Climate averages 1991–2020
Decatur weather
in August.
A hot, moderately wet month: the 2nd warmest and the 4th driest of the year.
Long-term climate patterns, not a forecast for a particular trip.
August is a hot month in Decatur: daytime highs average 28.3°C and nights cool to about 19.3°C. By daytime temperature it is the 2nd warmest of the 12 months.
Expect about 77 mm of rain on roughly 8 days, which makes August a moderately wet month (the 4th driest of the 12 months). Daylight, from sunrise to sunset, lasts about 13 h 44 min on an average August day.
The nearest other city in this atlas is Springfield (Illinois), United States (59 km away). In August its highs average 28.6°C, about as warm as Decatur, with 78 mm of rain.
Among the 498 cities listed in the United States, Decatur ranks joint 310th of 498 for the warmest August highs and 253rd of 498 for the driest August (rainfall, lowest first). The mean August high of those 498 cities is 29.9°C; Decatur is 1.6°C cooler than that mean.
From August to September, average highs fall by 3.3°C to 25.0°C, and monthly rainfall rises from 77 mm to 82 mm.
The annual picture
August in context
Monthly precipitation
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Decatur climate table
| Month | Average highHigh / low | Average low | Precipitation mm/month | Wet days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 1.8°C-6.3°C | -6.3°C | 69 | 8.5 | 9.710 h |
| February | 4.6°C-4.7°C | -4.7°C | 59 | 7.6 | 10.711 h |
| March | 10.7°C0.7°C | 0.7°C | 83 | 9.7 | 11.912 h |
| April | 17.2°C6.7°C | 6.7°C | 118 | 11.7 | 13.213 h |
| May | 22.5°C12.8°C | 12.8°C | 122 | 13.2 | 14.414 h |
| June | 27.1°C17.9°C | 17.9°C | 110 | 10.9 | 14.915 h |
| July | 28.8°C19.9°C | 19.9°C | 91 | 10.3 | 14.715 h |
| August, selected | 28.3°C19.3°C | 19.3°C | 77 | 8.4 | 13.714 h |
| September | 25.0°C15.4°C | 15.4°C | 82 | 7.3 | 12.512 h |
| October | 18.2°C9.1°C | 9.1°C | 88 | 8.6 | 11.211 h |
| November | 10.5°C2.3°C | 2.3°C | 88 | 8.7 | 10.010 h |
| December | 4.3°C-3.1°C | -3.1°C | 63 | 8.7 | 9.49 h |
Precipitation (rain or snow, as water) is the average of the 30 separate monthly totals. A wet day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
August in nearby cities
- Springfield (Illinois), United States in AugustUnited States · 59 kmHigh 28.6°C · Low 19.5°C · 78 mm rain
- Champaign in AugustUnited States · 68 kmHigh 27.9°C · Low 18.7°C · 74 mm rain
- Bloomington (Illinois), United States in AugustUnited States · 72 kmHigh 27.6°C · Low 18.7°C · 82 mm rain
- Peoria (Illinois), United States in AugustUnited States · 109 kmHigh 28.0°C · Low 19.4°C · 79 mm rain
- St. Louis in AugustUnited States · 172 kmHigh 30.4°C · Low 20.9°C · 74 mm rain
- Lafayette (Indiana), United States in AugustUnited States · 188 kmHigh 27.6°C · Low 18.4°C · 82 mm rain
- O'Fallon in AugustUnited States · 189 kmHigh 30.1°C · Low 20.9°C · 76 mm rain
- Joliet in AugustUnited States · 201 kmHigh 27.4°C · Low 18.5°C · 93 mm rain
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for Decatur) is explained once on the Decatur year overview and on the Sources, method and limits page.