Decatur, Illinois Weather
Decatur weather this week
Over the next 7 days in Decatur, daytime highs range from 9°C to 19°C and night-time lows from -5°C to 8°C. The warmest afternoon is likely on Friday at 19°C, while the coolest night is expected tomorrow night at -5°C. Temperatures trend warmer through the week, rising by about 8°C. Expect a wide gap of around 12°C between afternoon and early-morning temperatures, so mornings will feel noticeably cooler.
No significant rain is expected in Decatur this week. The highest rain chance is just 4%, on Thursday.
Winds stay mostly light this week, peaking at about 29 km/h on Thursday. UV levels stay moderate or lower, peaking at 3. Average humidity is a comfortable 57% or so.
| Day | Conditions | High / Low | Rain chance | Rain | Max wind |
|---|---|---|---|---|---|
| Today (Saturday) | Clear sky | 9° / -4° | 0% | 0.0 mm | 15 km/h |
| Tomorrow (Sunday) | Overcast | 10° / -5° | 0% | 0.0 mm | 7 km/h |
| Monday | Overcast | 11° / -3° | 0% | 0.0 mm | 12 km/h |
| Tuesday | Mainly clear | 14° / 3° | 0% | 0.0 mm | 16 km/h |
| Wednesday | Overcast | 16° / 4° | 0% | 0.0 mm | 29 km/h |
| Thursday | Overcast | 19° / 8° | 4% | 0.0 mm | 29 km/h |
| Friday | Overcast | 19° / 7° | 3% | 0.0 mm | 17 km/h |
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Today's outlook for Decatur
At 23:00 local time it is 0°C in Decatur under clear skies, feeling like -4°C. Today's forecast high is 9°C and the low is -4°C, and the day overall looks clear and sunny. Rain is unlikely today (0% chance). Winds are blowing at about 6 km/h from the north. Humidity is 73%.
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Climate of Decatur: monthly averages
Based on 25 years of satellite and reanalysis data (2001-2025), July is usually the hottest month in Decatur, with average daytime highs around 29°C. January is the coolest, when nights typically fall to about -8°C and frost is possible on the coldest nights. That is a wide yearly range of roughly 37°C, so the seasons feel very different from each other.
The area receives about 1020 mm of rain in a typical year. Most of it falls from April to June, and June is the wettest month at roughly 120 mm.
For outdoor plans and travel, July to October usually offer the most comfortable weather in Decatur, with mild days and relatively little rain.
| Month | Avg high | Avg low | Rainfall | Humidity |
|---|---|---|---|---|
| Jan | 1° | -8° | 57 mm | 84% |
| Feb | 3° | -7° | 56 mm | 82% |
| Mar | 11° | -1° | 70 mm | 79% |
| Apr | 18° | 5° | 104 mm | 75% |
| May | 23° | 12° | 115 mm | 77% |
| Jun | 28° | 17° | 120 mm | 77% |
| Jul | 29° | 19° | 99 mm | 76% |
| Aug | 29° | 18° | 84 mm | 73% |
| Sep | 26° | 14° | 82 mm | 71% |
| Oct | 18° | 6° | 94 mm | 72% |
| Nov | 11° | 0° | 71 mm | 77% |
| Dec | 4° | -5° | 64 mm | 84% |
Source: NASA POWER (MERRA-2 reanalysis), averaged over the roughly 50 km grid area around Decatur. Values describe typical conditions, not a forecast.
About Decatur weather
Decatur is a place in Illinois's humid continental climate, shaped by its Great Lakes and prairie geography, located about 60 km east of Springfield. Decatur gets warm, humid summers (June–August) each year. Decatur closes out the year with cold winters (December–February) with regular snow, colder near Lake Michigan. This page shows live, auto-refreshing weather for Decatur: current conditions, an hourly breakdown, a 16-day outlook, a date-lookup tool for any past or future date, and real-time air quality, sourced from Open-Meteo. Local timezone: America/Chicago.
Frequently asked questions
Decatur is about 60 km east of Springfield, in Illinois.
Decatur sees cold winters (December–February) with regular snow, colder near Lake Michigan.
The live current conditions, hourly forecast and 16-day outlook above are pulled in real time for Decatur's exact coordinates. No fixed schedule, the page updates whenever you load it.
July is usually the hottest month in Decatur, with average daytime highs of about 29°C and nights around 19°C.
The coldest nights come in January, when the average low is about -8°C and daytime highs reach around 1°C. Frost is possible on clear, calm nights.
Decatur receives about 1020 mm of rain in a typical year. June is the wettest month at roughly 120 mm, and the main rainy period is April to June.
July to October usually offer the most comfortable weather in Decatur, with mild daytime temperatures and little rain.
In November Decatur typically sees daytime highs near 11°C and lows near 0°C, with about 71 mm of rain over the month and average humidity around 77%. Check the live forecast above for this week's actual conditions.
Up to 16 days ahead using the extended forecast and date picker above; further-out or historical dates use the same date lookup tool.
The current temperature for Decatur updates automatically at the top of this page — scroll to the hourly strip below to see how it's expected to change over the day.
Decatur's day-to-day weather follows the broader pattern of Illinois described above. See the hourly weather forecast or the air quality index for more detail.