The official National Weather Service forecast for Newcastle — 43.8547°N, 104.2049°W, 35.6 miles from I-90.
| Weston County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 34 | 36 | 48 | 56 | 65 | 78 | 88 | 86 | 76 | 60 | 46 | 35 | 59 |
| Avg low °F | 11 | 12 | 22 | 29 | 39 | 49 | 57 | 54 | 45 | 31 | 21 | 12 | 32 |
| Precip in | 0.4 | 0.5 | 0.8 | 1.7 | 2.7 | 2.3 | 2.2 | 1.4 | 1.1 | 1.2 | 0.5 | 0.4 | 15.2 |
1996–2025 normals for Weston County — the climate division Newcastle sits in. All-time county record high 104.7°F (2006-07-16); record low -37.8°F (1990-12-22). Source: NOAA / National Weather Service.