Chatham climate — normals and trends
Chatham (United States) has a hot-summer humid continental climate (Dfa) under the Köppen-Geiger classification. Its mean annual temperature is 9.9 °C and it receives 1,081 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 (23.8 °C on average) and the coldest is January (-4.5 °C). Rainfall peaks in April.
Chatham averages 101 frost days, 9 hot days (≥ 30 °C) and 126 rainy days per year.
Chatham has warmed by +1.3 °C between 1940 and 2025, or +0.15 °C per decade. This trend is statistically significant.
The number of frost days there went from about 118 to 84 per year over the period.
The hottest day of the period reached 36.3 °C (on 13 July 1995) and the coldest -30.7 °C (on 19 January 1994).
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
ChathamIllinois
- coords
- 41.74°, -87.61°
- period
- 1940–2025 · 86 yrs
Mean daily temperature
9.9°C
Average daily high
12.5°C
Average daily low
7.6°C
Annual rainfall
1,081mm
Sunshine / day
8.9h
Mean relative humidity
75%
Average peak wind
28.7km/h
Seasonal range
28.3°C
Frost days (< 0 °C)
101 d/yr
Hot days (≥ 30 °C)
9 d/yr
Rainy days (≥ 1 mm)
126 d/yr
Annual snowfall
75.8 cm
Average feels-like high
10.1 °C
Average feels-like low
3.7 °C
Average peak gust
40.9 km/h
Tropical nights (≥ 20 °C)
63 d/yr
Solar radiation
15.3 MJ/m²
Has the climate changed?
One stripe per year, 1940 to 2025
+1.3 °C
since 1940
+0.2 °C per decade · r² = 0.18 · 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
36.3 °C
13 July 1995
Coldest day
-30.7 °C
19 January 1994
Wettest day
92 mm
26 August 1987
Windiest day
70.4 km/h
22 February 1974
Strongest gust
101.9 km/h
11 November 1940
Hottest feels-like
43.9 °C
14 July 1995
Coldest feels-like
-39.7 °C
20 January 1985
Snowiest day
23.3 cm
2 January 1999
Sunniest day
14.6 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 | -0.9 °C | +0.7 °C | 43 mm | -35 mm |
| Feb | 0.3 °C | +1.0 °C | 32 mm | -32 mm |
| Mar | 8.0 °C | +4.7 °C | 98 mm | +7 mm |
| Apr | 10.8 °C | +1.3 °C | 87 mm | -25 mm |
| May | 13.7 °C | -3.6 °C | 111 mm | +5 mm |
| Jun | 22.6 °C | -1.2 °C | 113 mm | +17 mm |
| Jul | 26.4 °C | 0.0 °C | 123 mm | +38 mm |
| Aug | 24.5 °C | -1.2 °C | 81 mm | -4 mm |
| Sep | 21.9 °C | 0.0 °C | 21 mm | -64 mm |
| Oct | 16.9 °C | +1.6 °C | 128 mm | +34 mm |
| Nov | 8.9 °C | +1.0 °C | 85 mm | -11 mm |
| Dec | 1.4 °C | -0.3 °C | 105 mm | +16 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 Chatham?
Chatham has a hot-summer humid continental climate (Köppen Dfa). Over 1940-2025, the average annual temperature is 9.9 °C and it receives 1,081 mm of precipitation per year.
What is the hottest day ever recorded in Chatham?
The hottest day measured in Chatham between 1940 and 2025 was 13 July 1995, reaching 36.3 °C.
What is the coldest day in Chatham?
The coldest day measured in Chatham between 1940 and 2025 was 19 January 1994, at -30.7 °C.
Does it snow in Chatham?
Yes. Chatham gets on average 75.8 cm of snow per year and has around 101 frost days.
Has the climate of Chatham warmed?
Yes: Chatham warmed by +1.3 °C between 1940 and 2025, a statistically significant trend.
What is the wettest day in Chatham?
The wettest day measured in Chatham between 1940 and 2025 was 26 August 1987, with 92 mm of rain in 24 hours.
What was the windiest day in Chatham?
The windiest day measured in Chatham between 1940 and 2025 was 22 February 1974, with winds reaching 70.4 km/h.
What is the warmest month in Chatham?
The warmest month in Chatham is July (23.8 °C on average); the coldest is January (-4.5 °C).
How much does it rain in Chatham?
Chatham receives on average 1,081 mm of precipitation per year, spread over about 126 rainy days.
Is it sunny in Chatham?
Chatham 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 Chatham?
The heaviest 24-hour snowfall measured in Chatham between 1940 and 2025 was 2 January 1999, with 23.3 cm.
Are there tropical nights in Chatham?
Yes: Chatham has on average 63 tropical nights per year (temperature staying above 20 °C), over 1940-2025.
What was the most extreme apparent temperature in Chatham?
In Chatham, between 1940 and 2025, the highest apparent temperature reached 43.9 °C on 14 July 1995, and the lowest was -39.7 °C on 20 January 1985.
Compare Chatham with another city
Pick a second city: its normals will be set against these, indicator by indicator.
Nearby cities
The climate around Chatham