Decatur climate — normals and trends
Decatur (United States) has a hot-summer humid continental climate (Dfa) under the Köppen-Geiger classification. Its mean annual temperature is 11.7 °C and it receives 986 mm of precipitation per year.
These figures are normals computed over 86 complete calendar years, from 1940 to 2025, using ERA5 reanalysis data from the Copernicus programme.
The warmest month is July (24.4 °C on average) and the coldest is January (-2.9 °C). Rainfall peaks in April.
Decatur averages 103 frost days, 39 hot days (≥ 30 °C) and 111 rainy days per year.
Decatur has warmed by +1.7 °C between 1940 and 2025, or +0.20 °C per decade. This trend is statistically significant.
The number of frost days there went from about 115 to 91 per year over the period.
The hottest day of the period reached 39.4 °C (on 16 August 1988) and the coldest -30.9 °C (on 17 January 1982).
Data from ERA5 reanalysis (Copernicus Climate Change Service), redistributed under a CC-BY 4.0 licence. Normals are recomputed whenever the archive is updated.
Climate normals · ERA5
DecaturIllinois
- coords
- 39.84°, -88.95°
- period
- 1940–2025 · 86 yrs
Mean daily temperature
11.7°C
Average daily high
16.6°C
Average daily low
6.9°C
Annual rainfall
986mm
Sunshine / day
8.9h
Mean relative humidity
70%
Average peak wind
19.9km/h
Seasonal range
27.3°C
Frost days (< 0 °C)
103 d/yr
Hot days (≥ 30 °C)
39 d/yr
Rainy days (≥ 1 mm)
111 d/yr
Annual snowfall
47.1 cm
Average feels-like high
14.9 °C
Average feels-like low
4.2 °C
Average peak gust
38.5 km/h
Tropical nights (≥ 20 °C)
43 d/yr
Solar radiation
15.4 MJ/m²
Has the climate changed?
One stripe per year, 1940 to 2025
+1.7 °C
since 1940
+0.2 °C per decade · r² = 0.31 · p = < 0.001
Trend fitted by linear regression (ordinary least squares) on annual means. A trend is shown only when it is statistically significant (p < 0.05).
A climograph overlays rainfall (bars) and temperature (line): the standard reading in climatology, where you can see at a glance whether the warm season is also the dry one.
Records for the period
Hottest day
39.4 °C
16 August 1988
Coldest day
-30.9 °C
17 January 1982
Wettest day
84 mm
9 September 1992
Windiest day
58.1 km/h
5 April 1947
Strongest gust
106.6 km/h
12 November 1982
Hottest feels-like
45.1 °C
16 August 1988
Coldest feels-like
-38.1 °C
20 January 1985
Snowiest day
30.0 cm
6 November 1951
Sunniest day
14.1 h
21 June 1940
Normals computed over complete calendar years 1940–2025.
A specific year
Pick a year and see how it compares to normal — warmer, drier or more extreme than usual?
Across the whole year
Month by month
| High | vs. normal | Precipitation | vs. normal | |
|---|---|---|---|---|
| Jan | -0.3 °C | -1.5 °C | 35 mm | -26 mm |
| Feb | 4.1 °C | +0.2 °C | 24 mm | -37 mm |
| Mar | 15.7 °C | +5.5 °C | 74 mm | -18 mm |
| Apr | 18.7 °C | +1.5 °C | 132 mm | +24 mm |
| May | 22.5 °C | -0.2 °C | 90 mm | -17 mm |
| Jun | 28.4 °C | +0.8 °C | 141 mm | +44 mm |
| Jul | 30.1 °C | +1.0 °C | 124 mm | +38 mm |
| Aug | 28.3 °C | -0.2 °C | 23 mm | -51 mm |
| Sep | 28.2 °C | +2.8 °C | 45 mm | -31 mm |
| Oct | 21.5 °C | +2.6 °C | 50 mm | -29 mm |
| Nov | 11.9 °C | +1.3 °C | 60 mm | -21 mm |
| Dec | 3.7 °C | -0.1 °C | 43 mm | -22 mm |
The year's extremes
What was the weather like that day?
Your birthday, a wedding, a memorable trip: discover the actual weather for any date since 1940.
Frequently asked questions
What is the climate of Decatur?
Decatur has a hot-summer humid continental climate (Köppen Dfa). Over 1940-2025, the average annual temperature is 11.7 °C and it receives 986 mm of precipitation per year.
What is the hottest day ever recorded in Decatur?
The hottest day measured in Decatur between 1940 and 2025 was 16 August 1988, reaching 39.4 °C.
What is the coldest day in Decatur?
The coldest day measured in Decatur between 1940 and 2025 was 17 January 1982, at -30.9 °C.
Does it snow in Decatur?
Yes. Decatur gets on average 47.1 cm of snow per year and has around 103 frost days.
Has the climate of Decatur warmed?
Yes: Decatur warmed by +1.7 °C between 1940 and 2025, a statistically significant trend.
What is the wettest day in Decatur?
The wettest day measured in Decatur between 1940 and 2025 was 9 September 1992, with 84 mm of rain in 24 hours.
What was the windiest day in Decatur?
The windiest day measured in Decatur between 1940 and 2025 was 5 April 1947, with winds reaching 58.1 km/h.
What is the warmest month in Decatur?
The warmest month in Decatur is July (24.4 °C on average); the coldest is January (-2.9 °C).
How much does it rain in Decatur?
Decatur receives on average 986 mm of precipitation per year, spread over about 111 rainy days.
Is it sunny in Decatur?
Decatur gets on average 8.9 hours of sunshine per day, roughly 3,249 hours per year over 1940-2025.
What is the biggest single-day snowfall in Decatur?
The heaviest 24-hour snowfall measured in Decatur between 1940 and 2025 was 6 November 1951, with 30.0 cm.
Are there tropical nights in Decatur?
Yes: Decatur has on average 43 tropical nights per year (temperature staying above 20 °C), over 1940-2025.
What was the most extreme apparent temperature in Decatur?
In Decatur, between 1940 and 2025, the highest apparent temperature reached 45.1 °C on 16 August 1988, and the lowest was -38.1 °C on 20 January 1985.
Compare Decatur with another city
Pick a second city: its normals will be set against these, indicator by indicator.
Nearby cities
The climate around Decatur