Climate averages 1991–2020
Fullerton weather
in December.
A mild, moderately wet month: the coolest and the 10th driest of the year. Meets the pleasant-weather rule
Long-term climate patterns, not a forecast for a particular trip.
December is a mild month in Fullerton: daytime highs average 18.4°C and nights cool to about 6.5°C. By daytime temperature it is the coolest month of the year.
Expect about 48 mm of rain on roughly 5 days, which makes December a moderately wet month (the 10th driest of the 12 months). Daylight, from sunrise to sunset, lasts about 9 h 57 min on an average December day.
The nearest other city in this atlas is Anaheim (4 km away). In December its highs average 17.9°C, about as warm as Fullerton, with 48 mm of rain.
Among the 498 cities listed in the United States, Fullerton ranks joint 48th of 498 for the warmest December highs and joint 122nd of 498 for the driest December (rainfall, lowest first). The mean December high of those 498 cities is 10.5°C; Fullerton is 7.8°C warmer than that mean.
From December to January, average highs rise by 0.2°C to 18.6°C, and monthly rainfall rises from 48 mm to 71 mm.
The annual picture
December in context
Monthly rainfall
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Fullerton climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 18.6°C6.7°C | 6.7°C | 71 | 5.2 | 10.210 h |
| February | 18.8°C7.5°C | 7.5°C | 79 | 6.1 | 10.911 h |
| March | 20.3°C9.3°C | 9.3°C | 46 | 5.1 | 12.012 h |
| April | 22.5°C10.9°C | 10.9°C | 18 | 2.6 | 13.013 h |
| May | 24.4°C13.4°C | 13.4°C | 7.4 | 1.5 | 13.914 h |
| June | 27.2°C15.6°C | 15.6°C | 1.8 | 0.3 | 14.414 h |
| July | 30.3°C18.1°C | 18.1°C | 1.3 | 0.4 | 14.214 h |
| August | 31.6°C18.7°C | 18.7°C | 0.4 | 0.1 | 13.413 h |
| September | 30.3°C17.8°C | 17.8°C | 3.6 | 0.5 | 12.412 h |
| October | 26.6°C14.4°C | 14.4°C | 14 | 1.9 | 11.411 h |
| November | 22.4°C10.0°C | 10.0°C | 19 | 2.4 | 10.410 h |
| December, selected | 18.4°C6.5°C | 6.5°C | 48 | 4.9 | 9.910 h |
Rainfall is the average of the 30 separate monthly totals. A rain day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
December in nearby cities
- Anaheim in DecemberUnited States · 4 kmHigh 17.9°C · Low 6.6°C · 48 mm rain
- Buena Park in DecemberUnited States · 7 kmHigh 18.5°C · Low 6.4°C · 48 mm rain
- Westminster (California), United States in DecemberUnited States · 14 kmHigh 17.9°C · Low 7.0°C · 48 mm rain
- Santa Ana, United States in DecemberUnited States · 15 kmHigh 17.4°C · Low 8.1°C · 55 mm rain
- Whittier in DecemberUnited States · 16 kmHigh 18.0°C · Low 5.7°C · 55 mm rain
- Chino Hills in DecemberUnited States · 21 kmHigh 16.9°C · Low 5.1°C · 62 mm rain
- Downey in DecemberUnited States · 21 kmHigh 18.3°C · Low 6.1°C · 52 mm rain
- West Covina in DecemberUnited States · 22 kmHigh 18.4°C · Low 6.4°C · 55 mm rain
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for Fullerton) is explained once on the Fullerton year overview and on the Sources, method and limits page.
Anaheim, Huntington Beach and Westminster (California), United States lie in the same rainfall cell, so their rainfall figures are identical to these; temperatures differ because they come from smaller 0.1° cells.