September weather forecastPortola, CA
September
Weather in September
September, the first month of the autumn in Portola, is also a moderately hot month, with an average temperature fluctuating between 73.8°F (23.2°C) and 42.3°F (5.7°C).Temperature
The move into September indicates a slight reduction in the average high-temperature, down from August's warm 81.1°F (27.3°C) to a still moderately hot 73.8°F (23.2°C). Contrasting the daytime warmth, Portola's September nights cool down to an average of 42.3°F (5.7°C).Humidity
In September, the average relative humidity is 46%.Rainfall
In Portola, in September, during 4.5 rainfall days, 0.43" (11mm) of precipitation is typically accumulated. Throughout the year, there are 80.1 rainfall days, and 22.95" (583mm) of precipitation is accumulated.Snowfall
January through June, September through December are months with snowfall in Portola. September is the first month it typically snows. Throughout September, in the average 0.4 snowfall days, it receives 1.02" (26mm) of snow. In Portola, California, during the entire year, snow falls for 69.3 days and aggregates up to 103.5" (2629mm) of snow.Daylight
In September, the average length of the day is 12h and 26min.On the first day of the month, sunrise is at 6:30 am and sunset at 7:32 pm. On the last day of September, sunrise is at 6:57 am and sunset at 6:45 pm PDT.
Sunshine
The average sunshine in September is 11h.UV index
In September, the average daily maximum UV index is 3. A UV Index estimate of 3 to 5 represents a medium health hazard from exposure to the Sun's UV rays for the ordinary person.Note: A maximum high UV index of 3 in September translates into the following recommendations:
Take precautions - Protection against skin and eye damage is obliged. The Sun's harshest UV rays are around midday; it's wise to seek shade and limit time outdoors. A wide-brimmed hat provides unparalleled sun protection for sensitive areas like the eyes, ears, and neck. Be prepared! The intensity of the Sun's UV radiation can be amplified nearly double due to snow reflection.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
Average temperature in September
Portola, CA
- Average high temperature in September: 73.8°F
The warmest month (with the highest average high temperature) is July (82.9°F).
The month with the lowest average high temperature is December (37.2°F).
- Average low temperature in September: 42.3°F
The month with the highest average low temperature is July (47.5°F).
The coldest month (with the lowest average low temperature) is December (21.6°F).
Average pressure in September
Portola, CA
- Average pressure in September: 29.93"Hg
The month with the highest atmospheric pressure is January (30.19"Hg).
The month with the lowest atmospheric pressure is June (29.9"Hg).
Average wind speed in September
Portola, CA
- Average wind speed in September: 5.2mph
The windiest month (with the highest average wind speed) is March (6.6mph).
The calmest months (with the lowest average wind speed) are August and September (5.2mph).
Average humidity in September
Portola, CA
- Average humidity in September: 46%
The months with the highest relative humidity are January and March (81%).
The months with the lowest relative humidity are July and August (40%).
Average rainfall in September
Portola, CA
- Average rainfall in September: 0.43"
The wettest month (with the highest rainfall) is March (4.02").
The driest month (with the least rainfall) is August (0.2").
Average rainfall days in September
Portola, CA
- Average rainfall days in September: 4.5 days
The month with the highest number of rainy days is May (11.8 days).
The month with the least rainy days is July (3.3 days).
Average snowfall in September
Portola, CA
- Average snowfall in September: 1.02"
The month with the highest snowfall is December (22.52").
The months with the least snowfall are July and August (0").
Average snowfall days in September
Portola, CA
- Average snowfall days in September: 0.4 days
The month with the highest number of snowfall days is March (14.7 days).
The months with the least snowfall days are July and August (0 days).
Average daylight in September /
Average sunshine in September
Portola, CA
- Average daylight in September: 12h and 24min
The month with the longest days is June (Average daylight: 14h and 54min).
The month with the shortest days is December (Average daylight: 9h and 24min).
- Average sunshine in September: 11h
The month with the most sunshine is July (Average sunshine: 12h).
The month with the least sunshine is January (Average sunshine: 5h).
Average sunshine days in September
Portola, CA
- Average sunshine days in September: 25 days
The month with the most sunshine days is August (26 days).
The month with the least sunshine days is March (11.8 days).
Average UV index in September
Portola, CA
- Average UV index in September: 3
The months with the highest UV index are June, July and August (UV index 5).
The month with the lowest UV index is November (UV index 1).
Average cloud cover in September
Portola, CA
- Average cloud cover in September: 12
The month with the most cloud cover is March (Cloud cover 47).
The month with the least cloud cover is July (Cloud cover 7).
Average visibility in September
Portola, CA
- Average visibility in September: 6mi
The months with the highest visibility are May, June, July, August, September, October and November (6mi).
The months with the lowest visibility are January and December (4mi).
