Climate averages 1991–2020
Rancho Cucamonga 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 Rancho Cucamonga: daytime highs average 31.4°C and nights cool to about 17.4°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 Ontario (7 km away). In September its highs average 31.1°C, about as warm as Rancho Cucamonga, with 4.3 mm of rain.
Among the 498 cities listed in the United States, Rancho Cucamonga ranks joint 42nd 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; Rancho Cucamonga is 4.5°C warmer than that mean.
From September to October, average highs fall by 4.9°C to 26.4°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
Rancho Cucamonga climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 17.2°C5.6°C | 5.6°C | 96 | 6.6 | 10.210 h |
| February | 17.5°C6.1°C | 6.1°C | 111 | 7.4 | 10.911 h |
| March | 19.5°C7.7°C | 7.7°C | 68 | 6.8 | 12.012 h |
| April | 22.0°C9.4°C | 9.4°C | 32 | 4.6 | 13.013 h |
| May | 24.8°C12.2°C | 12.2°C | 15 | 2.6 | 13.914 h |
| June | 28.9°C15.3°C | 15.3°C | 3.4 | 0.5 | 14.414 h |
| July | 32.3°C18.7°C | 18.7°C | 2.2 | 0.5 | 14.214 h |
| August | 33.3°C19.2°C | 19.2°C | 1.1 | 0.3 | 13.413 h |
| September, selected | 31.4°C17.4°C | 17.4°C | 5.5 | 1.2 | 12.412 h |
| October | 26.4°C13.2°C | 13.2°C | 22 | 3.1 | 11.411 h |
| November | 21.3°C8.8°C | 8.8°C | 30 | 3.5 | 10.410 h |
| December | 16.9°C5.4°C | 5.4°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
- Ontario in SeptemberUnited States · 7 kmHigh 31.1°C · Low 17.7°C · 4.3 mm rain
- Chino in SeptemberUnited States · 14 kmHigh 30.5°C · Low 17.4°C · 4.3 mm rain
- Fontana in SeptemberUnited States · 15 kmHigh 31.6°C · Low 17.0°C · 5.5 mm rain
- Pomona in SeptemberUnited States · 16 kmHigh 30.7°C · Low 17.3°C · 4.3 mm rain
- Chino Hills in SeptemberUnited States · 20 kmHigh 29.8°C · Low 17.1°C · 4.3 mm rain
- Riverside in SeptemberUnited States · 25 kmHigh 32.0°C · Low 17.5°C · 5.5 mm rain
- Corona in SeptemberUnited States · 26 kmHigh 31.6°C · Low 17.8°C · 5.5 mm rain
- San Bernardino in SeptemberUnited States · 28 kmHigh 31.9°C · Low 17.5°C · 7.8 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 Rancho Cucamonga) is explained once on the Rancho Cucamonga year overview and on the Sources, method and limits page.
Riverside, Fontana 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.