The official National Weather Service forecast for Newcastle — 37.6666°N, 113.5494°W, 20.9 miles from I-15. Forecasts here are written by NWS SLC, this county’s forecast office.
| Iron County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 42 | 45 | 53 | 60 | 70 | 82 | 88 | 85 | 78 | 65 | 52 | 42 | 64 |
| Avg low °F | 19 | 22 | 27 | 32 | 40 | 49 | 57 | 55 | 47 | 36 | 26 | 19 | 36 |
| Precip in | 1.2 | 1.4 | 1.4 | 1.1 | 0.9 | 0.4 | 1.3 | 1.5 | 1.2 | 1.4 | 1.0 | 1.3 | 14.1 |
1996–2025 normals for Iron County — the climate division Newcastle sits in. All-time county record high 100.1°F (2002-07-14); record low -19.3°F (1990-12-23). Source: NOAA / National Weather Service.