Mount Tomah boasts a year-around average temperature of 14.3°C, peaking at 21.7°C in January, its warmest month, and dipping to an average low of 6.9°C in July, the coolest. Rainfall averages at 61.1mm annually, with February seeing the heaviest showers and June being the driest month.
Month | Temperature (Celcius) | Rainfall (mm) |
| January | 21.7 | 81.3 |
| February | 21.1 | 88.9 |
| March | 18.3 | 69.8 |
| April | 13.9 | 45.7 |
| May | 11.2 | 45.7 |
| June | 8.0 | 34.3 |
| July | 6.9 | 36.8 |
| August | 8.5 | 45.7 |
| September | 11.2 | 45.7 |
| October | 14.0 | 69.8 |
| November | 17.1 | 87.6 |
| December | 20.2 | 81.3 |