The official National Weather Service forecast for Petersburg — 38.9926°N, 79.1239°W, 30.5 miles from I-81.
| Grant County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 39 | 44 | 52 | 64 | 72 | 80 | 83 | 82 | 76 | 64 | 53 | 43 | 63 |
| Avg low °F | 21 | 23 | 29 | 38 | 47 | 55 | 59 | 58 | 51 | 41 | 31 | 25 | 40 |
| Precip in | 2.9 | 2.7 | 3.1 | 3.5 | 4.7 | 4.3 | 3.8 | 3.8 | 3.9 | 3.2 | 2.5 | 2.8 | 41.2 |
1996–2025 normals for Grant County — the climate division Petersburg sits in. All-time county record high 99.3°F (1988-07-17); record low -18.1°F (1985-01-21). Source: NOAA / National Weather Service.