September Weather in Vacaville, United States

Last updated: June 24, 2025

In Vacaville, United States, the average temperature in September hovers around 21°C (71°F), with a comfortable humidity level of 44%. Temperatures can fluctuate significantly, ranging from a cool minimum of 8°C (46°F) to a scorching maximum of 43°C (110°F). Thankfully, you can expect minimal rainfall, with only 1 mm (0.0 in) of precipitation falling over the course of 0 days.

September Temperature in Vacaville

In September in Vacaville, the average temperature is 21°C (71°F). Maximums can reach 43°C (110°F), while minimums can drop as low as 8°C (46°F). Travelers should be prepared for a wide range of temperatures and plan accordingly for both warm and cooler conditions.

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

The chart illustrates September temperature patterns in Vacaville, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Vacaville, September typically has an average temperature of 21°C (71°F), with highs reaching up to 43°C (110°F) and lows dropping to around 8°C (46°F).

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

September Precipitation in Vacaville

In Vacaville in September, the precipitation amount is 1 mm (0.0 in) during a span of 0 days.

September Precipitation Trends in Vacaville

The chart displays monthly precipitation patterns in Vacaville, 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 Vacaville, September typically receives around 1 mm (0.0 inches) of precipitation spread over approximately 0 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 Vacaville

In Vacaville in September humidity is 44%. With an average temperature of 21°C (71°F), this humidity feels like a comfortable and refreshing climate for traveling, allowing for enjoyable outdoor activities and leisurely explorations without feeling too sticky or oppressive.

September Average Humidity in Vacaville

This chart illustrates the average monthly humidity levels in Vacaville, 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 Vacaville 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 Vacaville

In Vacaville in September, the maximum UV index is 9, which corresponds to a very high Exposure Category. The time to burn is just 15 minutes, so it's essential to take precautions. For detailed information, you can check the Hourly UV Index in Vacaville.

Maximum UV Index Levels in Vacaville for September

The chart shows the monthly maximum UV Index (UVI) for Vacaville 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 Vacaville typically reaches 9, which falls under the very high exposure category.

Data source: Vacaville 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 Vacaville Compares to Other Months

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

This table compares monthly weather conditions in Vacaville, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
	Temperature	Precipitation	Humidity	UV
January Weather	10°C (50°F)	119 mm (4.7 inches)	84%	moderate
February Weather	12°C (53°F)	102 mm (4.0 inches)	84%	moderate
March Weather	13°C (56°F)	77 mm (3.0 inches)	83%	high
April Weather	16°C (61°F)	32 mm (1.3 inches)	81%	very high
May Weather	19°C (66°F)	17 mm (0.7 inches)	74%	very high
June Weather	22°C (71°F)	1 mm (0.1 inches)	64%	extreme
July Weather	22°C (71°F)	0 mm (0.0 inches)	44%	extreme
August Weather	22°C (72°F)	0 mm (0.0 inches)	36%	very high
September Weather	21°C (71°F)	1 mm (0.0 inches)	44%	very high
October Weather	18°C (65°F)	26 mm (1.0 inches)	65%	high
November Weather	13°C (56°F)	38 mm (1.5 inches)	84%	moderate
December Weather	10°C (50°F)	85 mm (3.3 inches)	83%	moderate