May weather forecast
Boulder, CO

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The old building of the University of Colorado in Boulder, Colorado
The old building of the University of Colorado in Boulder, Colorado

Weather in May

May denotes the onset of more agreeable conditions in Boulder, as spring starts to give way to the impending summer. Overall, it is characterised by the longest daylight span of the year, warmer temperatures and heightened humidity levels. By this time, rain peaks to its yearly high, reaching an amount of about 2.48" (63mm). The advent of June will denote increased temperatures and the official beginning of the summer season. As such, May is a month of pleasant and diverse climatic shifts.

Temperature

The coming of May brings a minor shift in Boulder's weather, with average high-temperatures adjusting from April's fresh 52.3°F (11.3°C) to an enjoyable 61°F (16.1°C). May in Boulder is characterized by a distinct thermal shift, with nighttime lows averaging at an icy 38.7°F (3.7°C).

Humidity

The average relative humidity in May in Boulder is 58%.

Rainfall

The month with the most rainfall is May, when the rain falls for 17.5 days and typically aggregates up to 2.48" (63mm) of precipitation.

Snowfall

January through May, October through December are months with snowfall in Boulder. May is the last month it regularly snows in Boulder. During 1.7 snowfall days, in May, Boulder aggregates 1.65" (42mm) of snow. Throughout the year, in Boulder, there are 44.8 snowfall days, and 37.01" (940mm) of snow is accumulated.

Daylight

In May, the average length of the day is 14h and 25min.
On the first day of May in Boulder, sunrise is at 5:59 am and sunset at 7:56 pm. On the last day of the month, sunrise is at 5:34 am and sunset at 8:23 pm MDT.

Sunshine

The average sunshine in May is 10.7h.

UV index

In May, the average daily maximum UV index is 4. A UV Index estimate of 3 to 5 represents a medium health hazard from unprotected exposure to Sun's UV rays for the average person.
Note: A daily maximum UV index of 4 in May translates into the following instructions:
Take precautions. Light skin individuals may get burned in less than 30 minutes. Avoiding direct sun during mid-day hours can prevent harmful UV radiation exposure. To cut down UV radiation exposure by about half, sport a wide-brim hat. Keep in mind! Snow's reflective quality can nearly double the intensity of the Sun's UV radiation.
Updated: Feb 10, 2024
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate

Frequently asked questions

What is the average May temperature in Boulder?

An average high-temperature, in May, in Boulder, is 61°F (16.1°C) and the average low-temperature is 38.7°F (3.7°C).

What is the average humidity in May in Boulder?

The average relative humidity in May in Boulder is 58%.

What is the rainiest month in Boulder?

The month with the most rainfall in Boulder, Colorado, is May, when the rain falls for 17.5 days and typically aggregates up to 2.48" (63mm) of precipitation.

How much does it rain in Boulder in May?

In Boulder, during May, the rain falls for 17.5 days and regularly aggregates up to 2.48" (63mm) of precipitation.

What is the last month it snows in Boulder?

May is the last month it regularly snows in Boulder. During 1.7 snowfall days, in May, Boulder aggregates 1.65" (42mm) of snow.

How many hours of daylight does Boulder have in May?

In Boulder, the average day length in May is 14h and 25min.

When are sunrise and sunset in May in Boulder?

On the first day of May, sunrise is at 5:59 am and sunset at 7:56 pm. On the last day of the month, sunrise is at 5:34 am and sunset at 8:23 pm MDT.

How many hours of sunshine does Boulder have in May?

In Boulder, Colorado, the average sunshine duration in May is 10.7h.

What is the UV index reading in May in Boulder?

The average daily maximum UV index in May in Boulder, Colorado, is 4. A UV Index value of 3 to 5 symbolizes a medium hazard to health from exposure to Sun's UV rays.
Average humidity
Average rainfall days
Average snowfall days
Average daylight
Average sunshine
Average sunshine days
Average UV index
Average cloud cover
Average visibility

Average temperature in May
Boulder, CO

Average temperature in May - Boulder, CO
  • Average high temperature in May: 61°F

The warmest month (with the highest average high temperature) is July (80.4°F).
The month with the lowest average high temperature is December (35.2°F).

  • Average low temperature in May: 38.7°F

The month with the highest average low temperature is July (55.2°F).
The coldest month (with the lowest average low temperature) is February (18°F).

Average pressure in May
Boulder, CO

Average pressure in May - Boulder, CO
  • Average pressure in May: 29.92"Hg

The month with the highest atmospheric pressure is January (30.15"Hg).
The months with the lowest atmospheric pressure are April, May and June (29.92"Hg).

Average wind speed in May
Boulder, CO

Average wind speed in May - Boulder, CO
  • Average wind speed in May: 5.7mph

The windiest month (with the highest average wind speed) is January (7.3mph).
The calmest months (with the lowest average wind speed) are May, July, August and September (5.7mph).

Average humidity in May
Boulder, CO

Average humidity in May - Boulder, CO
  • Average humidity in May: 58%

The month with the highest relative humidity is February (70%).
The months with the lowest relative humidity are June, August and September (45%).

Average rainfall in May
Boulder, CO

Average rainfall in May - Boulder, CO
  • Average rainfall in May: 2.48"

The wettest month (with the highest rainfall) is May (2.48").
The driest month (with the least rainfall) is January (0.39").

Average rainfall days in May
Boulder, CO

Average rainfall days in May - Boulder, CO
  • Average rainfall days in May: 17.5 days

The month with the highest number of rainy days is July (17.8 days).
The month with the least rainy days is November (3.3 days).

Average snowfall in May
Boulder, CO

Average snowfall in May - Boulder, CO
  • Average snowfall in May: 1.65"

The month with the highest snowfall is April (7.76").
The months with the least snowfall are June, July, August and September (0").

Average snowfall days in May
Boulder, CO

Average snowfall days in May - Boulder, CO
  • Average snowfall days in May: 1.7 days

The month with the highest number of snowfall days is February (10.3 days).
The months with the least snowfall days are June, July and August (0 days).

Average daylight in May /
Average sunshine in May
Boulder, CO

Average daylight in May / Average sunshine in May - Boulder, CO
  • Average daylight in May: 14h and 2min

The month with the longest days is June (Average daylight: 15h and 0min).
The month with the shortest days is December (Average daylight: 9h and 24min).

  • Average sunshine in May: 10h and 4min

The months with the most sunshine are June and July (Average sunshine: 11h and 42min).
The month with the least sunshine is February (Average sunshine: 6h and 36min).

Average sunshine days in May
Boulder, CO

Average sunshine days in May - Boulder, CO
  • Average sunshine days in May: 10.9 days

The month with the most sunshine days is January (22.2 days).
The month with the least sunshine days is July (9.9 days).

Average UV index in May
Boulder, CO

Average UV index in May - Boulder, CO
  • Average UV index in May: 4

The months with the highest UV index are June, July and August (UV index 5).
The months with the lowest UV index are January, February, November and December (UV index 2).

Average cloud cover in May
Boulder, CO

Average cloud cover in May - Boulder, CO
  • Average cloud cover in May: 28

The months with the most cloud cover are April and May (Cloud cover 28).
The month with the least cloud cover is September (Cloud cover 16).

Average visibility in May
Boulder, CO

Average visibility in May - Boulder, CO
  • Average visibility in May: 6mi

The months with the highest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
The months with the lowest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).

Boulder, Colorado, USA

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