The official National Weather Service forecast for Ontario — 34.0633°N, 117.6509°W, 1.7 miles from I-10. Forecasts here are written by NWS VEF, this county’s forecast office.
| San Bernardino County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 60 | 63 | 70 | 77 | 86 | 96 | 102 | 100 | 93 | 81 | 68 | 59 | 80 |
| Avg low °F | 39 | 41 | 46 | 51 | 59 | 68 | 75 | 73 | 67 | 55 | 45 | 38 | 55 |
| Precip in | 1.0 | 1.2 | 0.6 | 0.3 | 0.1 | 0.0 | 0.3 | 0.4 | 0.3 | 0.3 | 0.5 | 0.9 | 5.9 |
1996–2025 normals for San Bernardino County — the climate division Ontario sits in. All-time county record high 113.4°F (2024-07-09); record low 15.9°F (1990-12-23). Source: NOAA / National Weather Service.