Climate and monthly 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

The climate of Boulder

Perched on the east side of the Rocky Mountains, Boulder, Colorado, is situated in the mid-latitude steppe of the Köppen climate classification. Its predominate climate is classified as BSk, which indicates cold and semi-arid weather patterns. Boulder endures a fusion of weather conditions across every season, making it a pleasant city to experience a rotation of climates.

Throughout the year, the highs in Boulder reach a peak of 80.4°F (26.9°C) in July, followed closely by 79.5°F (26.4°C) in August. On the other end of the spectrum, temperatures plunge to a chilling 19°F (-7.2°C) in January and 18°F (-7.8°C) in February. On average, relative humidity ranges from 45% in the months of June to September to a damp 70% in February. Precipitation is also spread out in the course of the year, with the highest rainfall of 2.48" (63mm) measured in May. During the winter, monthly snowfall can reach up to 7.76" (197mm) in April, offering plenty of opportunities for winter activities.

The daylight hours increase as the year progresses, starting from 9.7 hours in January to eventually coincide with the solstice in June at 15 hours. Following this peak, there is a gradual decrease to the minimum in December at 9.4 hours.

The best time to visit Boulder

For those planning to visit Boulder, the months from May to September provide versatility in terms of weather, daylight, and outdoor activities. In this time period, the temperature skirts between 52.3°F (11.3°C) to a delightful 80.4°F (26.9°C), inducing the landscape to bloom with lushness. With an average highest rainfall of just 2.48" (63mm) in May, the city experiences a dampened heat that gives way to the bliss of summer.

The worst time to visit Boulder

Balancing the pleasures of its warm season, Boulder exhibits a bitter cold in the winter months. The harshness of this season, from December to February, is punctuated by low temperatures that dip to a frigid 19°F (-7.2°C) and snowfall that frequently tops up to 5.83" (148mm). Superimposed with reduced daylight hours that hit a low of 9.4 hours, it becomes unappealing for outdoor activities and sightseeing.

Spring weather in Boulder

Spring in Boulder sets in with a slight chill, as March typically begins with a high of 46.4°F (8°C), eventually climbing to reach 61°F (16.1°C) by May. The season is marked by an uptick in humidity, with levels hovering around 58% on average. This is often accompanied by the wettest days of the year, with rainfall levels peaking at 2.48" (63mm) in May. Despite this, spring presents an increase in daylight hours, offering ample time for outdoor activities.

Summer weather in Boulder

Delightful summer days in Boulder are characterized by temperatures that scale to a high of 80.4°F (26.9°C) in July, sustaining the warmth until August with a high of 79.5°F (26.4°C). While the humidity drops to about 45%, the city experiences lighter rainfall during these months, typically ranging between 1.5" (38mm) and 1.89" (48mm). The generous daylight hours, peaking at 15 hours in June, invite a host of outdoor events and activities.

Autumn weather in Boulder

Autumn introduces Boulder to a gentle coolness, as the high temperatures drop from 72.3°F (22.4°C) in September to a milder 57.2°F (14°C) in October. While humidity subtly increases to 51% on average, the area's rainfall continues to decline, settling at 0.91" (23mm) in October. The welcome decrease in heat and the lingering daylight hours still allow for enjoyable outdoor undertakings.

Winter weather in Boulder

Winter in Boulder ushers in a shift to cold weather, with December having temperatures between 19°F (-7.2°C) to 35.2°F (1.8°C). The snowfall frequently reaches its peak in this period, with amounts sometimes amounting up to 5.83" (148mm) in February. The plummeting temperatures are accompanied by shorter daylight hours, decreasing to 9.4 hours in December. Despite the unforgiving cold, it becomes a haven for winter sports' enthusiasts.

Weather in January

In Boulder, Colorado, January brings the year's chilliest weather. The month commences with colder average temperatures, reaching a high approximately of 36.7°F (2.6°C) and plummeting to lows approximately of 19°F (-7.2°C). Weather in January »

Weather in February

Boulder's February weather is marked by an upward push in temperature, making it slightly warmer than January. The increased warmth is paired with amplified snowfall up to 5.83" (148mm). These weather conditions, coupled with longer daylight hours, contribute to a more pleasant ambience when compared to the previous month. Weather in February »

Weather in March

March signifies the advent of spring in Boulder, instigating a marked shift in climate. Temperatures start to climb, establishing the basis for the ensuing warmer months. This month receives maximum snowfall of about 6.26" (159mm), marking the last significant flurry before the arrival of summer. Weather in March »

Weather in April

With the arrival of April, Boulder embraces the full potential of spring, leaving behind the heavy snowfall of March. This period of the year is typified by a further rise in temperature and more frequent rainfall, tallying at approximately 1.65" (42mm). Weather in April »

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. Weather in May »

Weather in June

Boulder warmly welcomes summer with the arrival of June, presenting an overall break from the dampness of May. The city indulges in warm temperatures, longer sunshine hours and lower chances of rain, making the city's outdoor lifestyle much more enticing. Weather in June »

