September Weather in Alton, United States

Last updated: June 24, 2025

In Alton, United States, the average temperature in September is a pleasant 19°C (66°F), with temperatures ranging from a cool 3°C (38°F) to a warm 33°C (92°F). Expect 101 mm (4.0 in) of precipitation spread over 8 days, and a comfortable average humidity of 75%.

September Temperature in Alton

In September in Alton, the average temperature is 19°C (66°F). Maximum temperatures can reach 33°C (92°F), while minimums can dip as low as 3°C (38°F). This variety in weather makes Alton an ideal destination for travelers seeking both warm and cool experiences.

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 19°C (66°F), with highs reaching up to 33°C (92°F) and lows dropping to around 3°C (38°F).

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

September Precipitation in Alton

In Alton in September, the precipitation amount is 101 mm (4.0 in) spread over 8 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 101 mm (4.0 inches) of precipitation spread over approximately 8 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 Alton

In Alton in September humidity is 75%. With an average temperature of 19°C (66°F), this humidity feels like a warm, enveloping blanket, making it slightly uncomfortable for traveling as you navigate through the thick, muggy air.

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 75%, 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 Alton

In Alton 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 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 8, which falls under the very high exposure category.

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.
	Temperature	Precipitation	Humidity	UV
January Weather	-6°C (21°F)	26 mm (1.0 inches)	80%	low
February Weather	-6°C (21°F)	32 mm (1.3 inches)	84%	moderate
March Weather	2°C (36°F)	72 mm (2.8 inches)	75%	moderate
April Weather	8°C (46°F)	95 mm (3.7 inches)	79%	very high
May Weather	15°C (60°F)	140 mm (5.5 inches)	74%	very high
June Weather	23°C (73°F)	114 mm (4.5 inches)	81%	extreme
July Weather	24°C (76°F)	72 mm (2.8 inches)	82%	very high
August Weather	22°C (72°F)	100 mm (3.9 inches)	80%	very high
September Weather	19°C (66°F)	101 mm (4.0 inches)	75%	very high
October Weather	9°C (49°F)	82 mm (3.2 inches)	77%	moderate
November Weather	2°C (36°F)	28 mm (1.1 inches)	85%	moderate
December Weather	-3°C (27°F)	39 mm (1.5 inches)	83%	moderate