The official National Weather Service forecast for Grimes — 41.6883°N, 93.7911°W, 2.8 miles from I-80.
| Polk County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 30 | 35 | 49 | 62 | 72 | 82 | 85 | 83 | 78 | 64 | 49 | 36 | 60 |
| Avg low °F | 13 | 16 | 28 | 39 | 50 | 61 | 65 | 62 | 54 | 42 | 30 | 19 | 40 |
| Precip in | 0.9 | 1.1 | 2.0 | 3.6 | 5.1 | 5.2 | 4.1 | 3.9 | 3.2 | 2.8 | 1.7 | 1.3 | 34.9 |
1996–2025 normals for Polk County — the climate division Grimes sits in. All-time county record high 103.9°F (1955-07-31); record low -28.1°F (1996-02-03). Source: NOAA / National Weather Service.