September weather forecast
Mill Valley, CA

Share

Weather in September

The first month of the autumn, September, is still a pleasant month in Mill Valley, California, with an average temperature varying between 56.1°F (13.4°C) and 72.3°F (22.4°C).

Temperature

Temperature readings reach their annual highs in September, averaging 72.3°F (22.4°C) and a minimum average of 56.1°F (13.4°C).

Humidity

In September, the average relative humidity is 71%.

Rainfall

June through September are months with the least rain in Mill Valley when the rain falls for 1.7 days and typically aggregates up to 0.04" (1mm) of rain.

Daylight

The average length of the day in September is 12h and 25min.
On the first day of September, sunrise is at 6:40 am and sunset at 7:38 pm. On the last day of the month, sunrise is at 7:05 am and sunset at 6:54 pm PDT.

Sunshine

The average sunshine in September is 10.4h.

UV index

The months with the highest UV index are April, June through September, with an average maximum UV index of 5. A UV Index value of 3 to 5 symbolizes a medium vulnerability from unsafe exposure to UV radiation for the ordinary person.
Note: In September, an average UV index of 5 transforms into the following instructions:
Act with care - The suggestion to avoid sunburn is emphasized. Being exposed to the midday Sun can have harmful effects due to strong UV radiation; always take precautions. Employ a hat with a wide brim for robust protection, cutting UV exposure by half.
Updated: Jul 16, 2024
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate

Frequently asked questions

What time of the year is the hottest?

Mill Valley's warmest month, September, generally records average temperatures ranging from a high of 72.3°F (22.4°C) to a low of 56.1°F (13.4°C).

What is the usual temperature for Mill Valley in September?

In Mill Valley, 72.3°F (22.4°C) is the average high-temperature and 56.1°F (13.4°C) is the average low-temperature during September.

What is the average humidity in September?

In Mill Valley, the average relative humidity in September is 71%.

What is the driest month in Mill Valley?

The months with the least rainfall are June through September Rain falls for 1.7 days and accumulates 0.04" (1mm) of rain.

How many days does it rain in September?

In September, the rain falls for 1.7 days. Throughout September, 0.04" (1mm) of precipitation is accumulated.

How many hours of daylight does Mill Valley have in September?

The average day length in September is 12h and 25min.

When are sunrise and sunset in September in Mill Valley?

On the first day of September, sunrise is at 6:40 am and sunset at 7:38 pm. On the last day of the month, sunrise is at 7:05 am and sunset at 6:54 pm PDT.

How long on average sun shines in September?

In Mill Valley, the average sunshine duration in September is 10.4h.

What is the month with the highest UV index?

April, June through September, with an average maximum UV index of 5, are months with the highest UV index.

What is the UV index reading in September?

The average daily maximum UV index in September is 5. A UV Index reading of 3 to 5 represents a moderate vulnerability from exposure to the Sun's UV radiation.
Average humidity
Average rainfall days
Average daylight
Average sunshine
Average sunshine days
Average UV index
Average cloud cover
Average visibility

Average temperature in September
Mill Valley, CA

Average temperature in September - Mill Valley, CA
  • Average high temperature in September: 72.3°F

The warmest month (with the highest average high temperature) is September (72.3°F).
The month with the lowest average high temperature is December (55.4°F).

  • Average low temperature in September: 56.1°F

The month with the highest average low temperature is September (56.1°F).
The coldest month (with the lowest average low temperature) is December (45.3°F).

Average pressure in September
Mill Valley, CA

Average pressure in September - Mill Valley, CA
  • Average pressure in September: 29.92"Hg

The month with the highest atmospheric pressure is January (30.13"Hg).
The months with the lowest atmospheric pressure are June, August and September (29.92"Hg).

Average wind speed in September
Mill Valley, CA

Average wind speed in September - Mill Valley, CA
  • Average wind speed in September: 5.9mph

The windiest month (with the highest average wind speed) is May (7.8mph).
The calmest months (with the lowest average wind speed) are October and November (5.5mph).

Average humidity in September
Mill Valley, CA

Average humidity in September - Mill Valley, CA
  • Average humidity in September: 71%

The month with the highest relative humidity is March (77%).
The month with the lowest relative humidity is October (68%).

Average rainfall in September
Mill Valley, CA

Average rainfall in September - Mill Valley, CA
  • Average rainfall in September: 0.04"

The wettest month (with the highest rainfall) is February (0.87").
The driest months (with the least rainfall) are June, July, August and September (0.04").

Average rainfall days in September
Mill Valley, CA

Average rainfall days in September - Mill Valley, CA
  • Average rainfall days in September: 1.7 days

The month with the highest number of rainy days is March (8.8 days).
The months with the least rainy days are June and August (1.2 days).

Average daylight in September /
Average sunshine in September
Mill Valley, CA

Average daylight in September / Average sunshine in September - Mill Valley, CA
  • Average daylight in September: 12h and 2min

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: 10h and 2min

The month with the most sunshine is July (Average sunshine: 11h and 12min).
The month with the least sunshine is December (Average sunshine: 5h and 30min).

Average sunshine days in September
Mill Valley, CA

Average sunshine days in September - Mill Valley, CA
  • Average sunshine days in September: 26 days

The month with the most sunshine days is June (26.4 days).
The month with the least sunshine days is March (20.7 days).

Average UV index in September
Mill Valley, CA

Average UV index in September - Mill Valley, CA
  • Average UV index in September: 5

The months with the highest UV index are April, June, July, August and September (UV index 5).
The months with the lowest UV index are January, February, November and December (UV index 3).

Average cloud cover in September
Mill Valley, CA

Average cloud cover in September - Mill Valley, CA
  • Average cloud cover in September: 19

The month with the most cloud cover is March (Cloud cover 39).
The month with the least cloud cover is September (Cloud cover 19).

Average visibility in September
Mill Valley, CA

Average visibility in September - Mill Valley, 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).

Mill Valley, California, USA

Weather forecast for your location

1. Click Locate me button
2. Allow the app to use your location