The official National Weather Service forecast for Castine — 39.9317°N, 84.6244°W, 9.9 miles from I-70.
| Darke County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 35 | 39 | 50 | 63 | 73 | 81 | 84 | 83 | 78 | 65 | 51 | 40 | 62 |
| Avg low °F | 20 | 22 | 31 | 40 | 51 | 60 | 63 | 61 | 54 | 43 | 33 | 25 | 42 |
| Precip in | 2.9 | 2.4 | 3.5 | 4.1 | 4.3 | 4.5 | 4.0 | 3.4 | 3.1 | 2.9 | 2.8 | 3.0 | 40.9 |
1996–2025 normals for Darke County — the climate division Castine sits in. All-time county record high 103.0°F (2012-06-29); record low -26.4°F (1994-01-19). Source: NOAA / National Weather Service.