The official National Weather Service forecast for De Witt — 41.8234°N, 90.5382°W, 17 miles from I-80.
| Clinton County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 29 | 34 | 48 | 61 | 72 | 81 | 84 | 82 | 77 | 63 | 48 | 35 | 60 |
| Avg low °F | 14 | 17 | 29 | 39 | 50 | 60 | 64 | 61 | 54 | 42 | 30 | 19 | 40 |
| Precip in | 1.3 | 1.6 | 2.3 | 3.7 | 4.5 | 5.1 | 4.3 | 3.8 | 3.4 | 3.0 | 1.9 | 1.9 | 36.8 |
1996–2025 normals for Clinton County — the climate division De Witt sits in. All-time county record high 101.6°F (1988-08-18); record low -31.0°F (2009-01-16). Source: NOAA / National Weather Service.