Decatur weather in August

In August, Decatur sees average daytime highs of 83°F and overnight lows near 65°F, with 3.0 in of rain across 8.5 wet days and about 13.6 hours of daylight. It is the 2nd-warmest and 9th-wettest month of the year here.

Day-to-day highs hold fairly steady near 83°F through the month. The sky is clear or mostly clear about 42% of the time in August, and the air most often feels muggy.

Daylight stretches from about 14 h 06 min at the start of August to 13 hours by month's end. Set against the rest of the year, August is Decatur's 2nd-clearest and 12th-windiest month. For the whole year in context, see Decatur's year-round climate.

Daytime high
83°
2nd warmest
Overnight low
65°
11th coldest
Rainfall
3.0 in
8.5 wet days
Daylight
13 h 36 min
5:12 AM – 6:47 PM
Cloud cover
50%
2nd clearest
Wind
6 mph
12th windiest
Solar energy
5.74 kWh/m²
Travel score
6.1
out of 10

Decatur is city in Macon County, Illinois, United States.

Density
602/km²
people per km²
Founded
1823

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 83°F through the month.

A typical August day in Decatur reaches about 83°F in the afternoon and slips back to 65°F overnight — a 18°F spread between the day's warmth and the night's chill. On most days the high lands between 76°F and 91°F. Set against its neighbours, August runs on par with July and about 5°F warmer than September.

50°60°70°80°90°151015202531
Avg high (°F)Avg low (°F)
18467
28466
38466
48466
58466
68366
78366
88366
98366
108366
118365
128365
138365
148365
158365
168365
178365
188365
198365
208365
218365
228365
238365
248365
258365
268365
278364
288364
298364
308364
318364

How August really feels in Decatur

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.

Decatur weather by month

How August compares with the rest of the year at a glance. August is the 2nd-warmest and 9th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan36° / 21°2.78.549.50.0
Feb40° / 24°2.37.53.410.40.2
Mar52° / 34°3.39.71.511.72.7
Apr64° / 44°4.611.80.3135.3
May73° / 55°4.813.2014.26.2
Jun82° / 64°4.310.9014.86.0
Jul84° / 67°3.610.3014.55.5
Aug83° / 65°3.08.5013.66.1
Sep78° / 57°3.27.4012.37.3
Oct65° / 46°3.58.60.110.96.2
Nov51° / 35°3.58.70.89.82.7
Dec40° / 26°2.58.72.99.20.2

Cloud cover in August

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 42% 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 40%.

0%25%50%75%100%151015202531
Clearer (%)Cloudier (%)
15842
25842
35842
45842
55941
65941
75941
85941
95941
105941
115941
125941
136040
146040
156040
166139
176040
186139
196139
206040
216040
226040
236040
246040
256040
266040
276040
286139
296337
306337
316337

Chance of precipitation in August

Any precipitation

Decatur gets around 3.0 in of rain over 8.5 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 27% and peaks near 29% on the wettest days.

0%10%20%30%40%151015202531
Rain chance (%)
129
229
328
428
527
627
727
826
926
1026
1126
1226
1326
1426
1526
1626
1727
1827
1927
2027
2128
2228
2328
2428
2527
2627
2727
2826
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 27% of days. Sticky, muggy-or-worse air turns up on roughly 48% of them.

0%25%50%75%100%151015202531
Dry (%)Comfortable (%)Humid (%)Muggy (%)Oppressive (%)Miserable (%)
15162526261
25162527261
35162527251
45172528240
55172528240
66172529230
76182529230
86182429220
96182429220
107192429211
117192429211
127192428211
137202428201
148202428201
158202427201
168212427191
178212427191
189202427191
199202427191
209202527191
219202527191
229192527191
2310192527191
2410192527191
2511192527181
2611192527180
2712192526170
2814192526160
2915192526150
3016192426140
3117192426130

Wind in August

Winds average 6 mph in August, the calmest month.

