September Weather in Riverside, United States

Last updated: June 24, 2025

In Riverside, United States, the average temperature in September hovers around 19°C (67°F). Temperatures can range from a chilly 3°C (37°F) to a sweltering 36°C (97°F). Expect about 34 mm (1.3 in) of precipitation spread over 4 days, and enjoy an average humidity level of 46%.

September Temperature in Riverside

In September in Riverside, the average temperature is 19°C (67°F). Maximums can reach 36°C (97°F), and minimums can drop as low as 3°C (37°F). Be prepared for a wide range of temperatures when traveling during this time.

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 19°C (67°F), with highs reaching up to 36°C (97°F) and lows dropping to around 3°C (37°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 34 mm (1.3 in) over a span of 4 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 34 mm (1.3 inches) of precipitation spread over approximately 4 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 46%. With an average temperature of 19°C (67°F), this humidity feels like a comfortable embrace, making it pleasant for traveling and exploring, though a light jacket might be advisable for the evening chill.

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 46%, 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 9, which corresponds to a very high Exposure Category. The time to burn is just 15 minutes, so it's essential to take precautions. For detailed information, you can check 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 9, 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	-3°C (27°F)	53 mm (2.1 inches)	91%	moderate
February Weather	0°C (31°F)	63 mm (2.5 inches)	92%	moderate
March Weather	5°C (42°F)	58 mm (2.3 inches)	84%	high
April Weather	10°C (49°F)	60 mm (2.4 inches)	74%	very high
May Weather	15°C (59°F)	44 mm (1.7 inches)	62%	very high
June Weather	22°C (71°F)	19 mm (0.7 inches)	56%	extreme
July Weather	27°C (80°F)	12 mm (0.5 inches)	44%	extreme
August Weather	25°C (77°F)	16 mm (0.6 inches)	37%	very high
September Weather	19°C (67°F)	34 mm (1.3 inches)	46%	very high
October Weather	10°C (50°F)	41 mm (1.6 inches)	67%	high
November Weather	4°C (39°F)	38 mm (1.5 inches)	84%	moderate
December Weather	-2°C (28°F)	42 mm (1.7 inches)	88%	moderate