May Weather in Boulder, United States

Last updated: February 24, 2025

May in Boulder, United States, presents a dynamic interplay of weather patterns, showcasing maximum temperatures reaching up to 27°C (81°F), while average daily temperatures settle comfortably around 10°C (50°F). Nighttime can be brisk, with minimum temperatures dipping to -9°C (17°F). This month experiences considerable precipitation, accumulating 134 mm (5.3 in) over about 16 days, contributing to a humidity level of 66%. As spring unfolds, residents and visitors alike can anticipate vibrant greens and blooming flora, tempered by occasional showers that nurture the landscape.

May Temperature in Boulder

As spring blossoms into full swing, May in Boulder, United States brings a refreshing transition with temperatures steadily warming up. The month sees a noticeable increase in warmth, with minimum temperatures averaging a chilly -9°C (17°F), while daytime highs can reach a pleasant 27°C (81°F). As the average temperature hovers around 10°C (50°F), the shift from the frigid winter months becomes increasingly evident. This newfound warmth encourages outdoor activities and showcases the vibrant beauty of the season. By contrasting the preceding months, it's clear that May serves as a vital bridge, welcoming residents and visitors alike to embrace the joys of spring before the heat of summer sets in.

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.
JanFebMarAprMayJunJulAugSepOctNovDec262535425063686661443629
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

May marks a remarkable peak in precipitation for Boulder, United States, as it receives a substantial 134 mm (5.3 in) of rain over 16 days—the highest monthly total for the year. This significant increase from previous months highlights May's role as a transitional period, ensuring lush greenery flourishes as warmer days approach. In contrast to the early months, where precipitation steadily rises from 25 mm (1.0 in) in January to 68 mm (2.7 in) in April, May's rainfall is a dramatic leap. Following this wet month, June sees a notable decrease to 74 mm (2.9 in), suggesting that while May nurtures the landscape, summer's drier patterns begin to take hold. This seasonality in Boulder’s precipitation not only shapes its natural beauty but also influences local activities and outdoor plans.

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.
JanFebMarAprMayJunJulAugSepOctNovDec2536636813474716842483020
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, United States, the humidity levels exhibit a noteworthy decline as spring transitions into summer. Starting with a high 88% in January, the humidity steadily decreases each month, reaching 66% by May. This marks a significant drop compared to April’s 76%, indicating the beginning of drier conditions as warmer weather approaches. Following May, humidity continues its downward trend, bottoming out at 52% in July, before gradually rising again in the fall. This seasonal pattern not only highlights Boulder’s shift from a moist winter climate to a comfortably drier summer but also sets the stage for a vibrant outdoor lifestyle as residents enjoy the increasingly pleasant weather.

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, allowing you to see how May's humidity levels compare to other months.
JanFebMarAprMayJunJulAugSepOctNovDec88%87%81%76%67%58%52%56%65%76%82%89%
Data source: Humidity data for May generated using information from the Copernicus Climate Change Service.

May UV Index in Boulder

As May rolls into Boulder, the UV Index remains at a striking 11, categorizing it as extreme and signaling that outdoor enthusiasts should prioritize sun protection. This level of UV radiation is consistent with the intensity observed in April, indicating that springtime sunlight still poses a significant risk, matching the greening landscape. Interestingly, this trend of high UV readings will extend into June and July, which both feature a UV Index of 12, suggesting a prolonged season of intense sun exposure. With a burn time of just 10 minutes, those venturing outside should plan accordingly to avoid sunburn. As you enjoy the vibrant outdoors, be sure to stay informed about local UV conditions by checking Boulder UV Index.

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.
JanFebMarAprMayJunJulAugSepOctNovDec469111112121110754
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.

May Sunshine in Boulder

In Boulder, Colorado, May shines particularly bright, boasting 330 hours of dazzling sunshine—an increase from the previous months and setting the stage for summer. As the days grow longer and warmer, it’s clear that May is the gateway to a vibrant season, following April’s promising 304 hours. This upward trend in sunlight continues into June and July, peaking at 374 hours and 378 hours, respectively. With each passing month, Boulder basks in more sunlight, inviting residents and visitors alike to enjoy the great outdoors. This blossoming energy culminates in July, before gradually tapering off as summer transitions to fall, leaving behind the warm embrace of sunny days.

