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September Weather in Riverside, United States

Last updated: June 24, 2025

In September, the average temperature in Riverside, United States is a pleasant 19°C (67°F). You can expect temperatures to range from a cool 2°C (36°F) to a warm 33°C (92°F). This month also sees an average precipitation of 115 mm (4.5 in) spread over 9 days, contributing to an average humidity level of 66%. Enjoy the varying weather!

September Temperature in Riverside

In September in Riverside, the average temperature is 19°C (67°F), with maximums reaching 33°C (92°F) and minimums dropping as low as 2°C (36°F). This range makes it a great time to visit for those who enjoy mild weather but should be prepared for both warm days and cooler nights.

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 33°C (92°F) and lows dropping to around 2°C (36°F).
JanFebMarAprMayJunJulAugSepOctNovDec303340506170767467574235
Data source: Temperature data for Riverside generated using information from the Copernicus Climate Change Service.
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The average of daily temperatures (24 hours) calculated across all days in the month.

September Precipitation in Riverside

In Riverside in September, the precipitation amount is 115 mm (4.5 in) over the course of 9 days, indicating a relatively wet period for the region.

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 115 mm (4.5 inches) of precipitation spread over approximately 9 days.
JanFebMarAprMayJunJulAugSepOctNovDec719889106124891281181151209488
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Riverside

In Riverside in September humidity is 66%. With an average temperature of 19°C (67°F), this humidity feels like a warm blanket wrapping around you, making it mildly uncomfortable for traveling, as you may find yourself needing to frequently stop for hydration and to seek shade from the sun.

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 66%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec87%85%85%83%75%74%65%62%66%79%87%85%
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.
JanFebMarAprMayJunJulAugSepOctNovDec356910101098642
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.
 TemperaturePrecipitationHumidityUV
January Weather-1°C (31°F)71 mm (2.8 inches)87%moderate
February Weather1°C (33°F)98 mm (3.9 inches)85%moderate
March Weather4°C (40°F)89 mm (3.5 inches)85%high
April Weather10°C (51°F)106 mm (4.2 inches)83%very high
May Weather16°C (62°F)124 mm (4.9 inches)75%very high
June Weather21°C (70°F)89 mm (3.5 inches)73%very high
July Weather24°C (76°F)128 mm (5.0 inches)65%very high
August Weather23°C (74°F)118 mm (4.6 inches)62%very high
September Weather19°C (67°F)115 mm (4.5 inches)66%very high
October Weather14°C (57°F)120 mm (4.7 inches)79%high
November Weather5°C (42°F)94 mm (3.7 inches)87%moderate
December Weather2°C (35°F)88 mm (3.5 inches)85%low

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