The official National Weather Service forecast for Fullerton — 33.8703°N, 117.9253°W, 2.6 miles from I-5. Forecasts here are written by NWS SGX, this county’s forecast office.
| Orange County | J | F | M | A | M | J | J | A | S | O | N | D | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg high °F | 68 | 67 | 69 | 72 | 74 | 78 | 84 | 86 | 84 | 79 | 73 | 67 | 75 |
| Avg low °F | 47 | 47 | 49 | 51 | 55 | 59 | 63 | 64 | 62 | 57 | 51 | 47 | 54 |
| Precip in | 2.4 | 3.1 | 1.7 | 0.7 | 0.3 | 0.0 | 0.0 | 0.0 | 0.1 | 0.5 | 1.1 | 2.3 | 12.2 |
1996–2025 normals for Orange County — the climate division Fullerton sits in. All-time county record high 109.3°F (2018-07-07); record low 30.6°F (1968-12-22). Source: NOAA / National Weather Service.