Oak Forest climate — normals and trends
Oak Forest (United States) has a hot-summer humid continental climate (Dfa) under the Köppen-Geiger classification. Its mean annual temperature is 10.0 °C and it receives 956 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 (23.2 °C on average) and the coldest is January (-4.7 °C). Rainfall peaks in May.
Oak Forest averages 118 frost days, 27 hot days (≥ 30 °C) and 120 rainy days per year.
Oak Forest has warmed by +2.1 °C between 1940 and 2025, or +0.25 °C per decade. This trend is statistically significant.
The number of frost days there went from about 132 to 104 per year over the period.
The hottest day of the period reached 39.1 °C (on 25 June 1988) and the coldest -31.7 °C (on 31 January 2019).
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
Oak ForestIllinois
- coords
- 41.60°, -87.74°
- period
- 1940–2025 · 86 yrs
Mean daily temperature
10.0°C
Average daily high
14.7°C
Average daily low
5.5°C
Annual rainfall
956mm
Sunshine / day
8.9h
Mean relative humidity
71%
Average peak wind
19.9km/h
Seasonal range
27.9°C
Frost days (< 0 °C)
118 d/yr
Hot days (≥ 30 °C)
27 d/yr
Rainy days (≥ 1 mm)
120 d/yr
Annual snowfall
69.7 cm
Average feels-like high
12.8 °C
Average feels-like low
2.5 °C
Average peak gust
39.8 km/h
Tropical nights (≥ 20 °C)
28 d/yr
Solar radiation
15.1 MJ/m²
Has the climate changed?
One stripe per year, 1940 to 2025
+2.1 °C
since 1940
+0.3 °C per decade · r² = 0.41 · 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
39.1 °C
25 June 1988
Coldest day
-31.7 °C
31 January 2019
Wettest day
87 mm
25 June 2021
Windiest day
53.7 km/h
11 November 1940
Strongest gust
109.1 km/h
10 November 1998
Hottest feels-like
45.3 °C
14 July 1995
Coldest feels-like
-38.0 °C
20 January 1985
Snowiest day
23.4 cm
2 January 1999
Sunniest day
14.5 h
12 June 2012
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 | -1.0 °C | -0.1 °C | 31 mm | -23 mm |
| Feb | 1.9 °C | +0.6 °C | 23 mm | -27 mm |
| Mar | 13.1 °C | +5.5 °C | 110 mm | +29 mm |
| Apr | 15.9 °C | +1.1 °C | 90 mm | -14 mm |
| May | 19.6 °C | -1.2 °C | 111 mm | +5 mm |
| Jun | 28.1 °C | +2.0 °C | 151 mm | +48 mm |
| Jul | 29.3 °C | +1.2 °C | 134 mm | +42 mm |
| Aug | 26.7 °C | -0.5 °C | 88 mm | +4 mm |
| Sep | 25.9 °C | +2.3 °C | 38 mm | -39 mm |
| Oct | 19.2 °C | +2.0 °C | 109 mm | +34 mm |
| Nov | 9.7 °C | +0.9 °C | 59 mm | -11 mm |
| Dec | 1.3 °C | -0.6 °C | 63 mm | +2 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 Oak Forest?
Oak Forest has a hot-summer humid continental climate (Köppen Dfa). Over 1940-2025, the average annual temperature is 10.0 °C and it receives 956 mm of precipitation per year.
What is the hottest day ever recorded in Oak Forest?
The hottest day measured in Oak Forest between 1940 and 2025 was 25 June 1988, reaching 39.1 °C.
What is the coldest day in Oak Forest?
The coldest day measured in Oak Forest between 1940 and 2025 was 31 January 2019, at -31.7 °C.
Does it snow in Oak Forest?
Yes. Oak Forest gets on average 69.7 cm of snow per year and has around 118 frost days.
Has the climate of Oak Forest warmed?
Yes: Oak Forest warmed by +2.1 °C between 1940 and 2025, a statistically significant trend.
What is the wettest day in Oak Forest?
The wettest day measured in Oak Forest between 1940 and 2025 was 25 June 2021, with 87 mm of rain in 24 hours.
What was the windiest day in Oak Forest?
The windiest day measured in Oak Forest between 1940 and 2025 was 11 November 1940, with winds reaching 53.7 km/h.
What is the warmest month in Oak Forest?
The warmest month in Oak Forest is July (23.2 °C on average); the coldest is January (-4.7 °C).
How much does it rain in Oak Forest?
Oak Forest receives on average 956 mm of precipitation per year, spread over about 120 rainy days.
Is it sunny in Oak Forest?
Oak Forest 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 Oak Forest?
The heaviest 24-hour snowfall measured in Oak Forest between 1940 and 2025 was 2 January 1999, with 23.4 cm.
Are there tropical nights in Oak Forest?
Yes: Oak Forest has on average 28 tropical nights per year (temperature staying above 20 °C), over 1940-2025.
What was the most extreme apparent temperature in Oak Forest?
In Oak Forest, between 1940 and 2025, the highest apparent temperature reached 45.3 °C on 14 July 1995, and the lowest was -38.0 °C on 20 January 1985.
Compare Oak Forest with another city
Pick a second city: its normals will be set against these, indicator by indicator.
Nearby cities
The climate around Oak Forest