The official National Weather Service forecast for Onawa — 42.0266°N, 96.0972°W, 3.6 miles from I-29.
| Monona County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 30 | 35 | 49 | 62 | 72 | 83 | 86 | 83 | 78 | 64 | 49 | 35 | 60 |
| Avg low °F | 12 | 15 | 27 | 37 | 49 | 60 | 64 | 61 | 53 | 40 | 27 | 16 | 38 |
| Precip in | 0.7 | 0.8 | 1.7 | 3.1 | 4.6 | 4.2 | 3.4 | 4.0 | 2.8 | 2.2 | 1.3 | 1.1 | 29.9 |
1996–2025 normals for Monona County — the climate division Onawa sits in. All-time county record high 104.1°F (1955-07-31); record low -26.5°F (2021-02-16). Source: NOAA / National Weather Service.