Climate averages 1991–2020
Simi Valley weather
in December.
A mild, moderately wet month: the coolest and the 9th driest of the year.
Long-term climate patterns, not a forecast for a particular trip.
December is a mild month in Simi Valley: daytime highs average 17.4°C and nights cool to about 5.9°C. By daytime temperature it is the coolest month of the year.
Expect about 58 mm of rain on roughly 5 days, which makes December a moderately wet month (the 9th driest of the 12 months). Daylight, from sunrise to sunset, lasts about 9 h 55 min on an average December day.
The nearest other city in this atlas is Thousand Oaks (12 km away). In December its highs average 17.4°C, about as warm as Simi Valley, with 58 mm of rain.
Among the 498 cities listed in the United States, Simi Valley ranks joint 90th of 498 for the warmest December highs and joint 200th of 498 for the driest December (rainfall, lowest first). The mean December high of those 498 cities is 10.5°C; Simi Valley is 6.9°C warmer than that mean.
From December to January, average highs rise by 0.3°C to 17.7°C, and monthly rainfall rises from 58 mm to 91 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
Simi Valley climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 17.7°C6.0°C | 6.0°C | 91 | 5.6 | 10.110 h |
| February | 17.8°C6.4°C | 6.4°C | 98 | 6.4 | 10.911 h |
| March | 19.5°C7.9°C | 7.9°C | 66 | 5.6 | 11.912 h |
| April | 21.7°C9.7°C | 9.7°C | 22 | 2.9 | 13.013 h |
| May | 23.9°C12.7°C | 12.7°C | 12 | 1.8 | 13.914 h |
| June | 26.8°C15.6°C | 15.6°C | 2.0 | 0.5 | 14.414 h |
| July | 29.6°C18.7°C | 18.7°C | 3.1 | 0.5 | 14.214 h |
| August | 30.7°C19.3°C | 19.3°C | 0.3 | 0.1 | 13.413 h |
| September | 29.5°C17.6°C | 17.6°C | 3.9 | 0.6 | 12.412 h |
| October | 25.8°C13.7°C | 13.7°C | 20 | 2.1 | 11.411 h |
| November | 21.5°C9.2°C | 9.2°C | 21 | 2.6 | 10.410 h |
| December, selected | 17.4°C5.9°C | 5.9°C | 58 | 4.8 | 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
- Thousand Oaks in DecemberUnited States · 12 kmHigh 17.4°C · Low 6.5°C · 58 mm rain
- Valencia, United States in DecemberUnited States · 25 kmHigh 17.0°C · Low 4.8°C · 50 mm rain
- Santa Clarita in DecemberUnited States · 26 kmHigh 16.5°C · Low 4.7°C · 50 mm rain
- Oxnard in DecemberUnited States · 37 kmHigh 16.6°C · Low 9.1°C · 58 mm rain
- Burbank in DecemberUnited States · 45 kmHigh 18.4°C · Low 6.3°C · 58 mm rain
- Ventura in DecemberUnited States · 47 kmHigh 17.1°C · Low 7.5°C · 58 mm rain
- Glendale (California), United States in DecemberUnited States · 50 kmHigh 18.1°C · Low 6.3°C · 58 mm rain
- Inglewood in DecemberUnited States · 52 kmHigh 18.4°C · Low 6.7°C · 52 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 Simi Valley) is explained once on the Simi Valley year overview and on the Sources, method and limits page.
Thousand Oaks lies in the same rainfall cell, so its rainfall figures are identical to these; temperatures differ because they come from smaller 0.1° cells.