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September Weather in Mountain View, United States

Last updated: June 24, 2025

In September, the average temperature in Mountain View, United States hovers around 25°C (77°F), with a comfortable minimum of 20°C (68°F) and a pleasant maximum of 30°C (86°F). Prepare for some rain, as the region experiences approximately 93 mm (3.7 in) of precipitation over 22 days. Coupled with an average humidity of 82%, this climate creates a vibrant atmosphere perfect for exploring the beauty of Mountain View.

September Temperature in Mountain View

In September in Mountain View, the average temperature is 25°C (77°F). The maximum can reach 30°C (86°F), and the minimum can be as low as 20°C (68°F). This mild weather makes it an ideal time for outdoor activities and exploring the local attractions.

September Weather in Mountain View: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Mountain View, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Mountain View, September typically has an average temperature of 25°C (77°F), with highs reaching up to 30°C (86°F) and lows dropping to around 20°C (68°F).
JanFebMarAprMayJunJulAugSepOctNovDec717071727375767677757472
Data source: Temperature data for Mountain View generated using information from the Copernicus Climate Change Service.
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The average of daily temperatures (24 hours) calculated across all days in the month.

September Precipitation in Mountain View

In Mountain View in September, the precipitation amount is 93 mm (3.7 in) spread over 22 days.

September Precipitation Trends in Mountain View

The chart displays monthly precipitation patterns in Mountain View, with values for each month alongside September’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how September’s conditions compare to those of other months. In Mountain View, September typically receives around 93 mm (3.7 inches) of precipitation spread over approximately 22 days.
JanFebMarAprMayJunJulAugSepOctNovDec118209154117127909718893137108180
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Mountain View

In Mountain View in September, humidity is 82%. With an average temperature of 25°C (77°F), this humidity feels like a warm, oppressive blanket enveloping you as you explore, making every step feel more laborious and prompting the need for frequent hydration breaks.

September Average Humidity in Mountain View

This chart illustrates the average monthly humidity levels in Mountain View, with September’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In September, average humidity in Mountain View is approximately 82%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec79%79%77%80%80%82%83%84%82%83%83%81%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Mountain View

In Mountain View in September, the maximum UV index reaches 13, which corresponds to an extreme Exposure Category. With a time to burn of just 10 minutes, it's crucial to take protective measures. For detailed information, you can check the Hourly UV Index in Mountain View.

Maximum UV Index Levels in Mountain View for September

The chart shows the monthly maximum UV Index (UVI) for Mountain View in September, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues. In September, the maximum UV index in Mountain View typically reaches 13, which falls under the extreme exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec811121313131414131298
Data source: Mountain View September UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

  •  Extreme (11+): Avoid the sun, stay in shade.
  •  Very High (8-10): Limit sun exposure.
  •  High (6-7): Use SPF 30+ and protective clothing.
  •  Moderate (3-5): Midday shade recommended.
  •  Low (0-2): No protection needed.

How September Weather in Mountain View Compares to Other Months

Weather in Mountain View varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in Mountain View, focusing on differences in temperature, rainfall, humidity, and UV levels.

This table compares monthly weather conditions in Mountain View, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather22°C (71°F)118 mm (4.7 inches)79%very high
February Weather21°C (71°F)209 mm (8.2 inches)79%extreme
March Weather22°C (71°F)154 mm (6.0 inches)77%extreme
April Weather22°C (73°F)117 mm (4.6 inches)80%extreme
May Weather23°C (74°F)127 mm (5.0 inches)80%extreme
June Weather24°C (75°F)90 mm (3.5 inches)82%extreme
July Weather24°C (76°F)97 mm (3.8 inches)83%extreme
August Weather25°C (77°F)188 mm (7.4 inches)84%extreme
September Weather25°C (77°F)93 mm (3.7 inches)82%extreme
October Weather24°C (76°F)137 mm (5.4 inches)83%extreme
November Weather23°C (74°F)108 mm (4.2 inches)83%very high
December Weather22°C (72°F)180 mm (7.1 inches)81%very high

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