September Weather in Lake Forest, United States

Last updated: June 24, 2025

In Lake Forest, United States, the average temperature in September hovers around 22°C (72°F), with a minimum of 13°C (56°F) and a maximum reaching up to 40°C (104°F). Despite these warm conditions, you can expect only 3 mm (0.1 in) of precipitation over 0 days, complemented by an average humidity of 68%. Perfect weather for exploring or relaxing!

September Temperature in Lake Forest

In September in Lake Forest, the average temperature is 22°C (72°F). The maximum can reach 40°C (104°F), while the minimum can be as low as 13°C (56°F). It's advisable to pack both light clothing for the warm days and some layers for the cooler evenings.

September Weather in Lake Forest: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Lake Forest, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Lake Forest, September typically has an average temperature of 22°C (72°F), with highs reaching up to 40°C (104°F) and lows dropping to around 13°C (56°F).

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

September Precipitation in Lake Forest

In Lake Forest in September, the precipitation amount is 3 mm (0.1 in) during a total of 0 days.

September Precipitation Trends in Lake Forest

The chart displays monthly precipitation patterns in Lake Forest, 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 Lake Forest, September typically receives around 3 mm (0.1 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 Lake Forest

In Lake Forest in September humidity is 68%. With an average temperature of 22°C (72°F), this humidity feels like a warm embrace, slightly stifling but still manageable for traveling, creating an atmosphere that encourages leisurely outdoor activities while prompting occasional breaks for refreshment.

September Average Humidity in Lake Forest

This chart illustrates the average monthly humidity levels in Lake Forest, 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 Lake Forest is approximately 68%, 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 Lake Forest

In Lake Forest 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 Lake Forest.

Maximum UV Index Levels in Lake Forest for September

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

Data source: Lake Forest 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 Lake Forest Compares to Other Months

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

This table compares monthly weather conditions in Lake Forest, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
	Temperature	Precipitation	Humidity	UV
January Weather	13°C (56°F)	71 mm (2.8 inches)	74%	moderate
February Weather	13°C (56°F)	60 mm (2.3 inches)	79%	high
March Weather	14°C (58°F)	68 mm (2.7 inches)	75%	very high
April Weather	17°C (62°F)	27 mm (1.1 inches)	70%	very high
May Weather	17°C (64°F)	13 mm (0.5 inches)	70%	extreme
June Weather	20°C (68°F)	1 mm (0.0 inches)	72%	extreme
July Weather	23°C (73°F)	2 mm (0.1 inches)	73%	extreme
August Weather	23°C (74°F)	2 mm (0.1 inches)	69%	very high
September Weather	22°C (72°F)	3 mm (0.1 inches)	68%	very high
October Weather	20°C (69°F)	10 mm (0.4 inches)	67%	high
November Weather	17°C (62°F)	25 mm (1.0 inches)	68%	moderate
December Weather	13°C (56°F)	74 mm (2.9 inches)	71%	moderate