September weather in Riverside, WA
The average temperature in Riverside in September is 63.3°F (48.4°F–78.2°F). Average precipitation: 0.40 inches.
September is a fall month in Riverside, and is warmer than the annual average of 49.9°F. Daily temperatures swing about 29.8°F between overnight low and afternoon high. Expect about 4 days with precipitation. Daylight averages about 12h 20m. For travel, September is a comfortable month to visit.
Avg High
78.2°F
Avg Low
48.4°F
Precipitation
0.40 in
Daylight
12h 20m
September records in Riverside
| Date | Record High | Record Low | Record Precip |
|---|---|---|---|
| September 1 | 100.0°F (2024) | 36.0°F (2006) | 0.01 in (2001) |
| September 2 | 100.9°F (2025) | 37.9°F (2006) | 0.37 in (2014) |
| September 3 | 104.0°F (2025) | 39.0°F (2015) | 0.03 in (2009) |
| September 4 | 102.0°F (2025) | 35.1°F (2011) | 0.26 in (2013) |
| September 5 | 99.0°F (2020) | 41.0°F (2011) | 0.24 in (2009) |
| September 6 | 96.1°F (1998) | 39.0°F (2000) | 0.25 in (2013) |
| September 7 | 96.1°F (2024) | 37.0°F (1999) | 0.13 in (2010) |
| September 8 | 96.1°F (2011) | 33.1°F (2002) | 0.48 in (2019) |
| September 9 | 99.0°F (2011) | 33.1°F (2000) | 0.47 in (2019) |
| September 10 | 98.1°F (2011) | 39.0°F (2003) | 0.24 in (2021) |
| September 11 | 98.1°F (2011) | 33.1°F (2014) | 0.06 in (2004) |
| September 12 | 93.9°F (2011) | 31.1°F (2014) | 0.05 in (2005) |
| September 13 | 97.0°F (2013) | 34.0°F (2012) | 0.09 in (2022) |
| September 14 | 93.9°F (2013) | 41.0°F (2012) | 0.14 in (2022) |
| September 15 | 91.9°F (2001) | 41.0°F (2012) | 0.27 in (2013) |
| September 16 | 91.0°F (2001) | 35.1°F (2011) | 0.07 in (2003) |
| September 17 | 91.0°F (2008) | 32.0°F (2006) | 0.33 in (2019) |
| September 18 | 89.1°F (2008) | 39.0°F (2005) | 1.03 in (2019) |
| September 19 | 91.0°F (2012) | 37.0°F (2017) | 0.53 in (2010) |
| September 20 | 87.1°F (1999) | 36.0°F (2004) | 0.86 in (2023) |
| September 21 | 89.1°F (2014) | 33.1°F (2004) | 0.08 in (2008) |
| September 22 | 87.1°F (1999) | 30.0°F (2000) | 0.12 in (2013) |
| September 23 | 90.0°F (2009) | 21.9°F (2000) | 0.26 in (2020) |
| September 24 | 90.0°F (2011) | 26.1°F (2000) | 0.11 in (2014) |
| September 25 | 90.0°F (2003) | 30.0°F (2000) | 0.26 in (2014) |
| September 26 | 87.1°F (2003) | 30.9°F (2000) | 0.22 in (2001) |
| September 27 | 89.1°F (2022) | 30.9°F (2000) | 0.42 in (2023) |
| September 28 | 87.1°F (2010) | 24.1°F (1999) | 0.32 in (2007) |
| September 29 | 84.0°F (2003) | 28.2°F (2007) | 0.08 in (2002) |
| September 30 | 82.9°F (2003) | 34.0°F (2011) | 0.71 in (2007) |