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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 19°C (67°F), with a comfortable minimum of 10°C (51°F) and a pleasant maximum of 27°C (82°F). Expect around 85 mm (3.4 in) of precipitation spread over 10 days, contributing to an average humidity level of 79%. Embrace the blend of warmth and moisture that defines this month in Lake Forest!

September Temperature in Lake Forest

In September in Lake Forest, the average temperature is 19°C (67°F). Maximum temperatures can reach 27°C (82°F), while minimums can drop to as low as 10°C (51°F). This mild weather makes Lake Forest an ideal destination for travelers looking to enjoy comfortable temperatures.

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 19°C (67°F), with highs reaching up to 27°C (82°F) and lows dropping to around 10°C (51°F).
JanFebMarAprMayJunJulAugSepOctNovDec282835415062707267554034
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 precipitation amount is 85 mm (3.4 in) over the course of 10 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 85 mm (3.4 inches) of precipitation spread over approximately 10 days.
JanFebMarAprMayJunJulAugSepOctNovDec8585901251711056970851617775
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 79%. With an average temperature of 19°C (67°F), this humidity feels like a warm, enveloping blanket that makes traveling a bit more challenging, as the air is thick and can leave you feeling sluggish during outdoor adventures.

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 79%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec85%85%85%85%78%80%78%76%79%83%88%82%
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 is 8, which corresponds to a very high Exposure Category. This means that the time to burn is only 15 minutes. For more detailed information, you can refer to 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 8, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec24689101098532
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 Weather-2°C (28°F)85 mm (3.3 inches)85%low
February Weather-2°C (29°F)85 mm (3.3 inches)85%moderate
March Weather2°C (36°F)90 mm (3.6 inches)85%high
April Weather5°C (41°F)125 mm (4.9 inches)85%very high
May Weather10°C (50°F)171 mm (6.7 inches)78%very high
June Weather16°C (62°F)105 mm (4.1 inches)80%very high
July Weather21°C (71°F)69 mm (2.7 inches)78%very high
August Weather22°C (72°F)70 mm (2.8 inches)76%very high
September Weather19°C (67°F)85 mm (3.4 inches)79%very high
October Weather13°C (55°F)161 mm (6.3 inches)83%moderate
November Weather5°C (41°F)77 mm (3.0 inches)88%moderate
December Weather1°C (35°F)75 mm (2.9 inches)81%low

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