Weather in July

July is the peak of summer in Boulder, offering the highest temperatures of the year. The city's atmosphere becomes infused with summer vibes due to high temperatures, hitting highs around 80.4°F (26.9°C) and lows around 55.2°F (12.9°C). Weather in July »

Weather in August

In Boulder, August is the last full summer month, characterized by sustained warmth and decreasing rainfall. Though it mirrors much of July's warmth, a slight dip in temperature indicates the upcoming autumn. The wind velocity typically averages around 5.7mph (9.2km/h) in August, ushering in cooler evenings. Weather in August »

Weather in September

As Boulder transitions to fall in September, a significant decline in temperature begins. This month provides a respite from the intense summer heat while still providing plenty of sunshine. Snowfall makes a reappearance but only in trace amounts, setting the stage for the colder months ahead. Weather in September »

Weather in October

October brings with it cooler temperatures and the full onset of autumn in Boulder. The month is fitting for outdoor activities, with clear skies, optimal visibility, and less intense sunshine. The city's rainfall drops to approximately 0.91" (23mm), just as winter starts making its presence felt with a slight surge in snowfall. Weather in October »

Weather in November

Boulder experiences significant transitions in weather during November, with clear signs of the impending winter. Snowfall marginally increases, painting the city in light winter shades, making it a transformational period from autumn to winter. Weather in November »

Weather in December

December in Boulder signs off the calendar year with full blown winter. The city welcomes stringent cold, with frequent encounters of snowfall amounting up to approximately 3.94" (100mm). Temperatures plunge to their yearly lows in line with the season, with daylight hours reaching a dwindling stage. Weather in December »
Updated: Feb 10, 2024
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate

Frequently asked questions

What is the driest month in Boulder?

January is the month with the least rainfall. Rain falls for 4.3 days and accumulates 0.39" (10mm) of precipitation.

How much does it rain in Boulder?

In Boulder, Colorado, during the entire year, the rain falls for 117.3 days and collects up to 14.17" (360mm) of precipitation.

When does it snow in Boulder?

Months with snowfall are January through May, October through December.

How many days does it snow in Boulder?

Throughout the year, in Boulder, Colorado, there are 44.8 snowfall days, and 37.01" (940mm) of snow is accumulated.

When is the lowest UV index in Boulder?

The months with the lowest UV index are January, February, November and December, with an average maximum UV index of 2.

What is the most humid month in Boulder?

With an average relative humidity of 70%, February is the most humid month in Boulder.

What is the month with the least sunshine in Boulder?

The month with the least sunshine in Boulder, Colorado, is February, with an average of 6.6h of sunshine.

When is Daylight Saving Time (DST) in Boulder?

On Sunday, March 10. 2024, at 2:00 am, Daylight Saving Time starts in Boulder, Colorado, and the time zone changes from MST to MDT. Daylight Saving Time ends Sunday, November 3. 2024, at 2:00 am, and the time zone reverts from MDT to MST.

What is the snowiest month in Boulder?

The month with the most snowfall in Boulder is April, when snow falls for 4.9 days and typically aggregates up to 7.76" (197mm) of snow.

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.

What is the least humid month in Boulder?

June, August and September, with an average relative humidity of 45%, are the least humid months.

When it does not snow in Boulder?

In Boulder, Colorado, snow does not fall in June through September.

When are the longest days in Boulder?

With an average of 15h and 0min of daylight, June has the longest days of the year in Boulder, Colorado.

What are the months with the most sunshine in Boulder?

June and July, with an average of 11.7h of sunshine, are months with the most sunshine.

When is the highest UV index in Boulder?

The months with the highest UV index are June through August, with an average maximum UV index of 5.

What part of the year is the hottest in Boulder?

Boulder's warmest month, July, generally records average temperatures ranging from a high of 80.4°F (26.9°C) to a low of 55.2°F (12.9°C).

What is the coldest time of year in Boulder?

The coldest period tends to be December, when average temperatures fluctuate between a high of 35.2°F (1.8°C) and a low of 18.1°F (-7.7°C).

What is the month with the shortest days in Boulder?

December has the shortest days of the year in Boulder, with an average of 9h and 24min of daylight.

Average temperature
Boulder, CO

Average temperature - Boulder, CO

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).

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
Boulder, CO

Average pressure - Boulder, CO

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
Boulder, CO

Average wind speed - Boulder, CO

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
Boulder, CO

Average humidity - Boulder, CO

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
Boulder, CO

Average rainfall - Boulder, CO

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
Boulder, CO

Average rainfall days - Boulder, CO

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
Boulder, CO

Average snowfall - Boulder, CO

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
Boulder, CO

Average snowfall days - Boulder, CO

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 / Average sunshine
Boulder, CO

Average daylight / Average sunshine - Boulder, CO

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).

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
Boulder, CO

Average sunshine days - Boulder, CO

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
Boulder, CO

Average UV index - Boulder, CO

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 visibility
Boulder, CO

Average visibility - Boulder, CO

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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