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September Weather in Lake Forest, United States

Last updated: June 24, 2025

In September, the average temperature in Lake Forest, United States hovers around 28°C (82°F), with a comfortable minimum of 24°C (75°F) and a peak of 33°C (92°F). However, be prepared for some rain, as precipitation amounts can reach 215 mm (8.5 in) over 24 days. With an average humidity of 76%, you'll feel the warmth in the air, making it a perfect time to enjoy the vibrant atmosphere.

September Temperature in Lake Forest

In September in Lake Forest, the average temperature is 28°C (82°F), with a maximum reaching 33°C (92°F) and a minimum dipping to 24°C (75°F). This pleasant climate makes it an ideal time for travelers to enjoy outdoor activities and explore the local attractions.

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 28°C (82°F), with highs reaching up to 33°C (92°F) and lows dropping to around 24°C (75°F).
JanFebMarAprMayJunJulAugSepOctNovDec697373777981838382807572
Data source: Temperature data for Lake Forest 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 Lake Forest

In Lake Forest in September, the total precipitation amount is 215 mm (8.5 in) spread out over 24 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 215 mm (8.5 inches) of precipitation spread over approximately 24 days.
JanFebMarAprMayJunJulAugSepOctNovDec355330751701911881922151679445
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Lake Forest

In Lake Forest in September humidity is 76%. With an average temperature of 28°C (82°F), this humidity feels like a warm blanket enveloping you, making travel feel sticky and sluggish as you navigate through the heat, leaving you constantly seeking shade and refreshing beverages.

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 76%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec81%80%76%73%71%70%70%72%76%79%80%81%
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 11, which corresponds to an extreme Exposure Category. With a time to burn of just 10 minutes, it's essential to take precautions. For more details, 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 11, which falls under the extreme exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec69101212131212111086
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.
 TemperaturePrecipitationHumidityUV
January Weather21°C (69°F)35 mm (1.4 inches)81%high
February Weather23°C (73°F)53 mm (2.1 inches)79%very high
March Weather23°C (73°F)30 mm (1.2 inches)76%very high
April Weather25°C (77°F)75 mm (2.9 inches)73%extreme
May Weather26°C (79°F)170 mm (6.7 inches)71%extreme
June Weather27°C (82°F)191 mm (7.5 inches)69%extreme
July Weather28°C (83°F)188 mm (7.4 inches)70%extreme
August Weather28°C (83°F)192 mm (7.6 inches)72%extreme
September Weather28°C (82°F)215 mm (8.5 inches)76%extreme
October Weather27°C (80°F)167 mm (6.6 inches)79%very high
November Weather24°C (75°F)94 mm (3.7 inches)80%very high
December Weather22°C (72°F)45 mm (1.8 inches)81%high

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