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May Weather in Boulder, United States

Last updated: June 24, 2025

In May, the average temperature in Boulder, United States hovers around 8°C (46°F). Expect temperatures to range from a brisk -8°C (17°F) at the lowest to a pleasant 25°C (77°F) at the highest. With 92 mm (3.6 in) of precipitation spread over 17 days, you might want to keep an umbrella handy. The average humidity sits at a comfortable 76%, adding to the season's unique charm.

May Temperature in Boulder

In May in Boulder, the average temperature is 8°C (46°F), with maximums reaching 25°C (77°F) and minimums dropping as low as -8°C (17°F). This wide temperature range makes it essential for travelers to pack layers to ensure comfort during their stay.

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

The chart illustrates May temperature patterns in Boulder, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Boulder, May typically has an average temperature of 8°C (46°F), with highs reaching up to 25°C (77°F) and lows dropping to around -8°C (17°F).
JanFebMarAprMayJunJulAugSepOctNovDec181528344657656354382718
Data source: Temperature data for Boulder 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.

May Precipitation in Boulder

In Boulder in May, the precipitation amount is 92 mm (3.6 in) spread over 17 days.

May Precipitation Trends in Boulder

The chart displays monthly precipitation patterns in Boulder, 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 Boulder, May typically receives around 92 mm (3.6 inches) of precipitation spread over approximately 17 days.
JanFebMarAprMayJunJulAugSepOctNovDec2356406892112443943443432
Data source: Precipitation data for May generated using information from the Copernicus Climate Change Service.
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May Humidity in Boulder

In Boulder in May, humidity is 76%. With an average temperature of 8°C (46°F), this humidity feels like a chilly dampness that seeps into your bones, making travel less enjoyable as the cold air mixes with the moisture, creating an uneasy, heavy atmosphere that can hinder your outdoor plans.

May Average Humidity in Boulder

This chart illustrates the average monthly humidity levels in Boulder, 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 Boulder is approximately 76%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec87%88%83%78%76%78%77%71%68%72%84%91%
Data source: Humidity data for May generated using information from the Copernicus Climate Change Service.

May UV Index in Boulder

In Boulder 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 Boulder.

Maximum UV Index Levels in Boulder for May

The chart shows the monthly maximum UV Index (UVI) for Boulder 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 Boulder typically reaches 9, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec34689111098532
Data source: Boulder 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 Boulder Compares to Other Months

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

This table compares monthly weather conditions in Boulder, showing how May’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather-8°C (18°F)23 mm (0.9 inches)87%moderate
February Weather-9°C (16°F)55 mm (2.2 inches)88%moderate
March Weather-2°C (28°F)40 mm (1.6 inches)83%high
April Weather1°C (34°F)68 mm (2.7 inches)78%very high
May Weather8°C (46°F)92 mm (3.6 inches)76%very high
June Weather14°C (57°F)112 mm (4.4 inches)78%extreme
July Weather18°C (65°F)44 mm (1.7 inches)77%very high
August Weather17°C (64°F)39 mm (1.5 inches)71%very high
September Weather12°C (54°F)43 mm (1.7 inches)68%very high
October Weather3°C (38°F)44 mm (1.7 inches)72%moderate
November Weather-3°C (28°F)34 mm (1.3 inches)84%moderate
December Weather-8°C (19°F)32 mm (1.3 inches)90%low

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