September weather forecast and climate
Grass Valley, CA

Weather in September

The first month of the autumn, September, is still a warm month in Grass Valley, California, with temperature in the range of an average high of 83.8°F (28.8°C) and an average low of 56.5°F (13.6°C).

Temperature

In Grass Valley, the average high-temperature marginally drops, from a hot 89.2°F (31.8°C) in August, to a warm 83.8°F (28.8°C). The average low-temperature, in Grass Valley, is 56.5°F (13.6°C).

Heat index

In September, the average heat index is calculated to 83.1°F (28.4°C). Exhaustion is likely with prolonged exposure and activity. Sustaining activity may result in heat cramps.
Take into consideration that the heat index values are calculated for shade and light wind conditions. Exposure to direct sunshine can increase heat index values by up to 15 Fahrenheit (8 Celsius) degrees.
Note: The heat index, also known as 'feels like', 'real feel', 'apparent temperature', or 'felt air temperature', is a measure of how hot it feels when the actual air humidity is factored in. This effect is subjective, depending on the activity and individual's heat perception influenced by various reasons (metabolic differences, pregnancy, clothing). Bear in mind that direct sunshine exposure increases weather impact, and may raise heat index by up to 15 Fahrenheit (8 Celsius) degrees. Heat index values are especially crucial for babies and toddlers. Young children are generally more endangered than adults, as they usually less sweat. And also, due to larger skin surface relative to their small bodies and higher heat production as a result of their activity.

Humidity

The average relative humidity in September is 40%.

Rainfall

In Grass Valley, during 2.3 rainfall days, 0.28" (7mm) of precipitation is typically accumulated. In Grass Valley, during the entire year, the rain falls for 82 days and collects up to 33.11" (841mm) of precipitation.

Snowfall

In Grass Valley snow does not fall in June through October.

Daylight

The average length of the day in Grass Valley is 12.4h.

Sunshine

The average sunshine in September is 11.2h.

UV index

In Grass Valley, the average daily maximum UV index is 5. A UV Index of 3 to 5 symbolizes a medium health hazard from unprotected exposure to the Sun's UV rays for the ordinary person.
Note: The daily maximum UV index of 5 interpret into the following advice:
Take precautions - Protection against sun damage is advised. The Sun's most intense and consequently most harmful UV radiation during midday hours should be decreased by minimizing exposure and seeking shade. Sun-protective clothing, a long-sleeved shirt and pants, a wide-brimmed hat, and UVA and UVB-blocking sunglasses are particularly helpful in blocking UV radiation's harmful effects.
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FAQ

What is the temperature in September in Grass Valley?

In September, the average high-temperature is 83.8°F (28.8°C), and the average low-temperature is 56.5°F (13.6°C). The average heat index (a.k.a. 'felt air temperature', 'apparent temperature'), that combines relative humidity and air temperature, in September is calculated to 83.1°F (28.4°C).

What is the average humidity in September in Grass Valley?

In Grass Valley, California, the average relative humidity in September is 40%.

How much does it rain in Grass Valley in September?

In September, the rain falls for 2.3 days. Throughout September, 0.28" (7mm) of precipitation is accumulated.

When it does not snow in Grass Valley?

In Grass Valley snow does not fall in June through October.

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

The average length of the day in September is 12.4h.

How many hours of sunshine does Grass Valley have in September?

The average sunshine in September is 11.2h.

What is the UV index intensity in September in Grass Valley?

The average daily maximum UV index in September in Grass Valley is 5. A UV Index of 3 to 5 symbolizes a medium health risk from the exposure to the Sun's UV radiation.

Average temperature in September
Grass Valley, CA

Average temperature in September - Grass Valley, CA
  • Average high temperature in September: 83.8°F

The warmest month (with the highest average high temperature) is July (90.1°F).
The month with the lowest average high temperature is December (51.3°F).

  • Average low temperature in September: 56.5°F

The month with the highest average low temperature is July (60.1°F).
The coldest month (with the lowest average low temperature) is December (37.2°F).

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Average pressure in September
Grass Valley, CA

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

The month with the highest atmospheric pressure is January (30.17").
The month with the lowest atmospheric pressure is June (29.9").

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Average wind speed in September
Grass Valley, CA

Average wind speed in September - Grass Valley, CA
  • Average wind speed in September: 5.2mph

The windiest month (with the highest average wind speed) is February (6mph).
The calmest month (with the lowest average wind speed) is August (4.8mph).

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Average humidity in September
Grass Valley, CA

Average humidity in September - Grass Valley, CA
  • Average humidity in September: 40%

The month with the highest relative humidity is March (75%).
The month with the lowest relative humidity is July (37%).

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Average rainfall in September
Grass Valley, CA

Average rainfall in September - Grass Valley, CA
  • Average rainfall in September: 0.28"

The wettest month (with the highest rainfall) is March (6.57").
The driest months (with the least rainfall) are July and August (0.04").

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Average rainfall days in September
Grass Valley, CA

Average rainfall days in September - Grass Valley, CA
  • Average rainfall days in September: 2.3 days

The month with the highest number of rainy days is March (15.1 days).
The month with the least rainy days is July (1.1 days).

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Average snowfall in September
Grass Valley, CA

Average snowfall in September - Grass Valley, CA
  • Average snowfall in September: 0"

The month with the highest snowfall is February (6.42").
Months with the least snowfall are June, July, August, September and October (0").

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Average snowfall days in September
Grass Valley, CA

Average snowfall days in September - Grass Valley, CA
  • Average snowfall days in September: 0 days

The month with the highest number of snowfall days is March (2.4 days).
Months with the least snowfall days are June, July, August, September and October (0 days).

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

Average daylight in September / Average sunshine in September - Grass Valley, CA
  • Average daylight in September: 12.4h

The month with the longest days is June (Average daylight: 14.9h).
The month with the shortest days is December (Average daylight: 9.5h).

  • Average sunshine in September: 11.2h

The month with the most sunshine is July (Average sunshine: 12.2h).
The month with the least sunshine is January (Average sunshine: 5.7h).

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Average sunshine days in September
Grass Valley, CA

Average sunshine days in September - Grass Valley, CA
  • Average sunshine days in September: 26.9 days

The month with the most sunshine days is July (29.8 days).
The month with the least sunshine days is March (14.8 days).

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Average UV index in September
Grass Valley, CA

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

The month with the highest UV index is July (UV index 7).
The month with the lowest UV index is November (UV index 2).

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Average cloud cover in September
Grass Valley, CA

Average cloud cover in September - Grass Valley, CA
  • Average cloud cover in September: 8

The month with the most cloud cover is March (Cloud cover 41).
The month with the least cloud cover is July (Cloud cover 4).

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Average visibility in September
Grass Valley, CA

Average visibility in September - Grass Valley, CA
  • Average visibility in September: 6mi

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

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