O'Fallon, Missouri vs Decatur, Illinois Climate
97%matchO'Fallon and Decatur are a 97% climate match. Very close: temperatures within 2°F (1°C), with similar rain, humidity and sun.
O'Fallon gets 39 in (998 mm) of rain a year and Decatur 41 in (1034 mm). July is the warmest month in both, with highs of 90°F (32°C) in O'Fallon and 88°F (31°C) in Decatur.
Climate fingerprints: ring color = average temperature, thickness = rain. January at the top.
Month by month
Highs and lows (°F)
O'FallonDecatursolid = high, dashed = low
Rain (in per month)
O'FallonDecatur
Monthly averages
| Month | High | Low | Rain | |||
|---|---|---|---|---|---|---|
| O'Fallon | Decatur | O'Fallon | Decatur | O'Fallon | Decatur | |
| Jan | 40°F(5°C) | 37°F(3°C) | 22°F(-6°C) | 20°F(-7°C) | 2.0 in(50 mm) | 2.2 in(55 mm) |
| Feb | 46°F(8°C) | 41°F(5°C) | 25°F(-4°C) | 23°F(-5°C) | 2.0 in(52 mm) | 2.0 in(51 mm) |
| Mar | 57°F(14°C) | 53°F(12°C) | 34°F(1°C) | 33°F(1°C) | 3.2 in(81 mm) | 3.0 in(75 mm) |
| Apr | 69°F(20°C) | 65°F(19°C) | 44°F(7°C) | 43°F(6°C) | 3.9 in(98 mm) | 4.1 in(105 mm) |
| May | 78°F(26°C) | 76°F(25°C) | 55°F(13°C) | 53°F(12°C) | 4.8 in(121 mm) | 4.9 in(125 mm) |
| Jun | 86°F(30°C) | 85°F(29°C) | 64°F(18°C) | 62°F(17°C) | 3.7 in(95 mm) | 4.6 in(118 mm) |
| Jul | 90°F(32°C) | 88°F(31°C) | 68°F(20°C) | 66°F(19°C) | 4.3 in(108 mm) | 4.3 in(110 mm) |
| Aug | 89°F(32°C) | 87°F(30°C) | 66°F(19°C) | 64°F(18°C) | 3.3 in(84 mm) | 3.4 in(86 mm) |
| Sep | 82°F(28°C) | 81°F(27°C) | 57°F(14°C) | 56°F(13°C) | 3.5 in(88 mm) | 3.3 in(83 mm) |
| Oct | 70°F(21°C) | 68°F(20°C) | 45°F(7°C) | 45°F(7°C) | 3.1 in(80 mm) | 3.0 in(77 mm) |
| Nov | 56°F(13°C) | 53°F(12°C) | 35°F(2°C) | 34°F(1°C) | 3.1 in(79 mm) | 3.1 in(80 mm) |
| Dec | 44°F(7°C) | 41°F(5°C) | 26°F(-3°C) | 25°F(-4°C) | 2.4 in(62 mm) | 2.7 in(69 mm) |
1991–2020 averages, by calendar month.