September weather forecastWalnut Creek, CA

Vast fields and forest slopes of the iconic Mount Diablo State Park within the Walnut Creek in California

September

Weather in September

The first month of the autumn, September, is also a moderately hot month in Walnut Creek, California, with an average temperature fluctuating between 57.2°F (14°C) and 81.5°F (27.5°C).

Temperature

The advent of September denotes an average high-temperature of a still moderately hot 81.5°F (27.5°C), subtly different from August's 81.7°F (27.6°C). The nighttime temperature shows a significant divergence from the daytime highs, averaging at a refreshing 57.2°F (14°C) in September.

Heat index

For most parts of September, the heat index is calculated to be 84.2°F (29°C). Long-standing exposure and activity could induce a feeling of tiredness and lead to heat cramps.
Heat index evaluations are typically in the context of light winds and shaded environments. In the presence of direct sunshine, the heat index could be augmented by 15 Fahrenheit (8 Celsius) degrees.
Note: The heat index, also known as 'real feel' or 'apparent temperature', blends air temperature and moisture content to represent the felt temperature to humans. The individual's impression of temperature can be shaped by additional aspects such as metabolic variations, physical activity, and clothing. Recognize that direct exposure to the sun can escalate the heat effect, potentially adding 15 Fahrenheit (8 Celsius) degrees to the heat index. Heat index values are especially crucial for babies and toddlers. Kids frequently fail to realize the necessity for resting and hydrating. Thirst is an advanced indication of dehydration - hence, maintaining hydration, especially during extended physical activities, becomes essential.

Humidity

The months with the lowest humidity in Walnut Creek are September and October, with an average relative humidity of 58%.

Rainfall

In September, the rain falls for 2.3 days. Throughout September, 0.08" (2mm) of precipitation is accumulated. In Walnut Creek, during the entire year, the rain falls for 68.7 days and collects up to 11.26" (286mm) of precipitation.

Daylight

The average length of the day in September is 12h and 25min.
On the first day of September in Walnut Creek, sunrise is at 6:38 am and sunset at 7:37 pm. On the last day of the month, sunrise is at 7:03 am and sunset at 6:52 pm PDT.

Sunshine

In Walnut Creek, the average sunshine in September is 11.1h.

UV index

In September, the average daily maximum UV index in Walnut Creek is 5. A UV Index of 3 to 5 symbolizes a medium vulnerability from unprotected exposure to Sun's UV rays for average individuals.
Note: The maximum UV index, 5 during September, leads to the following recommendations:
Be mindful. Those with pale skin might receive burns in fewer than 30 minutes. Midday is the peak time for the Sun's radiation; stay in the shade and protect yourself. A wide-brimmed hat provides unparalleled sun protection for sensitive areas like the eyes, ears, and neck.

Updated: Feb 9, 2024
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate

Frequently asked questions

In Walnut Creek, in September, the average high-temperature is 81.5°F (27.5°C), and the average low-temperature is 57.2°F (14°C). In September, the average heat index (a.k.a. 'felt air temperature', 'real feel'), which combines air temperature and relative humidity, is calculated to be 84.2°F (29°C).

The months with the lowest humidity in Walnut Creek, California, are September and October, with an average relative humidity of 58%.

The average relative humidity in September in Walnut Creek is 58%.

In September, in Walnut Creek, the rain falls for 2.3 days. Throughout September, 0.08" (2mm) of precipitation is accumulated.

In September, the average day length is 12h and 25min.

In September, on the first day of the month, sunrise is at 6:38 am and sunset at 7:37 pm. On the last day of the month, in Walnut Creek, sunrise is at 7:03 am and sunset at 6:52 pm PDT.

In Walnut Creek, California, the average sunshine duration in September is 11.1h.

In September, the average daily maximum UV index is 5. A UV Index estimate of 3 to 5 represents a medium health risk from unprotected exposure to UV radiation.

Today

Tomorrow

Long-term

Year J F M A M J J A September O N D

Aug

September

Oct

Average high temperature

81.7°F

81.5°F

74.1°F

Average low temperature

Average pressure

Average wind speed

Average max. wind speed

6.9mph

6mph

5.5mph

Average wind speed gusts

Average humidity

Average rainfall

Average rainfall days

Average daylight

Average sunshine

Average sunshine days

29.6

27.5

25.8

Average UV index

Average cloud cover

Average visibility

Average temperature in September
Walnut Creek, CA

Average high temperature in September: 81.5°F

The warmest month (with the highest average high temperature) is July (82.8°F).
The month with the lowest average high temperature is December (55.4°F).

Average low temperature in September: 57.2°F

The month with the highest average low temperature is September (57.2°F).
The coldest months (with the lowest average low temperature) are January and December (42.4°F).

Average pressure in September
Walnut Creek, CA

Average pressure in September: 29.92"Hg

The month with the highest atmospheric pressure is January (30.14"Hg).
The month with the lowest atmospheric pressure is June (29.91"Hg).

Average wind speed in September
Walnut Creek, CA

Average wind speed in September: 5.7mph

The windiest month (with the highest average wind speed) is May (7.3mph).
The calmest month (with the lowest average wind speed) is November (4.4mph).

Average humidity in September
Walnut Creek, CA

Average humidity in September: 58%

The month with the highest relative humidity is March (74%).
The months with the lowest relative humidity are September and October (58%).

Average rainfall in September
Walnut Creek, CA

Average rainfall in September: 0.08"

The wettest month (with the highest rainfall) is February (2.4").
The driest months (with the least rainfall) are July and August (0.04").

Average rainfall days in September
Walnut Creek, CA

Average rainfall days in September: 2.3 days

The month with the highest number of rainy days is March (12.6 days).
The month with the least rainy days is August (0.8 days).

Average daylight in September /
Average sunshine in September
Walnut Creek, CA

Average daylight in September: 12h and 24min

The month with the longest days is June (Average daylight: 14h and 48min).
The month with the shortest days is December (Average daylight: 9h and 36min).

Average sunshine in September: 11h and 6min

The month with the most sunshine is July (Average sunshine: 12h and 0min).
The month with the least sunshine is December (Average sunshine: 5h and 48min).

Average sunshine days in September
Walnut Creek, CA

Average sunshine days in September: 27.5 days

The month with the most sunshine days is August (29.6 days).
The month with the least sunshine days is March (17.5 days).

Average UV index in September
Walnut Creek, CA

Average UV index in September: 5

The months with the highest UV index are June and July (UV index 6).
The months with the lowest UV index are January, February, November and December (UV index 3).

Average cloud cover in September
Walnut Creek, CA

Average cloud cover in September: 11

The month with the most cloud cover is March (Cloud cover 36).
The month with the least cloud cover is July (Cloud cover 8).

Average visibility in September
Walnut Creek, CA

Average visibility in September: 6mi

The months with the highest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
The months with the lowest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).