Climate averages 1991–2020
Decatur weather
in May.
A warm, wet month: the 5th warmest and the wettest of the year.
Long-term climate patterns, not a forecast for a particular trip.
May is a warm month in Decatur: daytime highs average 22.5°C and nights cool to about 12.8°C. By daytime temperature it is the 5th warmest of the 12 months.
Expect about 122 mm of rain on roughly 13 days, which makes May a wet month (the wettest month of the year). Daylight, from sunrise to sunset, lasts about 14 h 21 min on an average May day.
The nearest other city in this atlas is Springfield (Illinois), United States (59 km away). In May its highs average 22.7°C, about as warm as Decatur, with 117 mm of rain.
Among the 498 cities listed in the United States, Decatur ranks joint 277th of 498 for the warmest May highs and joint 450th of 498 for the driest May (rainfall, lowest first). The mean May high of those 498 cities is 23.8°C; Decatur is 1.3°C cooler than that mean.
From May to June, average highs rise by 4.6°C to 27.1°C, and monthly rainfall falls from 122 mm to 110 mm.
The annual picture
May 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, selected | 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 | 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
May in nearby cities
- Springfield (Illinois), United States in MayUnited States · 59 kmHigh 22.7°C · Low 13.0°C · 117 mm rain
- Champaign in MayUnited States · 68 kmHigh 22.2°C · Low 12.2°C · 118 mm rain
- Bloomington (Illinois), United States in MayUnited States · 72 kmHigh 21.9°C · Low 11.9°C · 119 mm rain
- Peoria (Illinois), United States in MayUnited States · 109 kmHigh 22.1°C · Low 12.5°C · 117 mm rain
- St. Louis in MayUnited States · 172 kmHigh 24.3°C · Low 14.3°C · 128 mm rain
- Lafayette (Indiana), United States in MayUnited States · 188 kmHigh 21.9°C · Low 11.9°C · 109 mm rain
- O'Fallon in MayUnited States · 189 kmHigh 23.8°C · Low 14.3°C · 123 mm rain
- Joliet in MayUnited States · 201 kmHigh 21.2°C · Low 11.0°C · 116 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.