Decatur weather in August: Decatur, Illinois: normal highs, lows, rain and records for August
Decatur in August has a normal high of 84°F and a normal low of 63°F, a daily mean of 74°F, falling from 85°F on the 1st to 83°F by the 31st. Measurable precipitation falls on 9 days in a normal August, 3.03 inches in all. (NOAA 1991-2020 normals)
In metric: a normal high of 29°C and low of 17°C, 77 mm of precipitation in August.
- NOAA stationDecatur Airport
- Station IDUSW00003887
- Location39.83°N 88.87°W
- Elevation675 ft (206 m)
- From the center4 miles
- Population68,763
- Jan 35° 20°
- Feb 40° 23°
- Mar 52° 32°
- Apr 64° 42°
- May 74° 53°
- Jun 83° 62°
- Jul 86° 66°
- Aug 84° 63°
- Sep 79° 55°
- Oct 66° 44°
- Nov 51° 34°
- Dec 40° 25°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
How warm is Decatur in August?
The normal high is 84°F and the normal low 63°F, for a daily mean of 73.7°F. August is 2.0°F cooler than July and 6.7°F warmer than September. August is the 2nd warmest month of the year in Decatur and the 6th wettest. Across the month the normal high falls 2°F, from 85°F on August 1 to 83°F on August 31. From one year to the next August's mean temperature typically moves about 2.6°F either way (NOAA's standard deviation), so roughly two Augusts in three average between 71°F and 76°F.
Bars above: each day's normal high to low. Columns below: the chance of 0.01 inch or more of precipitation that day, on a scale of 0 to 100% (highest 31%).
| Day | High | Low | Chance of 0.01 in | Chance of 0.10 in |
|---|---|---|---|---|
| August 1 | 85°F | 65°F | 29% | 16% |
| August 8 | 85°F | 64°F | 29% | 16% |
| August 15 | 85°F | 64°F | 30% | 17% |
| August 22 | 84°F | 62°F | 31% | 17% |
| August 31 | 83°F | 60°F | 31% | 17% |
Every day of August: normal high, low and chance of precipitation (warmest afternoon August 1, coldest night August 31)
| Day | High | Low | Chance of 0.01 in | Chance of 0.10 in | Daylight |
|---|---|---|---|---|---|
| August 1 | 85°F | 65°F | 29% | 16% | 14 h 20 min |
| August 2 | 85°F | 65°F | 29% | 16% | 14 h 20 min |
| August 3 | 85°F | 65°F | 29% | 16% | 14 h 10 min |
| August 4 | 85°F | 65°F | 29% | 16% | 14 h 10 min |
| August 5 | 85°F | 65°F | 29% | 16% | 14 h 10 min |
| August 6 | 85°F | 65°F | 29% | 16% | 14 h 10 min |
| August 7 | 85°F | 65°F | 29% | 16% | 14 h |
| August 8 | 85°F | 64°F | 29% | 16% | 14 h |
| August 9 | 85°F | 64°F | 29% | 16% | 14 h |
| August 10 | 85°F | 64°F | 29% | 16% | 14 h |
| August 11 | 85°F | 64°F | 29% | 16% | 14 h |
| August 12 | 85°F | 64°F | 29% | 16% | 13 h 50 min |
| August 13 | 85°F | 64°F | 30% | 17% | 13 h 50 min |
| August 14 | 85°F | 64°F | 30% | 17% | 13 h 50 min |
| August 15 | 85°F | 64°F | 30% | 17% | 13 h 50 min |
| August 16 | 84°F | 63°F | 30% | 17% | 13 h 50 min |
| August 17 | 84°F | 63°F | 30% | 17% | 13 h 40 min |
| August 18 | 84°F | 63°F | 30% | 17% | 13 h 40 min |
| August 19 | 84°F | 63°F | 31% | 17% | 13 h 40 min |
| August 20 | 84°F | 63°F | 31% | 17% | 13 h 40 min |
| August 21 | 84°F | 63°F | 31% | 17% | 13 h 30 min |
| August 22 | 84°F | 62°F | 31% | 17% | 13 h 30 min |
| August 23 | 84°F | 62°F | 31% | 17% | 13 h 30 min |
| August 24 | 84°F | 62°F | 31% | 17% | 13 h 30 min |
