
5.66 kWh/m²
Travel score
6.6
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 August

Average highAverage lowShaded bands: 10–90% of days

Day-to-day highs hold fairly steady near 82°F through the month.

A typical August day in Johnston reaches about 82°F in the afternoon and slips back to 63°F overnight — a 19°F spread between the day's warmth and the night's chill. On most days the high lands between 74°F and 90°F. Set against its neighbours, August runs about 2°F cooler than July and about 7°F warmer than September.

50°60°70°80°90°151015202531
Avg high (°F)Avg low (°F)
18365
28365
38365
48364
58364
68264
78264
88264
98264
108264
118264
128264
138263
148263
158263
168263
178263
188263
198263
208263
218263
228263
238263
248262
258262
268162
278162
288162
298162
308161
318161

How August really feels in Johnston

Once humidity and wind are folded in, August 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

August 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 August compares with the rest of the year at a glance. August is the 2nd-warmest and 4th-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 August

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 44% of the time in August.

Beyond those clear spells, partly cloudy skies cover about 18% of August, with mostly cloudy or overcast conditions the remaining 38%. Skies tend to open up as the month goes on.

0%25%50%75%100%151015202531
Clearer (%)Cloudier (%)
16238
26139
36139
46139
56139
66139
76139
86040
96040
106040
116040
126040
136040
146040
156139
166139
176139
186238
196238
206337
216337
226337
236436
246436
256535
266535
276634
286634
296634
306634
316634

Chance of precipitation in August

Any precipitation

Johnston gets around 3.9 in of rain over 9.2 wet days in August. 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%151015202531
Rain chance (%)
126
226
327
427
527
628
729
830
930
1031
1132
1232
1332
1432
1532
1632
1732
1832
1932
2032
2131
2231
2330
2429
2529
2628
2727
2827
2926
3026
3126

Humidity in August

DryComfortableHumidMuggyOppressiveMiserable

Most of August feels muggy — the stacked bands show each day's mix of comfort levels, read off the dew point.

By dew point, August lands in the muggy band about 29% of days. Sticky, muggy-or-worse air turns up on roughly 43% of them.

0%25%50%75%100%151015202531
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)Miserable (%)
16193126172
26193026172
36193026172
47193026162
57192927162
68192927162
78182927162
89182828162
99182828151
1010182728151
1110182729151
1211192729141
1311192629141
1411192630141
1511192630131
1611192530131
1711192531121
1811202531121
1911202532120
2011202532110
2111202532110
2211202532110
2312212532110
2412212532100
2512212531100
2613222531100
2714222530100
281522242990
291622242890
301823242780
312023242680

Wind in August

Winds average 7 mph in August, the calmest month.

Across August, daily wind ranges from about 7 mph on the calmest days to 8 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202531
Wind speed (mph)Feels
17calm
27calm
37calm
47calm
57calm
67calm
77calm
87calm
97calm
107calm
117calm
127calm
137calm
147calm
157calm
167calm
177calm
187calm
197calm
207calm
217calm
227calm
237calm
247light breeze
258light breeze
268light breeze
278light breeze
288light breeze
298light breeze
308light breeze
318light breeze

Sunrise & sunset in August

DaylightNight

Daylight runs from about 14 h 18 min at the start of August to 13 hours by month's end. The lit band spans sunrise to sunset each day.

Days shrink by about 78 minutes over August. Sunrise moves from 5:13 AM to 5:44 AM, and sunset from 7:29 PM to 6:46 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202531
Daylight (h)Sunrise (AM)Sunset (PM)
114.35:137:29
214.25:147:28
314.25:157:27
414.25:167:26
514.15:177:24
614.15:187:23
714.15:197:22
814.05:207:21
914.05:217:19
1013.95:227:18
1113.95:237:17
1213.95:247:15
1313.85:257:14
1413.85:267:13
1513.75:277:11
1613.75:287:10
1713.65:297:08
1813.65:307:07
1913.65:317:05
2013.55:327:04
2113.55:337:02
2213.45:347:00
2313.45:366:59
2413.35:376:57
2513.35:386:56
2613.35:396:54
2713.25:406:52
2813.25:416:51
2913.15:426:49
3013.15:436:47
3113.05:446:46

Solar energy in August

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in August, about 5.66 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 — August's 5.66 kWh/m² sits near the top of that range.

0246151015202531
Solar energy (kWh/m²)Level
16.1Intense
26.1Intense
36.1Intense
46.0Intense
56.0Bright
66.0Bright
75.9Bright
85.9Bright
95.8Bright
105.8Bright
115.8Bright
125.8Bright
135.7Bright
145.7Bright
155.7Bright
165.6Bright
175.6Bright
185.6Bright
195.6Bright
205.5Bright
215.5Bright
225.5Bright
235.5Bright
245.5Bright
255.4Bright
265.4Bright
275.4Bright
285.4Bright
295.3Bright
305.3Bright
315.3Bright
Planning a trip in August

Is August a good time to visit Johnston?

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

6.6
Sightseeing
2nd-best month of the year
7.1
Beach & pool
2nd-best month of the year

August is a reasonable time to visit Johnston for sightseeing. The water and warmth also suit a beach or pool day.

What to pack for Johnston in August

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

In August, Johnston sees daytime highs around 82°F and nights near 63°F. Pack light clothes. Worth having: rain gear and sun protection. About 9 days see rain.

light clothesrain gearsun protection

UV index in Johnston in August

LowModerateHighVery highExtreme

Clear-sky midday UV in August peaks around 7 — 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 August

GoodModeratePoorUnhealthyVery unhealthy

Average fine-particle pollution (PM2.5) through the year — so you can see where August 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
August 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).