Monthly Sunshine Duration in Boulder: May Highlighted

The May sunshine duration represents the total number of hours Boulder experiences direct sunlight during the month of May, excluding cloudy or obstructed periods. This chart compares the sunshine duration of May with the other months of the year.
JanFebMarAprMayJunJulAugSepOctNovDec185h237h288h304h330h374h378h351h309h274h249h238h
Data source: Boulder May Sunshine duration data generated using information from the Copernicus Climate Change Service.

Chance of Sun in Boulder During May

As spring transitions to summer, the likelihood of sunny weather in Boulder significantly dips in May, with a chance of sun at 41%. This marks a noticeable decline from the earlier spring months, where January through April see consistently higher probabilities of clear skies. While the chase for sunshine might feel elusive in May, the trend shifts dramatically as the year progresses; the chances increase to 55% in June and peak at 69% in September. This pattern suggests that while May may present a cloudier forecast, the sun is eager to make a comeback in the following months, inviting residents and visitors alike to embrace the warmth of summer.

Percentage of Sunny Days in May in Boulder

The chart illustrates the percentage of sunny days in Boulder throughout the year, with May highlighted. It highlights the variation in sunshine across each month and provides an overview of the typical frequency of sunny days, offering insights into how often Boulder experiences clear skies throughout the year.
JanFebMarAprMayJunJulAugSepOctNovDec56%52%50%51%41%55%59%65%69%63%63%68%
Data source: Boulder May chance of sun data, generated using information from the Copernicus Climate Change Service.

Daylight Hours in Boulder in May

As spring transitions into summer, May in Boulder ushers in a delightful increase in daylight, boasting 14 hours of sun. This month stands out as a pivotal point in the yearly cycle, reflecting the gradual but noticeable lengthening of days that began in January with just 9 hours of daylight. As the seasons progress, daylight steadily accumulates, reaching a peak during the summer months before tapering off again in a gentle decline toward winter. The smooth rise from 11 hours in March and 13 hours in April showcases the compelling hand of nature, reminding us of the vibrant life that flourishes under the sun's warm embrace. With the sun illuminating Boulder for longer periods, May is a perfect time to enjoy outdoor activities and revel in the beauty of the longer days.

Average Daylight Hours in Boulder for May

The chart illustrates the variation in daylight duration in Boulder throughout the year, with May highlighted. It shows the monthly changes in daylight hours, calculated by summing the hours between sunrise and sunset.
JanFebMarAprMayJunJulAugSepOctNovDec9h 40m10h 41m11h 58m13h 18m14h 24m14h 57m14h 39m13h 39m12h 23m11h 5m9h 56m9h 21m
Data source: Boulder daylight hours, calculated by summing the hours between sunrise and sunset for each day.

May Winds in Boulder

In Boulder, United States, the month of May brings a gentle breeze with an average wind speed of 2.1 m/s (5 mph), marking a continuing trend of softening winds as spring progresses. Following a peak in November and December—when gusts are notably stronger, averaging around 2.9 to 3.0 m/s (6-7 mph)—winds gradually decrease as winter gives way to warmer months. This decline becomes more apparent in May, where wind speeds dip slightly from April's 2.4 m/s. As summer approaches, the environment embraces a serene calm, with consistent yet mild breezes that harmonize beautifully with the vibrancy of nature during this time of year.

Average May Wind Speed in Boulder

The chart displays monthly wind speed patterns in Boulder, with values for each month shown alongside May's data, which is highlighted for easy comparison. It illustrates the average wind speed, offering insights into how May's wind conditions compare to the rest of the year.
JanFebMarAprMayJunJulAugSepOctNovDec2.62.82.52.42.1 m/s2.32.12.22.22.42.93.0
Data source: Boulder May wind data, generated using information from the Copernicus Climate Change Service.

How May Weather in Boulder Compares to Other Months

The weather in Boulder changes throughout the year, offering a unique experience in each season. Below is a month-by-month comparison of May's weather with other months, highlighting differences in temperature, precipitation, and other key factors. Click on each section to discover seasonal trends in Boulder and find detailed weather information for every month.

