September Weather in Portola, United States

Last updated: June 24, 2025

In September, the average temperature in Portola, United States hovers around 15°C (60°F), with temperatures ranging from a brisk -2°C (28°F) to a warm 34°C (94°F). Expect a modest precipitation of 19 mm (0.7 in) spread across 3 days, alongside an average humidity level of 44%.

September Temperature in Portola

In September in Portola, the average temperature is 15°C (60°F). Maximum temperatures can reach 34°C (94°F), while minimums can drop as low as -2°C (28°F). Pack accordingly to enjoy a diverse range of weather conditions during your travels!

September Weather in Portola: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Portola, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Portola, September typically has an average temperature of 15°C (60°F), with highs reaching up to 34°C (94°F) and lows dropping to around -2°C (28°F).

Data source: Temperature data for Portola generated using information from the Copernicus Climate Change Service.

September Precipitation in Portola

In Portola in September, the precipitation amount is 19 mm (0.7 in) over a period of 3 days.

September Precipitation Trends in Portola

The chart displays monthly precipitation patterns in Portola, 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 Portola, September typically receives around 19 mm (0.7 inches) of precipitation spread over approximately 3 days.

Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.

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Millimeters (mm) Inches (in)

September Humidity in Portola

In Portola in September, humidity is 44%. With an average temperature of 15°C (60°F), this humidity feels like a refreshing breeze, making it pleasant for traveling and exploring the surroundings without feeling too hot or sticky.

September Average Humidity in Portola

This chart illustrates the average monthly humidity levels in Portola, 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 Portola is approximately 44%, offering insight into how humid the weather typically is during this month.

Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Portola

In Portola in September, the maximum UV index reaches 10, which corresponds to a very high Exposure Category. With a time to burn of just 15 minutes, it's crucial to take precautions. For more detailed information, you can check the Hourly UV Index in Portola.

Maximum UV Index Levels in Portola for September

The chart shows the monthly maximum UV Index (UVI) for Portola 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 Portola typically reaches 10, which falls under the very high exposure category.

Data source: Portola 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 Portola Compares to Other Months

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

This table compares monthly weather conditions in Portola, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
	Temperature	Precipitation	Humidity	UV
January Weather	-1°C (31°F)	170 mm (6.7 inches)	84%	moderate
February Weather	-1°C (30°F)	177 mm (7.0 inches)	84%	high
March Weather	1°C (34°F)	146 mm (5.7 inches)	83%	very high
April Weather	5°C (41°F)	72 mm (2.8 inches)	81%	very high
May Weather	10°C (51°F)	60 mm (2.3 inches)	74%	extreme
June Weather	16°C (62°F)	10 mm (0.4 inches)	64%	extreme
July Weather	21°C (70°F)	10 mm (0.4 inches)	44%	extreme
August Weather	20°C (68°F)	13 mm (0.5 inches)	36%	extreme
September Weather	15°C (60°F)	19 mm (0.7 inches)	44%	very high
October Weather	8°C (47°F)	43 mm (1.7 inches)	65%	high
November Weather	3°C (38°F)	79 mm (3.1 inches)	84%	moderate
December Weather	-2°C (29°F)	132 mm (5.2 inches)	83%	moderate