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September Weather in Riverside, United States

Last updated: June 24, 2025

In September, the average temperature in Riverside, United States hovers around 21°C (70°F), making it a comfortable destination. Expect a range from a brisk 5°C (42°F) to a warm 34°C (94°F). During this month, precipitation amounts to about 88 mm (3.5 in) over 8 days, and the average humidity stands at 73%, ensuring a pleasantly humid atmosphere.

September Temperature in Riverside

In September in Riverside, the average temperature is 21°C (70°F), with maximums reaching up to 34°C (94°F) and minimums dropping as low as 5°C (42°F). This makes it an ideal time for travelers who enjoy warm weather but should also be prepared for cooler evenings.

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 (70°F), with highs reaching up to 34°C (94°F) and lows dropping to around 5°C (42°F).
JanFebMarAprMayJunJulAugSepOctNovDec313543526472767469584237
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 88 mm (3.5 in) over the course of 8 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 88 mm (3.5 inches) of precipitation spread over approximately 8 days.
JanFebMarAprMayJunJulAugSepOctNovDec771051111051221271068188949597
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 73%. With an average temperature of 21°C (70°F), this humidity feels like a warm embrace that can make outdoor activities feel sweltering, so it's essential to stay hydrated and take breaks in the shade while exploring.

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 73%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec88%88%87%85%81%82%81%73%73%78%89%87%
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.
JanFebMarAprMayJunJulAugSepOctNovDec356910101098643
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 Weather0°C (31°F)77 mm (3.0 inches)88%moderate
February Weather1°C (35°F)105 mm (4.1 inches)88%moderate
March Weather6°C (43°F)111 mm (4.4 inches)87%high
April Weather11°C (53°F)105 mm (4.1 inches)85%very high
May Weather18°C (65°F)122 mm (4.8 inches)81%very high
June Weather22°C (73°F)127 mm (5.0 inches)82%very high
July Weather25°C (77°F)106 mm (4.2 inches)81%very high
August Weather23°C (74°F)81 mm (3.2 inches)73%very high
September Weather21°C (70°F)88 mm (3.5 inches)73%very high
October Weather14°C (58°F)94 mm (3.7 inches)78%high
November Weather6°C (42°F)94 mm (3.7 inches)89%moderate
December Weather3°C (37°F)97 mm (3.8 inches)87%moderate

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