Decatur, IL Weather OverviewScoresFors & AgainstsWeatherPhotos Average Temperature Jan 32 °F0 °C Feb 35 °F2 °C Mar 45 °F7 °C Apr 57 °F14 °C May 72 °F22 °C Jun 77 °F25 °C Jul 84 °F29 °C Aug 81 °F27 °C Sep 80 °F27 °C Oct 63 °F17 °C Nov 41 °F5 °C Dec 41 °F5 °C Humidity Jan 77% Feb 76% Mar 68% Apr 71% May 78% Jun 81% Jul 82% Aug 82% Sep 80% Oct 71% Nov 76% Dec 78% Rain Jan 75mm Feb 58mm Mar 94mm Apr 88mm May 172mm Jun 173mm Jul 47mm Aug 184mm Sep 91mm Oct 87mm Nov 41mm Dec 53mm Clouds Jan 66% Feb 70% Mar 54% Apr 60% May 57% Jun 47% Jul 26% Aug 31% Sep 33% Oct 31% Nov 56% Dec 56% Air quality US AQI Jan 38 Feb 37 Mar 35 Apr 36 May 38 Jun 34 Jul 38 Aug 39 Sep 36 Oct 32 Nov 42 Dec 45 Sun Jan 2UVI Feb 3UVI Mar 4UVI Apr 5UVI May 7UVI Jun 8UVI Jul 9UVI Aug 7UVI Sep 7UVI Oct 4UVI Nov 2UVI Dec 2UVI
