The official National Weather Service forecast for Big Timber — 45.8349°N, 109.9555°W, 1.3 miles from I-90.
| Sweet Grass County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 35 | 35 | 44 | 51 | 61 | 70 | 81 | 79 | 70 | 55 | 43 | 35 | 55 |
| Avg low °F | 17 | 15 | 22 | 28 | 36 | 44 | 51 | 49 | 42 | 32 | 23 | 17 | 31 |
| Precip in | 0.9 | 1.1 | 1.3 | 2.0 | 3.2 | 2.7 | 1.3 | 1.3 | 1.5 | 1.7 | 1.1 | 1.1 | 19.2 |
1996–2025 normals for Sweet Grass County — the climate division Big Timber sits in. All-time county record high 103.2°F (2026-07-13); record low -35.8°F (1983-12-24). Source: NOAA / National Weather Service.