Decatur weather in December: Decatur, Illinois: normal highs, lows, rain and records for December
Decatur in December has a normal high of 40°F and a normal low of 25°F, a daily mean of 32°F, falling from 45°F on the 1st to 36°F by the 31st. Measurable precipitation falls on 9 days in a normal December, 2.12 inches in all. (NOAA 1991-2020 normals)
In metric: a normal high of 4°C and low of −4°C, 54 mm of precipitation in December.
- NOAA stationDecatur Airport
- Station IDUSW00003887
- Location39.83°N 88.87°W
- Elevation675 ft (206 m)
- From the center4 miles
- Population68,763
- Jan 35° 20°
- Feb 40° 23°
- Mar 52° 32°
- Apr 64° 42°
- May 74° 53°
- Jun 83° 62°
- Jul 86° 66°
- Aug 84° 63°
- Sep 79° 55°
- Oct 66° 44°
- Nov 51° 34°
- Dec 40° 25°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
How warm is Decatur in December?
The normal high is 40°F and the normal low 25°F, for a daily mean of 32.4°F. December is 10.3°F cooler than November and 5.0°F warmer than January. December is the 10th warmest month of the year in Decatur and the 10th wettest. Across the month the normal high falls 9°F, from 45°F on December 1 to 36°F on December 31. From one year to the next December's mean temperature typically moves about 4.6°F either way (NOAA's standard deviation), so roughly two Decembers in three average between 28°F and 37°F.
Bars above: each day's normal high to low. Columns below: the chance of 0.01 inch or more of precipitation that day, on a scale of 0 to 100% (highest 31%).
| Day | High | Low | Chance of 0.01 in | Chance of 0.10 in |
|---|---|---|---|---|
| December 1 | 45°F | 29°F | 31% | 17% |
| December 8 | 42°F | 27°F | 30% | 17% |
| December 15 | 40°F | 25°F | 30% | 16% |
| December 22 | 38°F | 24°F | 29% | 16% |
| December 31 | 36°F | 22°F | 28% | 15% |
Every day of December: normal high, low and chance of precipitation (warmest afternoon December 1, coldest night December 31)
| Day | High | Low | Chance of 0.01 in | Chance of 0.10 in | Daylight |
|---|---|---|---|---|---|
| December 1 | 45°F | 29°F | 31% | 17% | 9 h 30 min |
| December 2 | 44°F | 29°F | 31% | 17% | 9 h 30 min |
| December 3 | 44°F | 29°F | 31% | 17% | 9 h 30 min |
| December 4 | 43°F | 28°F | 31% | 17% | 9 h 30 min |
| December 5 | 43°F | 28°F | 31% | 17% | 9 h 30 min |
| December 6 | 43°F | 28°F | 31% | 17% | 9 h 30 min |
| December 7 | 42°F | 27°F | 30% | 17% | 9 h 30 min |
| December 8 | 42°F | 27°F | 30% | 17% | 9 h 30 min |
| December 9 | 42°F | 27°F | 30% | 16% | 9 h 30 min |
| December 10 | 41°F | 27°F | 30% | 16% | 9 h 30 min |
| December 11 | 41°F | 26°F | 30% | 16% | 9 h 20 min |
| December 12 | 41°F | 26°F | 30% | 16% | 9 h 20 min |
| December 13 | 40°F | 26°F | 30% | 16% | 9 h 20 min |
| December 14 | 40°F | 26°F | 30% | 16% | 9 h 20 min |
| December 15 | 40°F | 25°F | 30% | 16% | 9 h 20 min |
| December 16 | 39°F | 25°F | 30% | 16% | 9 h 20 min |
| December 17 | 39°F | 25°F | 30% | 16% | 9 h 20 min |
| December 18 | 39°F | 25°F | 30% | 16% | 9 h 20 min |
| December 19 | 39°F | 24°F | 29% | 16% | 9 h 20 min |
| December 20 | 38°F | 24°F | 29% | 16% | 9 h 20 min |
| December 21 | 38°F | 24°F | 29% | 16% | 9 h 20 min |
| December 22 | 38°F | 24°F | 29% | 16% | 9 h 20 min |
| December 23 | 38°F | 24°F | 29% | 16% | 9 h 20 min |
