May Weather in Alton, United States

Last updated: June 24, 2025

In Alton, United States, the average temperature in May hovers around 15°C (60°F), making it a pleasant time of year. Be prepared for a temperature range that can dip to 0°C (33°F) and soar to 35°C (95°F). Expect around 140 mm (5.5 in) of precipitation spread over 15 days, and enjoy the humidity, which averages a comfortable 74%.

May Temperature in Alton

In May in Alton, the average temperature is 15°C (60°F). Maximums can reach 35°C (95°F), and minimums can be as low as 0°C (33°F). Be sure to pack accordingly for a range of temperatures to fully enjoy your trip.

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

The chart illustrates May 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, May typically has an average temperature of 15°C (60°F), with highs reaching up to 35°C (95°F) and lows dropping to around 0°C (33°F).

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

May Precipitation in Alton

In Alton in May, the total precipitation amount is 140 mm (5.5 in) over a span of 15 days.

May Precipitation Trends in Alton

The chart displays monthly precipitation patterns in Alton, with values for each month alongside May’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how May’s conditions compare to those of other months. In Alton, May typically receives around 140 mm (5.5 inches) of precipitation spread over approximately 15 days.

Data source: Precipitation data for May generated using information from the Copernicus Climate Change Service.

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Millimeters (mm) Inches (in)

May Humidity in Alton

In Alton in May humidity is 74%. With an average temperature of 15°C (60°F), this humidity feels like a warm embrace that can make outdoor activities feel slightly stifling, so travelers should be prepared to hydrate frequently and take breaks in the shade.

May Average Humidity in Alton

This chart illustrates the average monthly humidity levels in Alton, with May’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In May, average humidity in Alton is approximately 74%, offering insight into how humid the weather typically is during this month.

Data source: Humidity data for May generated using information from the Copernicus Climate Change Service.

May UV Index in Alton

In Alton in May, 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 May

The chart shows the monthly maximum UV Index (UVI) for Alton in May, 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 May, the maximum UV index in Alton typically reaches 9, which falls under the very high exposure category.

Data source: Alton May 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 May 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 May’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 May’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