September Weather in Walnut Creek, United States

Last updated: June 24, 2025

In Walnut Creek, United States, the average temperature in September is a pleasant 24°C (75°F). During this time, temperatures can vary, with a minimum of 9°C (49°F) and a maximum reaching up to 35°C (96°F). Visitors should be prepared for some rain, as the average precipitation is 148 mm (5.8 in) over 11 days, contributing to an average humidity of 79%.

September Temperature in Walnut Creek

In September in Walnut Creek, the average temperature is 24°C (75°F), with maximums reaching up to 35°C (96°F) and minimums dipping as low as 9°C (49°F). This variability makes it an ideal destination for travelers seeking a warm climate with the option for cooler evenings.

September Weather in Walnut Creek: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Walnut Creek, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Walnut Creek, September typically has an average temperature of 24°C (75°F), with highs reaching up to 35°C (96°F) and lows dropping to around 9°C (49°F).

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

September Precipitation in Walnut Creek

In Walnut Creek in September, the precipitation amount is 148 mm (5.8 in) spread over a duration of 11 days.

September Precipitation Trends in Walnut Creek

The chart displays monthly precipitation patterns in Walnut Creek, 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 Walnut Creek, September typically receives around 148 mm (5.8 inches) of precipitation spread over approximately 11 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 Walnut Creek

In Walnut Creek in September, humidity is 79%. With an average temperature of 24°C (75°F), this humidity feels like a warm, tropical embrace, making traveling quite sticky and requiring ample hydration and light clothing to keep comfortable while exploring.

September Average Humidity in Walnut Creek

This chart illustrates the average monthly humidity levels in Walnut Creek, 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 Walnut Creek is approximately 79%, 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 Walnut Creek

In Walnut Creek 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 Walnut Creek.

Maximum UV Index Levels in Walnut Creek for September

The chart shows the monthly maximum UV Index (UVI) for Walnut Creek 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 Walnut Creek typically reaches 9, which falls under the very high exposure category.

Data source: Walnut Creek 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 Walnut Creek Compares to Other Months

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

This table compares monthly weather conditions in Walnut Creek, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
	Temperature	Precipitation	Humidity	UV
January Weather	7°C (45°F)	88 mm (3.5 inches)	85%	moderate
February Weather	10°C (51°F)	85 mm (3.3 inches)	82%	high
March Weather	12°C (54°F)	72 mm (2.8 inches)	81%	very high
April Weather	17°C (63°F)	104 mm (4.1 inches)	80%	very high
May Weather	22°C (71°F)	115 mm (4.5 inches)	81%	extreme
June Weather	25°C (77°F)	139 mm (5.5 inches)	81%	extreme
July Weather	27°C (81°F)	127 mm (5.0 inches)	81%	extreme
August Weather	26°C (79°F)	159 mm (6.3 inches)	80%	very high
September Weather	24°C (75°F)	148 mm (5.8 inches)	79%	very high
October Weather	19°C (67°F)	65 mm (2.5 inches)	80%	very high
November Weather	12°C (53°F)	88 mm (3.5 inches)	85%	moderate
December Weather	9°C (49°F)	107 mm (4.2 inches)	86%	moderate