| December 24 | 37°F | 23°F | 29% | 15% | 9 h 20 min |
| December 25 | 37°F | 23°F | 29% | 15% | 9 h 20 min |
| December 26 | 37°F | 23°F | 28% | 15% | 9 h 20 min |
| December 27 | 37°F | 23°F | 28% | 15% | 9 h 20 min |
| December 28 | 36°F | 23°F | 28% | 15% | 9 h 20 min |
| December 29 | 36°F | 22°F | 28% | 15% | 9 h 20 min |
| December 30 | 36°F | 22°F | 28% | 15% | 9 h 20 min |
| December 31 | 36°F | 22°F | 28% | 15% | 9 h 20 min |
- Normal high
- 40°FDecember average
- Normal low
- 25°FDecember average
- Precipitation
- 2.12 inmonth total
- Days with precipitation
- 90.01 inch or more
- Nights at 32°F or colder
- 24
- Daylight
- 9 h 30 min to 9 h 20 minDecember 1 to December 31
- Sunshine
- 61%of clear-sky sunlight (NASA)
Source: NOAA NCEI 1991-2020 daily normals, station USW00003887; monthly normals. Daylight is computed from the place's latitude with NOAA's solar equations.
Does it rain in Decatur in December?
On a given December day the chance of 0.01 inch or more is 29% on average, highest around December 1 (31%). In all, 2.12 in falls on 9 days of a normal December.
In a normal December in Decatur, 24 nights fall to freezing and 8 days stay below freezing all day.
Source: NOAA NCEI 1991-2020 daily and monthly normals, station USW00003887.
How humid and windy is Decatur in December?
At 3 p.m. the normal temperature is 34°F with 70% relative humidity and a dew point of 25°F; at 6 a.m. it is 26°F with 83% humidity. The wind averages 11.1 mph, most often from the west-southwest in the afternoon. A dew point under 50°F feels dry.
| Time | Temperature | Dew point | Humidity | Wind | Clear or few clouds |
|---|---|---|---|---|---|
| 6 a.m. | 26°F | 22°F | 83% | 10.1 mph | 47% |
| 9 a.m. | 28°F | 23°F | 80% | 11.4 mph | 44% |
| noon | 33°F | 24°F | 72% | 12.5 mph | 43% |
| 3 p.m. | 34°F | 25°F | 70% | 12.4 mph | 47% |
| 6 p.m. | 31°F | 25°F | 77% | 11.0 mph | – |
| 9 p.m. | 29°F | 24°F | 80% | 11.0 mph | 49% |
Source: NOAA NCEI 1991-2020 hourly normals, station USW00003887. Hourly normals exist only for NOAA's first-order stations; a dash where NOAA publishes no value for that hour (the sky at some hours).
What are the records for December in Decatur?
The warmest December temperature on this station's record (since 2000) is 72°F, on December 3, 2012; the coldest is −14°F, on December 14, 2025. The wettest December brought 9.22 in (2015).
The December mean against the 1991-2020 normal of 32.4°F: 2021 41.2°F (+8.8), 2022 32.1°F (−0.3), 2023 39.9°F (+7.5), 2024 35.7°F (+3.3), 2025 29.2°F (−3.2). 3 of 5 ran warmer than normal.
| December | Mean | Against normal | Precip. |
|---|---|---|---|
| 2021 | 41.2°F | +8.8°F | 2.32 in |
| 2022 | 32.1°F | −0.3°F | 2.00 in |
| 2023 | 39.9°F | +7.5°F | 2.88 in |
| 2024 | 35.7°F | +3.3°F | 1.73 in |
| 2025 | 29.2°F | −3.2°F | – |
Source: records: ACIS, station USW00003887; recent months: ACIS, station USW00003887. Records and recent months use complete months only.
How does December in Decatur compare across Illinois?
Across the 144 places PlainClimate covers in Illinois, December normal highs run from 33°F in Galena to 48°F in Anna; Decatur's is 40°F.
Source: NOAA NCEI 1991-2020 monthly normals for every station in the state.