nomadseason

September Weather in Walnut Creek, United States

Last updated: June 24, 2025

In Walnut Creek, United States, the average temperature in September hovers around 20°C (69°F), offering a pleasant climate. Expect a range where the minimum dips to 8°C (47°F), while the mercury can soar to a sizzling 42°C (107°F). With a meager precipitation of just 1 mm (0.0 in) over 0 days, enjoy low humidity levels at 55%, making it an ideal time to explore the outdoors!

September Temperature in Walnut Creek

In September in Walnut Creek, the average temperature is 20°C (69°F). The maximum can reach 42°C (107°F), while the minimum can drop to as low as 8°C (47°F). This variety in temperatures makes Walnut Creek an ideal destination for travelers seeking both warm days and 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 20°C (69°F), with highs reaching up to 42°C (107°F) and lows dropping to around 8°C (47°F).
JanFebMarAprMayJunJulAugSepOctNovDec505255596368686968645650
Data source: Temperature data for Walnut Creek generated using information from the Copernicus Climate Change Service.
Choose your preferred temperature unit
The average of daily temperatures (24 hours) calculated across all days in the month.

September Precipitation in Walnut Creek

In Walnut Creek in September, the precipitation amount is 1 mm (0.0 in) during a span of 0 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 1 mm (0.0 inches) of precipitation spread over approximately 0 days.
JanFebMarAprMayJunJulAugSepOctNovDec99897231161001233775
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
Choose your preferred precipitation unit

September Humidity in Walnut Creek

In Walnut Creek in September humidity is 55%. With an average temperature of 20°C (69°F), this humidity feels like a refreshing embrace, making it ideal for exploring the local sights while still requiring a light layer to stay comfortable.

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 55%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec82%84%82%78%71%64%59%54%55%62%78%80%
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.
JanFebMarAprMayJunJulAugSepOctNovDec3589101111109643
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.
 TemperaturePrecipitationHumidityUV
January Weather10°C (50°F)99 mm (3.9 inches)82%moderate
February Weather11°C (53°F)89 mm (3.5 inches)84%moderate
March Weather13°C (55°F)72 mm (2.8 inches)82%very high
April Weather15°C (59°F)31 mm (1.2 inches)78%very high
May Weather17°C (63°F)16 mm (0.6 inches)71%very high
June Weather20°C (68°F)1 mm (0.1 inches)64%extreme
July Weather20°C (68°F)0 mm (0.0 inches)58%extreme
August Weather20°C (69°F)0 mm (0.0 inches)54%very high
September Weather20°C (69°F)1 mm (0.0 inches)55%very high
October Weather18°C (64°F)23 mm (0.9 inches)62%high
November Weather13°C (56°F)37 mm (1.5 inches)78%moderate
December Weather10°C (50°F)75 mm (2.9 inches)80%moderate

Compare Walnut Creek's Climate with Cities Worldwide