| August 25 | 84°F | 62°F | 31% | 17% | 13 h 20 min |
| August 26 | 84°F | 62°F | 31% | 17% | 13 h 20 min |
| August 27 | 83°F | 61°F | 31% | 17% | 13 h 20 min |
| August 28 | 83°F | 61°F | 31% | 17% | 13 h 20 min |
| August 29 | 83°F | 61°F | 31% | 17% | 13 h 10 min |
| August 30 | 83°F | 61°F | 31% | 17% | 13 h 10 min |
| August 31 | 83°F | 60°F | 31% | 17% | 13 h 10 min |
- Normal high
- 84°FAugust average
- Normal low
- 63°FAugust average
- Precipitation
- 3.03 inmonth total
- Days with precipitation
- 90.01 inch or more
- Days at 90°F or more
- 7
- Daylight
- 14 h 20 min to 13 h 10 minAugust 1 to August 31
- Days at 70°F or more
- 31
- Days at 80°F or more
- 26
- Sunshine
- 82%of clear-sky sunlight (NASA)
Source: NOAA NCEI 1991-2020 daily normals, station USW00003887; monthly normals. Daylight is computed from the place's latitude with NOAA's solar equations.
Does it rain in Decatur in August?
On a given August day the chance of 0.01 inch or more is 30% on average, highest around August 29 (31%). In all, 3.03 in falls on 9 days of a normal August, 1 of them with an inch or more.
In a normal August in Decatur, 7 days reach 90°F.
Source: NOAA NCEI 1991-2020 daily and monthly normals, station USW00003887.
How humid and windy is Decatur in August?
At 3 p.m. the normal temperature is 83°F with 51% relative humidity and a dew point of 63°F; at 6 a.m. it is 64°F with 89% humidity. The wind averages 6.9 mph, most often from the south-southwest in the afternoon.
| Time | Temperature | Dew point | Humidity | Wind | Clear or few clouds |
|---|---|---|---|---|---|
| 6 a.m. | 64°F | 60°F | 89% | 5.0 mph | 69% |
| 9 a.m. | 75°F | 64°F | 69% | 8.2 mph | 69% |
| noon | 81°F | 63°F | 55% | 9.2 mph | 63% |
| 3 p.m. | 83°F | 63°F | 51% | 9.6 mph | 66% |
| 6 p.m. | 78°F | 64°F | 63% | 7.4 mph | 76% |
| 9 p.m. | 70°F | 63°F | 81% | 5.4 mph | 80% |
Source: NOAA NCEI 1991-2020 hourly normals, station USW00003887. Hourly normals exist only for NOAA's first-order stations; a dash where NOAA publishes no value for that hour (the sky at some hours).
What are the records for August in Decatur?
The warmest August temperature on this station's record (since 2000) is 100°F, on August 12, 2007; the coldest is 46°F, on August 16, 2004. The wettest August brought 11.32 in (2022).
The August mean against the 1991-2020 normal of 73.7°F: 2021 76.1°F (+2.4), 2022 73.7°F (at normal), 2023 74.2°F (+0.5), 2024 74.5°F (+0.8), 2025 74.7°F (+1.0), 2026 74.8°F (+1.1). 5 of 6 ran warmer than normal.
| August | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 76.1°F | +2.4°F | 1.65 in |
| 2022 | 73.7°F | at normal | 11.32 in |
| 2023 | 74.2°F | +0.5°F | 4.87 in |
| 2024 | 74.5°F | +0.8°F | 2.59 in |
| 2025 | 74.7°F | +1.0°F | 1.56 in |
| 2026 | 74.8°F | +1.1°F | 3.78 in |
Source: records: ACIS, station USW00003887; recent months: ACIS, station USW00003887. Records and recent months use complete months only.
How does August in Decatur compare across Illinois?
Across the 144 places PlainClimate covers in Illinois, August normal highs run from 79°F in Barrington to 89°F in Anna; Decatur's is 84°F.
Source: NOAA NCEI 1991-2020 monthly normals for every station in the state.