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September Weather in Alton, United States

Last updated: June 24, 2025

In September, the average temperature in Alton, United States is a pleasant 18°C (64°F). Expect a minimum of 3°C (38°F) and a maximum of 33°C (91°F), giving you a taste of both cooler and warmer days. With an average precipitation of 66 mm (2.6 in) over 7 days, be prepared for some refreshing rain. Additionally, the average humidity sits at 71%, adding to the region's charm.

September Temperature in Alton

In September in Alton, the average temperature is 18°C (64°F). The maximum can reach 33°C (91°F), while the minimum can drop as low as 3°C (38°F). This makes it essential for travelers to pack a variety of clothing to adapt to the changing temperatures.

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 18°C (64°F), with highs reaching up to 33°C (91°F) and lows dropping to around 3°C (38°F).
JanFebMarAprMayJunJulAugSepOctNovDec242633445566727164523829
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 66 mm (2.6 in) over a period of 7 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 66 mm (2.6 inches) of precipitation spread over approximately 7 days.
JanFebMarAprMayJunJulAugSepOctNovDec75847712874871347466119110119
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 71%. With an average temperature of 18°C (64°F), this humidity feels like a warm embrace, making traveling a bit sticky but still pleasant as the warmth envelops you, urging you to explore the vibrant surroundings while staying hydrated.

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 71%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec86%84%82%80%72%72%67%66%71%79%84%81%
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 7, which corresponds to the high Exposure Category. This means that the time to burn is approximately 25 minutes. For more 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 7, which falls under the high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec3458910997532
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 Weather-5°C (24°F)75 mm (2.9 inches)86%moderate
February Weather-3°C (27°F)84 mm (3.3 inches)84%moderate
March Weather0°C (33°F)77 mm (3.0 inches)82%moderate
April Weather7°C (44°F)128 mm (5.0 inches)80%very high
May Weather13°C (56°F)74 mm (2.9 inches)72%very high
June Weather19°C (66°F)87 mm (3.4 inches)72%very high
July Weather22°C (72°F)134 mm (5.3 inches)67%very high
August Weather21°C (71°F)74 mm (2.9 inches)66%very high
September Weather18°C (64°F)66 mm (2.6 inches)71%high
October Weather11°C (52°F)119 mm (4.7 inches)78%moderate
November Weather3°C (39°F)110 mm (4.3 inches)84%moderate
December Weather-2°C (29°F)119 mm (4.7 inches)81%low

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