The official National Weather Service forecast for Roundup — 46.4452°N, 108.5418°W, 39.6 miles from I-94.
| Musselshell County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 36 | 37 | 48 | 57 | 66 | 77 | 87 | 86 | 75 | 59 | 46 | 37 | 59 |
| Avg low °F | 14 | 15 | 23 | 31 | 40 | 49 | 56 | 53 | 45 | 33 | 23 | 15 | 33 |
| Precip in | 0.5 | 0.5 | 0.7 | 1.6 | 2.9 | 2.7 | 1.3 | 1.2 | 1.2 | 1.2 | 0.5 | 0.5 | 14.8 |
1996–2025 normals for Musselshell County — the climate division Roundup sits in. All-time county record high 109.9°F (2026-07-13); record low -37.6°F (2024-01-14). Source: NOAA / National Weather Service.