The official National Weather Service forecast for Grinnell — 41.743°N, 92.7224°W, population 9,486, 4 miles from I-80.
| Poweshiek County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 29 | 34 | 48 | 61 | 71 | 81 | 84 | 82 | 77 | 64 | 48 | 35 | 60 |
| Avg low °F | 12 | 16 | 27 | 38 | 49 | 60 | 63 | 60 | 53 | 41 | 29 | 18 | 39 |
| Precip in | 1.1 | 1.2 | 2.1 | 3.4 | 5.0 | 5.5 | 4.2 | 4.0 | 3.2 | 3.2 | 1.9 | 1.5 | 36.3 |
1996–2025 normals for Poweshiek County — the climate division Grinnell sits in. All-time county record high 103.0°F (2012-07-26); record low -29.3°F (1996-02-03). Source: NOAA / National Weather Service.