Weather on December 18
Simi Valley, CA
55 Years of Data
Avg High
64°F
Avg Low
50°F
Warmest
2025
75°F avg
Coldest
2008
45°F avg
About This Date
December 18th in Simi Valley, CA typically brings mild winter weather, with average highs around 64°F and lows near 50°F. Over 31 years of records, the warmest December 18th was in 2025 (75°F average), while the coldest was 2008 (45°F) — a 30°F range across recorded history. This date has historically been dry, with little recorded precipitation. The last decade has been 1.9°F warmer on this date compared to 20-30 years ago.
The last decade has been 1.9°F warmer on this date compared to 20-30 years ago.
Planning for December 18th in Simi Valley, CA? Great weather for outdoor activities.
Warming Trend
2.1°F per decade on this date
| Year | High | Low | Avg | Precip | Snow |
|---|---|---|---|---|---|
| 2025warmest | 83° | 68° | 75° | — | — |
| 2024 | 79° | 66° | 72° | — | — |
| 2023 | 67° | 54° | 60° | — | — |
| 2022 | 62° | 47° | 54° | — | — |
| 2021 | 66° | 50° | 58° | — | — |
| 2020 | 64° | 50° | 57° | — | — |
| 2019 | 60° | 47° | 53° | — | — |
| 2018 | 66° | 51° | 59° | — | — |
| 2017 | 70° | 52° | 61° | — | — |
| 2016 | 55° | 42° | 49° | — | — |
| 2015 | 70° | 52° | 61° | — | — |
| 2014 | 56° | 48° | 52° | — | — |
| 2013 | 70° | 48° | 59° | — | — |
| 2012 | 55° | 39° | 47° | — | — |
| 2011 | 59° | 45° | 52° | — | — |
| 2010 | 57° | 55° | 56° | — | — |
| 2009 | 74° | 59° | 66° | — | — |
| 2008coldest | 54° | 36° | 45° | — | — |
| 2007 | 55° | 50° | 53° | — | — |
| 2006 | 54° | 45° | 49° | — | — |
| 2005 | 59° | 48° | 54° | — | — |
| 2004 | 75° | 63° | 69° | — | — |
| 2003 | 75° | 63° | 69° | — | — |
| 2002 | 57° | 36° | 46° | — | — |
| 2001 | 63° | 39° | 51° | — | — |
| 2000 | 68° | 56° | 62° | — | — |
| 1999 | 80° | 61° | 70° | — | — |
| 1998 | 57° | 49° | 53° | — | — |
| 1997 | 54° | 46° | 50° | — | — |
| 1996 | 61° | 49° | 55° | — | — |
| 1995 | 61° | 46° | 53° | — | — |
31 years of data from SIMI VALLEY CALIFORNIA