Climate averages 1991–2020
Riverside weather
in September.
A hot, very dry month: the 3rd warmest and the 4th driest of the year.
Long-term climate patterns, not a forecast for a particular trip.
September is a hot month in Riverside: daytime highs average 32.0°C and nights cool to about 17.5°C. By daytime temperature it is the 3rd warmest of the 12 months.
Expect about 5.5 mm of rain on roughly 1 day, which makes September a very dry month (the 4th driest of the 12 months). Daylight, from sunrise to sunset, lasts about 12 h 25 min on an average September day.
The nearest other city in this atlas is Moreno Valley (15 km away). In September its highs average 30.8°C, 1.1°C cooler than Riverside, with 7.8 mm of rain.
Among the 498 cities listed in the United States, Riverside ranks joint 28th of 498 for the warmest September highs and joint 90th of 498 for the driest September (rainfall, lowest first). The mean September high of those 498 cities is 26.9°C; Riverside is 5.1°C warmer than that mean.
From September to October, average highs fall by 5.1°C to 26.9°C, and monthly rainfall rises from 5.5 mm to 22 mm.
The annual picture
September 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
Riverside climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 17.4°C4.7°C | 4.7°C | 96 | 6.6 | 10.210 h |
| February | 17.8°C5.7°C | 5.7°C | 111 | 7.4 | 10.911 h |
| March | 19.8°C7.5°C | 7.5°C | 68 | 6.8 | 12.012 h |
| April | 22.4°C9.5°C | 9.5°C | 32 | 4.6 | 13.013 h |
| May | 25.2°C12.3°C | 12.3°C | 15 | 2.6 | 13.914 h |
| June | 29.3°C15.4°C | 15.4°C | 3.4 | 0.5 | 14.414 h |
| July | 32.7°C18.9°C | 18.9°C | 2.2 | 0.5 | 14.214 h |
| August | 33.8°C19.7°C | 19.7°C | 1.1 | 0.3 | 13.413 h |
| September, selected | 32.0°C17.5°C | 17.5°C | 5.5 | 1.2 | 12.412 h |
| October | 26.9°C12.7°C | 12.7°C | 22 | 3.1 | 11.411 h |
| November | 21.6°C8.0°C | 8.0°C | 30 | 3.5 | 10.410 h |
| December | 17.1°C4.5°C | 4.5°C | 67 | 5.8 | 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
September in nearby cities
- Moreno Valley in SeptemberUnited States · 15 kmHigh 30.8°C · Low 17.2°C · 7.8 mm rain
- Fontana in SeptemberUnited States · 16 kmHigh 31.6°C · Low 17.0°C · 5.5 mm rain
- Corona in SeptemberUnited States · 18 kmHigh 31.6°C · Low 17.8°C · 5.5 mm rain
- San Bernardino in SeptemberUnited States · 20 kmHigh 31.9°C · Low 17.5°C · 7.8 mm rain
- Redlands in SeptemberUnited States · 23 kmHigh 32.0°C · Low 17.7°C · 7.8 mm rain
- Perris in SeptemberUnited States · 24 kmHigh 30.7°C · Low 17.3°C · 6.0 mm rain
- Rancho Cucamonga in SeptemberUnited States · 25 kmHigh 31.4°C · Low 17.4°C · 5.5 mm rain
- Ontario in SeptemberUnited States · 26 kmHigh 31.1°C · Low 17.7°C · 4.3 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 Riverside) is explained once on the Riverside year overview and on the Sources, method and limits page.
Fontana, Rancho Cucamonga and Corona lie in the same rainfall cell, so their rainfall figures are identical to these; temperatures differ because they come from smaller 0.1° cells.