The weather in May contrasts significantly with that of January, showcasing the shift from the depths of winter to the onset of spring. In May, temperatures range from a chilly minimum of -9°C (17°F) to a pleasant average of 10°C (50°F), peaking at a warm 27°C (81°F). This month sees a notable increase in precipitation, totaling 134 mm (5.3 in) over 16 days, while humidity averages around 66%. In stark contrast, January experiences much colder temperatures, with a minimum of -24°C (-12°F) and an average of -3°C (26°F), reaching a maximum of just 15°C (59°F). Precipitation is minimal during January, amounting to only 25 mm (1.0 in) across 5 days, accompanied by a higher humidity of 88%. For more details on January weather, you can check Boulder weather in January.

May and February present strikingly different weather patterns. In May, temperatures range from a chilly minimum of -9°C (17°F) to a pleasant maximum of 27°C (81°F), averaging around 10°C (50°F). This month also sees considerable precipitation with 134 mm (5.3 in) falling over 16 days, accompanied by a humidity level of 66%. In contrast, February is significantly colder, with temperatures plummeting to a minimum of -26°C (-14°F) and peaking at a maximum of 20°C (69°F), averaging -4°C (26°F). Precipitation is lighter in February at 36 mm (1.4 in) over 9 days, but the humidity is higher at 87%. For more insights, check out Boulder weather in February.

When comparing the weather of May and March, it's clear that May offers a milder and more varied climate. In May, temperatures range from a chilly minimum of -9°C (17°F) to a warm maximum of 27°C (81°F), averaging around 10°C (50°F). The month experiences a moderate level of precipitation at 134 mm (5.3 in) over 16 days, with a humidity level of 66%. In contrast, March is significantly colder, with temperatures ranging from a low of -21°C (-5°F) to a high of 23°C (73°F), yielding an average temperature of just 2°C (35°F). March also sees less precipitation at 62 mm (2.5 in) but has higher humidity at 81%. For more detailed information about the weather in March, you can check this link: Boulder weather in March.

In comparing the weather of April and May, May generally sees much milder temperatures, with a minimum of -9°C (17°F) and an average of 10°C (50°F), compared to April's colder minimum of -17°C (2°F) and an average of only 5°C (42°F). May also experiences a wider range of temperatures, peaking at a warm 27°C (81°F), whereas April's maximum reaches 24°C (75°F). While both months see precipitation, May is significantly wetter, with 134 mm (5.3 in) over 16 days compared to April's 68 mm (2.7 in) over 12 days. It's worth noting that April has slightly higher humidity levels, averaging 76%, compared to May's 66%. For more insights on April weather, you can check Boulder weather in April.

In May, temperatures ranged from a chilly minimum of -9°C (17°F) to a pleasant maximum of 27°C (81°F), with an average of 10°C (50°F). The month saw considerable precipitation, totaling 134 mm (5.3 in) over 16 days, contributing to a relatively high humidity level of 66%. In contrast, June experiences a milder climate with minimum temperatures starting at 3°C (37°F) and soaring to a maximum of 34°C (93°F), resulting in a warmer average of 17°C (63°F). Additionally, June has less precipitation at 74 mm (2.9 in) over 14 days, and the humidity drops to a more comfortable 58%. For more details, check out Boulder weather in June.

In May, temperatures can be quite variable, ranging from a chilly minimum of -9°C (17°F) to a warm maximum of 27°C (81°F), with an average of 10°C (50°F). The month is also characterized by significant precipitation, totaling 134 mm (5.3 in) over 16 days, contributing to a higher humidity level of 66%. In contrast, July enjoys much warmer conditions, with minimum temperatures of 7°C (45°F) and maximums peaking at 34°C (93°F), averaging around 20°C (68°F). Precipitation drops to 71 mm (2.8 in) over 16 days, and humidity is lower at 52%. For more details, check out Boulder weather in July.