Across August, daily wind ranges from about 6 mph on the calmest days to 7 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202531
Wind speed (mph)Feels
16calm
26calm
36calm
46calm
56calm
66calm
76calm
86calm
96calm
106calm
116calm
126calm
136calm
146calm
156calm
166calm
176calm
186calm
196calm
206calm
216calm
227calm
237calm
247calm
257calm
267calm
277calm
287calm
297calm
307calm
317calm

Sunrise & sunset in August

DaylightNight

Daylight runs from about 14 h 06 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 66 minutes over August. Sunrise moves from 4:58 AM to 5:27 AM, and sunset from 7:06 PM to 6:25 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202531
Daylight (h)Sunrise (AM)Sunset (PM)
114.14:587:06
214.14:597:05
314.15:007:04
414.05:017:02
514.05:027:01
614.05:037:00
713.95:046:59
813.95:056:58
913.85:066:57
1013.85:076:55
1113.85:086:54
1213.75:096:53
1313.75:096:51
1413.75:106:50
1513.65:116:49
1613.65:126:47
1713.55:136:46
1813.55:146:45
1913.55:156:43
2013.45:166:42
2113.45:176:40
2213.35:186:39
2313.35:196:37
2413.35:206:36
2513.25:216:34
2613.25:226:33
2713.15:236:31
2813.15:246:30
2913.05:256:28
3013.05:266:26
3113.05:276:25

Solar energy in August

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in August, about 5.74 kWh/m².

For context, solar energy here swings from a low near 1.8 kWh/m² to a high of 6.44 kWh/m² in June across the year — August's 5.74 kWh/m² falls in the middle.

0246151015202531
Solar energy (kWh/m²)Level
16.2Intense
26.2Intense
36.1Intense
46.1Intense
56.1Intense
66.0Intense
76.0Intense
86.0Bright
96.0Bright
105.9Bright
115.9Bright
125.9Bright
135.8Bright
145.8Bright
155.8Bright
165.7Bright
175.7Bright
185.7Bright
195.6Bright
205.6Bright
215.6Bright
225.5Bright
235.5Bright
245.5Bright
255.5Bright
265.4Bright
275.4Bright
285.4Bright
295.3Bright
305.3Bright
315.3Bright
Planning a trip in August

Hazard calendar for Decatur

In seasonPeak

In August, Decatur sits inside its atlantic hurricane season. The full year is below, with each hazard's peak months called out.

Decatur sits in the Atlantic hurricane belt; the season peaks August–October.

Atlantic hurricane
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

Is August a good time to visit Decatur?

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

6.1
Sightseeing
4th-best month of the year
7.3
Beach & pool
1st-best month of the year

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

What to pack for Decatur in August

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

In August, Decatur sees daytime highs around 83°F and nights near 65°F. Pack light clothes. Worth having: rain gear and sun protection. About 9 days see rain.

light clothesrain gearsun protection

UV index in Decatur in August

LowModerateHighVery highExtreme

Clear-sky midday UV in August peaks around 8 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Decatur peaks around June 22 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 9 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highHighModerateJun 22UV 9Jan 1UV 2
UV index (midday)Level
Jan2Low
Feb3Moderate
Mar5Moderate
Apr6High
May8Very high
Jun9Very high
Jul9Very high
Aug8Very high
Sep6High
Oct4Moderate
Nov3Moderate
Dec2Low

Air quality in Decatur 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 Decatur is worst in July — around 17 µg/m³ PM2.5 (moderate), about 2.1× the cleanest month (October, 8 µg/m³).

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

01020JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodModerateGoodJul 1716 µg/m³Oct 228 µg/m³
PM2.5 (µg/m³)Level
Jan10Good
Feb13Moderate
Mar12Moderate
Apr11Good
May14Moderate
Jun14Moderate
Jul17Moderate
Aug15Moderate
Sep12Good
Oct8Good
Nov8Good
Dec9Good
Location & terrain

Where is Decatur?

Decatur sits at 39.8°N, 89.0°W, 673 ft above sea level, in United States. The nearest listed city is Springfield, 37 mi away.

Topography around Decatur

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

Within 2 miles, the terrain around Decatur has only modest variations in elevation — a maximum elevation change of 164 ft around an average of 666 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 197 ft; within 50 miles, only modest variations in elevation — a maximum elevation change of 489 ft.

The land around Decatur is covered by trees (43%) and artificial surfaces (34%) within 2 miles, cropland (68%) within 10 miles, and cropland (83%) within 50 miles.

2 miles
164 ft
10 miles
197 ft
50 miles
489 ft
treesgrasslandcroplandartificial surfacesbare terrainwater
August weather nearby: Springfield 37 mi · Mattoon 40 mi · Champaign 42 mi · Urbana 43 mi · Bloomington 45 mi · Normal 47 mi · Charleston 48 mi · Morton 60 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 Decatur (39.8403°, -88.9548°, elevation 673 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. Tropical-cyclone seasons are the published climatological basin seasons (NOAA National Hurricane Center / regional warning centres). 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).