Contents
- Weather in September
- Frequently asked questions
- Average temperature in September
- Average pressure in September
- Average wind speed in September
- Average humidity in September
- Average rainfall in September
- Average rainfall days in September
- Average daylight in September
- Average sunshine in September
- Average sunshine days in September
- Average UV index in September
- Average cloud cover in September
- Average visibility in September
Weather in September
Temperature
Yountville's weather in September indicates an average high-temperature of a moderately hot 84°F (28.9°C), nearly consistent with the 86.2°F (30.1°C) of August. Contrasted against daytime highs, Yountville records an average nighttime low of 55.2°F (12.9°C) in September.Heat index
The heat index for September is appraised at a tropical 86°F (30°C). If one continues to be active during enduring exposure, it could result in fatigue and heat cramps.Be informed that the heat index values are oriented around shady conditions and gentle breezes. Direct sunlight might lead to a heat index increase by up to 15 Fahrenheit (8 Celsius) degrees.
Note: The heat index, also known as 'real feel' or 'feels like', is a numerical representation of warmth when taking temperature and moisture levels into account. The influence of weather is personal, differing among individuals based on variations in body mass, stature, and the degree of physical exertion. Should you be directly under the sun, anticipate a possible increase in the heat index by up to 15 Fahrenheit (8 Celsius) degrees. Heat index values are highly critical to babies and toddlers. Children typically face more danger than adults as their sweat production is usually lower. Additionally, the bigger skin surface compared to their small size and the increased heat due to their activeness exacerbate the risk.
Humidity
With an average relative humidity of 54%, September is the least humid month.Rainfall
In Yountville, in September, during 2.1 rainfall days, 0.08" (2mm) of precipitation is typically accumulated. Throughout the year, there are 77.8 rainfall days, and 16.02" (407mm) of precipitation is accumulated.Daylight
The average length of the day in September is 12h and 25min.On the first day of the month, sunrise is at 6:39 am and sunset at 7:38 pm. On the last day of September, in Yountville, sunrise is at 7:05 am and sunset at 6:53 pm PDT.
Sunshine
In Yountville, the average sunshine in September is 11.1h.UV index
In Yountville, the average daily maximum UV index in September is 5. A UV Index value of 3 to 5 symbolizes a medium vulnerability from exposure to the Sun's UV radiation for average individuals.Note: In September, the UV index of 5 transforms into the following advice:
Undertake protective steps - Preventing sun damage is advised. Direct exposure to the Sun during its peak hours around mid-day should be minimized for safety. Experience reduced UV exposure by about half when donning a wide-brim hat.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
Is it hot during September?
What is the least humid month?
What is the average humidity in September in Yountville?
How much does it rain in September?
How many hours of daylight does Yountville have in September?
When are sunrise and sunset in September?
How long on average sun shines in September?
What is the UV index intensity in September?
Average temperature in September
Yountville, CA
- Average high temperature in September: 84°F
The warmest month (with the highest average high temperature) is July (86.5°F).
The month with the lowest average high temperature is December (54.5°F).
- Average low temperature in September: 55.2°F
The month with the highest average low temperature is August (55.4°F).
The coldest month (with the lowest average low temperature) is December (40.1°F).
Average pressure in September
Yountville, CA
- Average pressure in September: 29.92"Hg
The month with the highest atmospheric pressure is January (30.14"Hg).
The months with the lowest atmospheric pressure are June and August (29.91"Hg).
Average wind speed in September
Yountville, CA
- Average wind speed in September: 4.7mph
The windiest month (with the highest average wind speed) is May (6mph).
The calmest month (with the lowest average wind speed) is November (4.3mph).
Average humidity in September
Yountville, CA
- Average humidity in September: 54%
The month with the highest relative humidity is March (76%).
The month with the lowest relative humidity is September (54%).
Average rainfall in September
Yountville, CA
- Average rainfall in September: 0.08"
The wettest month (with the highest rainfall) is February (3.43").
The driest months (with the least rainfall) are July and August (0.04").
Average rainfall days in September
Yountville, CA
- Average rainfall days in September: 2.1 days
The month with the highest number of rainy days is March (13.9 days).
The month with the least rainy days is August (0.9 days).
Average daylight in September /
Average sunshine in September
Yountville, 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 30min).
- Average sunshine in September: 11h and 1min
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 36min).
Average sunshine days in September
Yountville, CA
- Average sunshine days in September: 26.9 days
The month with the most sunshine days is July (29.4 days).
The month with the least sunshine days is March (15.8 days).
Average UV index in September
Yountville, CA
- Average UV index in September: 5
The months with the highest UV index are June, July and August (UV index 6).
The months with the lowest UV index are January, February, November and December (UV index 3).
Average cloud cover in September
Yountville, CA
- Average cloud cover in September: 9
The month with the most cloud cover is March (Cloud cover 40).
The month with the least cloud cover is July (Cloud cover 6).
Average visibility in September
Yountville, 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).
Yountville, California, USA
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