September Weather in Riverside, United States

Last updated: June 24, 2025

In September, the average temperature in Riverside, United States hovers around 21°C (71°F). Expect a temperature range that can dip to a chilly 6°C (43°F) and rise to a scorching 35°C (95°F). Prepare for some rain, as 105 mm (4.1 in) of precipitation typically falls over 10 days, while the average humidity sits at a comfortable 75%. Enjoy the diverse climate this month has to offer!

September Temperature in Riverside

In September in Riverside, the average temperature is 21°C (71°F). Maximum temperatures can reach 35°C (95°F), while minimums can drop as low as 6°C (43°F). Overall, it's a great time to explore Riverside with warm days and cooler nights, perfect for outdoor adventures.

September Weather in Riverside: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Riverside, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Riverside, September typically has an average temperature of 21°C (71°F), with highs reaching up to 35°C (95°F) and lows dropping to around 6°C (43°F).

Data source: Temperature data for Riverside generated using information from the Copernicus Climate Change Service.

September Precipitation in Riverside

In Riverside in September, the precipitation amount is 105 mm (4.1 in) over the course of 10 days.

September Precipitation Trends in Riverside

The chart displays monthly precipitation patterns in Riverside, with values for each month alongside September’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how September’s conditions compare to those of other months. In Riverside, September typically receives around 105 mm (4.1 inches) of precipitation spread over approximately 10 days.

Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.

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Millimeters (mm) Inches (in)

September Humidity in Riverside

In Riverside in September, humidity is 75%. With an average temperature of 21°C (71°F), this humidity feels like a warm blanket wrapping around you, making travel slightly uncomfortable but offering a lush, vibrant atmosphere that invites exploration at a leisurely pace.

September Average Humidity in Riverside

This chart illustrates the average monthly humidity levels in Riverside, with September’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In September, average humidity in Riverside is approximately 75%, offering insight into how humid the weather typically is during this month.

Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Riverside

In Riverside in September, the maximum UV index is 8, which corresponds to a very high Exposure Category. This means that the time to burn is only 15 minutes. For more detailed information, you can refer to the Hourly UV Index in Riverside.

Maximum UV Index Levels in Riverside for September

The chart shows the monthly maximum UV Index (UVI) for Riverside in September, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues. In September, the maximum UV index in Riverside typically reaches 8, which falls under the very high exposure category.

Data source: Riverside September UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

Extreme (11+): Avoid the sun, stay in shade.
Very High (8-10): Limit sun exposure.
High (6-7): Use SPF 30+ and protective clothing.
Moderate (3-5): Midday shade recommended.
Low (0-2): No protection needed.

How September Weather in Riverside Compares to Other Months

Weather in Riverside varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Riverside, focusing on differences in temperature, rainfall, humidity, and UV levels.

This table compares monthly weather conditions in Riverside, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
	Temperature	Precipitation	Humidity	UV
January Weather	2°C (36°F)	60 mm (2.4 inches)	84%	moderate
February Weather	4°C (40°F)	99 mm (3.9 inches)	83%	moderate
March Weather	7°C (45°F)	89 mm (3.5 inches)	83%	high
April Weather	13°C (56°F)	94 mm (3.7 inches)	81%	very high
May Weather	18°C (65°F)	139 mm (5.5 inches)	78%	very high
June Weather	23°C (74°F)	133 mm (5.2 inches)	79%	very high
July Weather	26°C (80°F)	168 mm (6.6 inches)	74%	very high
August Weather	25°C (77°F)	148 mm (5.8 inches)	72%	very high
September Weather	21°C (71°F)	105 mm (4.1 inches)	75%	very high
October Weather	16°C (61°F)	106 mm (4.2 inches)	81%	high
November Weather	8°C (47°F)	84 mm (3.3 inches)	85%	moderate
December Weather	4°C (40°F)	95 mm (3.7 inches)	84%	moderate