The official National Weather Service forecast for Fairmont — 39.4851°N, 80.1426°W, population 31,694, 4.8 miles from I-79.
| Marion County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 39 | 44 | 53 | 65 | 74 | 81 | 84 | 83 | 77 | 66 | 54 | 44 | 64 |
| Avg low °F | 22 | 25 | 31 | 40 | 49 | 57 | 62 | 61 | 54 | 43 | 33 | 27 | 42 |
| Precip in | 3.6 | 3.3 | 3.6 | 3.9 | 4.8 | 4.8 | 4.9 | 3.9 | 3.5 | 3.3 | 2.9 | 3.5 | 46.0 |
1996–2025 normals for Marion County — the climate division Fairmont sits in. All-time county record high 100.0°F (1988-07-17); record low -22.8°F (1994-01-19). Source: NOAA / National Weather Service.