| Month | High | Low | Rain | Wet days | Score |
|---|---|---|---|---|---|
| January | 20.9° | 8° | 54.6mm | 5.3 | 89 |
| February | 20.8° | 8.6° | 67.7mm | 6.7 | 87 |
| March | 21.8° | 10.5° | 36.3mm | 5.6 | 89 |
| April | 23.2° | 12.1° | 15mm | 3.1 | 94 |
| May | 24.3° | 14.6° | 6.7mm | 1.8 | 96 |
| June | 26.4° | 16.8° | 0.7mm | 0.5 | 99 |
| July | 29.4° | 18.8° | 0.8mm | 0.3 | 90 |
| August | 30.5° | 19.1° | 2.2mm | 0.4 | 85 |
| September | 29.8° | 18° | 3.3mm | 0.8 | 87 |
| October | 27.1° | 14.7° | 12.9mm | 2.9 | 94 |
| November | 23.7° | 10.4° | 18.8mm | 4.2 | 92 |
| December | 20.2° | 7.7° | 48.2mm | 6.4 | 87 |
January in Fullerton averages a daily high of 20.9°C with nights around 8°C. Expect roughly 5.3 wet days totalling 54.6mm. Comfortable conditions for being outdoors all day.
February in Fullerton averages a daily high of 20.8°C with nights around 8.6°C. Expect roughly 6.7 wet days totalling 67.7mm. Comfortable conditions for being outdoors all day.
March in Fullerton averages a daily high of 21.8°C with nights around 10.5°C. Expect roughly 5.6 wet days totalling 36.3mm. Comfortable conditions for being outdoors all day.
April in Fullerton averages a daily high of 23.2°C with nights around 12.1°C. Expect roughly 3.1 wet days totalling 15mm. Comfortable conditions for being outdoors all day.
May in Fullerton averages a daily high of 24.3°C with nights around 14.6°C. Rain is rare — about 1.8 wet days and 6.7mm across the month. Comfortable conditions for being outdoors all day.
June in Fullerton averages a daily high of 26.4°C with nights around 16.8°C. Rain is rare — about 0.5 wet days and 0.7mm across the month. Comfortable conditions for being outdoors all day.
July in Fullerton averages a daily high of 29.4°C with nights around 18.8°C. Rain is rare — about 0.3 wet days and 0.8mm across the month. Comfortable conditions for being outdoors all day.
August in Fullerton averages a daily high of 30.5°C with nights around 19.1°C. Rain is rare — about 0.4 wet days and 2.2mm across the month. Comfortable conditions for being outdoors all day.
September in Fullerton averages a daily high of 29.8°C with nights around 18°C. Rain is rare — about 0.8 wet days and 3.3mm across the month. Comfortable conditions for being outdoors all day.
October in Fullerton averages a daily high of 27.1°C with nights around 14.7°C. Rain is rare — about 2.9 wet days and 12.9mm across the month. Comfortable conditions for being outdoors all day.
November in Fullerton averages a daily high of 23.7°C with nights around 10.4°C. Expect roughly 4.2 wet days totalling 18.8mm. Comfortable conditions for being outdoors all day.
December in Fullerton averages a daily high of 20.2°C with nights around 7.7°C. Expect roughly 6.4 wet days totalling 48.2mm. Comfortable conditions for being outdoors all day.
Each month scores out of 100. It starts at 100 and loses points for daytime highs outside a 20–27°C band, for wet days, and for nights below 2°C. Nothing else is weighted in — no crowd data, no prices, no opinion. Fullerton peaks at 99.
Based on 30 years of records, April–June scores highest for comfort in Fullerton, balancing daytime temperature against rainfall.
August is the warmest, averaging a daily high of 30.5°C.
February is the wettest, averaging 67.7mm of rain across roughly 6.7 wet days.
December is the coolest month, with average daily highs around 20.2°C.