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September Weather in Alton, United States

Last updated: June 24, 2025

In September, the average temperature in Alton, United States hovers around 23°C (73°F). Expect a range from a cool 7°C (46°F) to a warm 35°C (96°F). With precipitation measuring 62 mm (2.4 in) over approximately 6 days, the air often feels pleasantly damp, complemented by an average humidity of 68%.

September Temperature in Alton

In September in Alton, the average temperature is a pleasant 23°C (73°F). Maximum temperatures can reach up to 35°C (96°F), while minimum temperatures can drop as low as 7°C (46°F). This variation makes it essential for travelers to pack versatile clothing to enjoy both warm days and cooler evenings.

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

The chart illustrates September temperature patterns in Alton, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Alton, September typically has an average temperature of 23°C (73°F), with highs reaching up to 35°C (96°F) and lows dropping to around 7°C (46°F).
JanFebMarAprMayJunJulAugSepOctNovDec363950566775807773604642
Data source: Temperature data for Alton 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 Alton

In Alton in September, the precipitation amount is 62 mm (2.4 in), spread over the course of 6 days.

September Precipitation Trends in Alton

The chart displays monthly precipitation patterns in Alton, 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 Alton, September typically receives around 62 mm (2.4 inches) of precipitation spread over approximately 6 days.
JanFebMarAprMayJunJulAugSepOctNovDec851111481641818580107621217781
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Alton

In Alton in September humidity is 68%. With an average temperature of 23°C (73°F), this humidity feels like a soft blanket wrapping around you, making every step outside feel a bit heavier, but offering a warm embrace that encourages leisurely exploration and a relaxed pace for travel.

September Average Humidity in Alton

This chart illustrates the average monthly humidity levels in Alton, 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 Alton is approximately 68%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec83%81%80%80%83%83%76%69%68%72%83%87%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Alton

In Alton 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 Alton.

Maximum UV Index Levels in Alton for September

The chart shows the monthly maximum UV Index (UVI) for Alton 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 Alton typically reaches 9, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec36710111111109753
Data source: Alton 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 Alton Compares to Other Months

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

This table compares monthly weather conditions in Alton, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather2°C (36°F)85 mm (3.3 inches)83%moderate
February Weather4°C (40°F)111 mm (4.4 inches)81%high
March Weather10°C (50°F)148 mm (5.8 inches)80%high
April Weather13°C (56°F)164 mm (6.5 inches)80%very high
May Weather19°C (67°F)181 mm (7.1 inches)83%extreme
June Weather24°C (76°F)85 mm (3.3 inches)83%extreme
July Weather26°C (80°F)80 mm (3.2 inches)76%extreme
August Weather25°C (77°F)106 mm (4.2 inches)69%very high
September Weather23°C (73°F)62 mm (2.4 inches)68%very high
October Weather16°C (60°F)121 mm (4.8 inches)72%high
November Weather8°C (47°F)77 mm (3.0 inches)83%moderate
December Weather6°C (42°F)81 mm (3.2 inches)86%moderate

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