Decatur, IL Weather & Climate Normals
What a normal year in Decatur actually looks like
On the 30-year record NOAA keeps for Decatur, IL, the comfort score comes out to 47/100, strongly seasonal: Comfortable weather is limited to a shorter window; summers, winters, or precipitation swing wide. Only 5 months a year land in the 55–75°F range this site treats as mild.
How much Decatur's weather actually swings
Average temperatures in Decatur run from 27°F in Jan up to 76°F in Jul, a 48.7°F seasonal swing, one of the widest gaps in this dataset.
Decatur, month by month
| Month | Avg high | Avg low | Precip | Snow |
|---|---|---|---|---|
| Jan | 34°F | 20°F | 2.4in | 5.9in |
| Feb | 39°F | 24°F | 2in | 2.5in |
| Mar | 51°F | 33°F | 2.64in | 0.9in |
| Apr | 63°F | 43°F | 4.12in | 0.4in |
| May | 74°F | 54°F | 4.95in | 0in |
| Jun | 82°F | 63°F | 4.73in | 0in |
| Jul | 85°F | 67°F | 4in | 0in |
| Aug | 84°F | 65°F | 3.5in | 0in |
| Sep | 78°F | 57°F | 3.08in | 0in |
| Oct | 65°F | 46°F | 3.41in | 0in |
| Nov | 50°F | 34°F | 3.21in | 0.4in |
| Dec | 39°F | 25°F | 2.4in | 3.5in |
If you're timing a visit, May, Jun, Aug, Sep, and Oct are Decatur's mildest stretch; if you're moving there, you should plan around Jul's heat and Jan's cold instead.
How wet Decatur actually gets
Over a typical year, Decatur sees about 40.44in of precipitation a year across roughly 116 days with measurable rain or snow, with 13.6in of snow a year.
Decatur against the rest of the country
Out of 4876 cities scored here, Decatur comes in at 2552; within IL alone it ranks 83 of 330. Population is about 68,763.
Checking the actual forecast
These figures come from Decatur Wtp, IL US, the NOAA station 2.1 miles from Decatur, averaged over 30 years, not tomorrow's forecast.
More on how this is worked out
Why some cities show no snow or rain figure · What a 30-year climate normal actually is