The official National Weather Service forecast for Garrison — 47.6522°N, 101.4157°W, 58.6 miles from I-94.
| McLean County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 21 | 24 | 37 | 53 | 66 | 76 | 83 | 82 | 73 | 55 | 39 | 25 | 53 |
| Avg low °F | 3 | 5 | 17 | 29 | 41 | 52 | 57 | 55 | 46 | 33 | 20 | 8 | 30 |
| Precip in | 0.4 | 0.5 | 0.7 | 1.3 | 2.7 | 3.3 | 2.4 | 2.1 | 1.7 | 1.3 | 0.6 | 0.7 | 17.7 |
1996–2025 normals for McLean County — the climate division Garrison sits in. All-time county record high 104.5°F (1978-09-06); record low -37.9°F (1983-12-23). Source: NOAA / National Weather Service.