Weather on August 21
Simi Valley, CA
55 Years of Data
Avg High
88°F
Avg Low
62°F
Warmest
2025
89°F avg
Coldest
2002
62°F avg
About This Date
August 21st in Simi Valley, CA typically brings warm summer weather, with average highs around 88°F and lows near 62°F — a 26°F daily swing. Over 30 years of records, the warmest August 21st was in 2025 (89°F average), while the coldest was 2002 (62°F) — a 27°F range across recorded history. This date has historically been dry, with little recorded precipitation. The last decade has been 4.6°F warmer on this date compared to 20-30 years ago.
The last decade has been 4.6°F warmer on this date compared to 20-30 years ago.
Planning for August 21st in Simi Valley, CA? Stay hydrated and seek shade during peak afternoon hours.
Warming Trend
1.5°F per decade on this date
| Year | High | Low | Avg | Precip | Snow |
|---|---|---|---|---|---|
| 2025warmest | 105° | 74° | 89° | — | — |
| 2024 | 98° | 67° | 82° | — | — |
| 2023 | 79° | 59° | 69° | — | — |
| 2022 | 90° | 61° | 75° | — | — |
| 2021 | 78° | 59° | 69° | — | — |
| 2020 | 101° | 72° | 86° | — | — |
| 2019 | 98° | 71° | 85° | — | — |
| 2018 | 89° | 63° | 76° | — | — |
| 2017 | 90° | 59° | 74° | — | — |
| 2016 | 93° | 66° | 80° | — | — |
| 2015 | 83° | 59° | 71° | — | — |
| 2014 | 90° | 61° | 75° | — | — |
| 2013 | 95° | 67° | 81° | — | — |
| 2012 | 84° | 63° | 73° | — | — |
| 2011 | 77° | 54° | 65° | — | — |
| 2010 | 84° | 59° | 72° | — | — |
| 2009 | 83° | 59° | 71° | — | — |
| 2008 | 81° | 61° | 71° | — | — |
| 2007 | 86° | 66° | 76° | — | — |
| 2006 | 81° | 55° | 68° | — | — |
| 2005 | 84° | 54° | 69° | — | — |
| 2004 | 73° | 59° | 66° | — | — |
| 2003 | 79° | 61° | 70° | — | — |
| 2002coldest | 70° | 55° | 62° | — | — |
| 2001 | 81° | 56° | 68° | — | — |
| 2000 | 89° | 59° | 74° | — | — |
| 1999 | 98° | 65° | 81° | — | — |
| 1998 | 100° | 70° | 85° | — | — |
| 1997 | 95° | 70° | 82° | — | — |
| 1996 | 100° | 65° | 82° | — | — |
30 years of data from SIMI VALLEY CALIFORNIA