May and August present quite a contrast in weather patterns. In May, temperatures range from a chilly minimum of -9°C (17°F) to a pleasant average of 10°C (50°F), peaking at a warm 27°C (81°F). The month also sees considerable precipitation, totaling 134 mm (5.3 in) over 16 days, contributing to a relatively high humidity level of 66%. In contrast, August enjoys a warmer climate, with a minimum of 7°C (45°F), an average of 19°C (67°F), and a maximum temperature soaring to 33°C (91°F). Additionally, August experiences significantly less rainfall, with only 67 mm (2.7 in) over 13 days and lower humidity at 56%. For more detailed information, you can visit Boulder weather in August.

May and September present distinct weather characteristics, reflecting the transition from spring to fall. In May, temperatures can range dramatically, with a minimum of -9°C (17°F) and a maximum of 27°C (81°F), while averaging around 10°C (50°F). This month experiences considerable precipitation, totaling 134 mm (5.3 in) over 16 days, leading to a relatively humid atmosphere at 66%. In contrast, September offers a warmer climate, with average temperatures peaking at 16°C (61°F) and reaching a maximum of 33°C (92°F), while only dipping to -4°C (25°F) at night. Additionally, rainfall is significantly lower in September, totaling 42 mm (1.6 in) over just 8 days, with humidity slightly decreasing to 65%. For more details on September weather, visit Boulder weather in September.

May and October present distinct climatic contrasts, with May typically experiencing milder temperatures and more precipitation. In May, temperatures range from a minimum of -9°C (17°F) to a maximum of 27°C (81°F), averaging around 10°C (50°F), along with 134 mm (5.3 in) of precipitation spread over 16 days and a humidity level of 66%. Conversely, October sees a lower temperature range, with minimums dipping to -20°C (-5°F) and maximums reaching 26°C (79°F), averaging 7°C (45°F). The month also offers much less rainfall, totaling only 48 mm (1.9 in) over 7 days and accompanying higher humidity at 76%. Thus, while May is characterized by a more varied weather pattern, October brings cooler temperatures and drier conditions. For more detailed insights, you can check Boulder weather in October.

May and November present quite contrasting weather patterns. In May, temperatures range from a chilly -9°C (17°F) at night to a warm 27°C (81°F) during the day, with an average of 10°C (50°F). The month sees significant precipitation, totaling 134 mm (5.3 in) over about 16 days, while the humidity hovers around 66%. In stark contrast, November experiences much colder temperatures, with nighttime lows reaching -16°C (3°F) and daytime highs peaking at 22°C (71°F), resulting in an average of just 2°C (36°F). Additionally, November is much drier, with only 30 mm (1.2 in) of precipitation across 6 days, but it is more humid, with humidity levels rising to 82%. For a more detailed look at November weather, you can check Boulder weather in November.

May and December present stark contrasts in weather patterns. In May, temperatures range from a chilly -9°C (17°F) at their lowest to a warm 27°C (81°F) at their peak, with an average of 10°C (50°F). The month experiences significant precipitation of 134 mm (5.3 in) over 16 days, coupled with a moderate humidity level of 66%. In contrast, December is much colder, with temperatures dipping as low as -19°C (-1°F) and averaging around -2°C (29°F), while peaking at 19°C (67°F). This month brings only 19 mm (0.8 in) of precipitation spread over just 4 days, and higher humidity at 89%. For more detailed insights, check out Boulder weather in December.

Compare Boulder's Climate with Cities Worldwide

Conclusion: What to Expect From May Weather in Boulder

As May rolls into Boulder, the weather starts to showcase a vibrant transformation, departing from the chill of earlier months. With temperatures reaching up to a pleasant 27°C (81°F), residents and visitors alike can finally bask in the warmth of spring. However, this month also brings about the potential for unpredictable rain, with precipitation occurring on 16 days and a total of 134 mm (5.3 in) accumulated, a stark contrast to the drier spells of the preceding months. The average temperature settles around 10°C (50°F), highlighting the cool evenings that remind us that summer is just around the corner. With a humidity level hovering around 66%, the air feels fresh but can also be a touch damp, adding to the landscape’s lush charm. For those curious about the broader climate trends, delve deeper into the seasonal patterns at Boulder Climate to truly appreciate what makes May in Boulder uniquely delightful.