The official National Weather Service forecast for Hermosa — 43.8397°N, 103.191°W, 18 miles from I-90.
| Custer County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 37 | 38 | 48 | 56 | 65 | 77 | 85 | 84 | 75 | 60 | 47 | 38 | 59 |
| Avg low °F | 14 | 14 | 23 | 30 | 40 | 51 | 58 | 55 | 46 | 34 | 23 | 15 | 34 |
| Precip in | 0.4 | 0.6 | 1.0 | 2.1 | 3.3 | 2.9 | 2.7 | 2.0 | 1.4 | 1.3 | 0.5 | 0.5 | 18.7 |
1996–2025 normals for Custer County — the climate division Hermosa sits in. All-time county record high 104.4°F (2006-07-16); record low -32.2°F (1983-12-23). Source: NOAA / National Weather Service.