The Climate of Boulder, Colorado

Boulder is located in north-central Colorado at the base of the Rocky Mountains, about 25 miles northwest of Denver. With an elevation of 5,430 feet above sea level, Boulder enjoys a semi-arid climate with four distinct seasons.

Overview of Boulder’s Climate

Boulder has a mild, dry climate characterized by sunny days, low humidity, and cool nights. Summers in Boulder are warm with daytime highs in the 80s and occasional heat waves pushing temperatures into the 90s. Winters are generally cold and snowy with highs in the 40s. Boulder receives lots of sunshine year-round with an average of 300 days of sun per year.

The climate is influenced by Boulder’s location on the edge of the Rocky Mountains. The mountains block humid air from the Gulf of Mexico, keeping summers dry. Boulder also benefits from a rain shadow effect, resulting in only about 20 inches of precipitation annually. The low humidity allows for large daily temperature swings.

Spring Weather in Boulder

Spring is a transitional season in Boulder with increasing temperatures and a mix of rain and snow showers.

March

• Average high: 55°F
• Average low: 30°F
• Precipitation: 1.7 inches of rain/snow

March marks the beginning of spring in Boulder. Daytime highs reach into the 50s while overnight lows are still cold in the 30s. As the snowpack melts, March is one of the wetter months with rain and snow showers.

April

• Average high: 63°F
• Average low: 35°F
• Precipitation: 2.2 inches rain/snow

April brings warmer temperatures with highs climbing to the low 60s. As snow gives way to rain showers, precipitation increases to 2.2 inches. Trees begin to bud and wildflowers start to bloom.

May

• Average high: 71°F
• Average low: 44°F
• Precipitation: 2.8 inches

May feels like spring in Boulder with mild temperatures and longer daylight hours. Highs reach the low 70s while lows drop to the 40s. Snow is rare this time of year with 2-3 inches of rain typical. Spring wildflowers are in peak bloom.

Summer Weather in Boulder

Summers in Boulder are warm, dry, and sunny. June through August are the warmest months.

June

• Average high: 81°F
• Average low: 51°F
• Precipitation: 1.7 inches

June starts off summer with daily high temperatures climbing into the 80s. Humidity remains low and overnight lows drop into the 50s. Boulder receives occasional thunderstorms in June, contributing 1.7 inches of rain.

July

• Average high: 86°F
• Average low: 57°F
• Precipitation: 1.8 inches

July is the hottest month in Boulder with average highs of 86°F. Low temperatures stay mild in the upper 50s. Brief afternoon thunderstorms provide a little relief from the heat and add 1.8 inches of rainfall.

August

• Average high: 83°F
• Average low: 56°F
• Precipitation: 1.9 inches

August is still hot with daily highs in the mid-80s but temperatures start to decrease by the end of the month. Overnight lows dip into the mid-50s. Thunderstorms are common, especially late in the month, with 1.9 inches of precipitation.

Fall Weather in Boulder

Fall brings comfortable warm days and cool nights to Boulder. It’s a great time to enjoy the changing fall foliage.

September

• Average high: 77°F
• Average low: 46°F
• Precipitation: 1.7 inches

September ushers in fall with high temperatures in the upper 70s. Overnight lows drop into the 40s. Rain showers are common with 1.7 inches of precipitation. Tree leaves start changing from green to gold.

October

• Average high: 67°F
• Average low: 36°F
• Precipitation: 1.4 inches

October brings cooler fall weather with highs around 67°F and lows down to 36°F. Rain showers continue with 1.4 inches on average. Aspen trees cloak the mountains in vibrant yellow and orange leaves.

November

• Average high: 53°F
• Average low: 26°F
• Precipitation: 1.1 inches

November ends the fall season with declining temperatures. Highs reach the low 50s while overnight lows drop below freezing into the mid-20s. Snow showers become more likely with 1.1 inches of precipitation.

Winter Weather in Boulder

Boulder winters are cold and snowy. From December to February, expect freezing temperatures, snowstorms, and plenty of sunshine between storms.

December

• Average high: 44°F
• Average low: 18°F
• Precipitation: 1.5 inches

December is the start of winter in Boulder with high temperatures in the 40s and lows around 18°F. Boulder averages 8 inches of snow in December contributing to 1.5 inches of precipitation. Holiday snowstorms are common.

January

• Average high: 43°F
• Average low: 17°F
• Precipitation: 1.1 inches

January is one of the coldest months in Boulder. Daytime highs hover in the low 40s while overnight lows plummet to 17°F. About 7 inches of snow falls in January with 1.1 inches of precipitation total. Sunny skies prevail between winter storms.

February

• Average high: 46°F
• Average low: 20°F
• Precipitation: 1.3 inches

February continues winter in Boulder with below-freezing temperatures. Highs reach the mid-40s and lows average around 20°F. Snowstorms deposit 8 inches of snow adding to the 1.3 inches of precipitation. Sunshine increases toward the end of winter.

Climate Data for Boulder, CO

Below is a table summarizing key climate data for Boulder, CO including average temperatures, precipitation, and extreme records.

Month	Average High	Average Low	Avg Precipitation	Record High	Record Low
January	43°F	17°F	1.1 inches	75°F (1954)	-24°F (1913)
February	46°F	20°F	1.3 inches	78°F (1986)	-27°F (1951)
March	55°F	30°F	1.7 inches	82°F (2003)	-21°F (1957)
April	63°F	35°F	2.2 inches	89°F (1986)	10°F (1975)
May	71°F	44°F	2.8 inches	93°F (1991)	21°F (1957)
June	81°F	51°F	1.7 inches	103°F (1954)	30°F (1919)
July	86°F	57°F	1.8 inches	104°F (2005)	41°F (1897)
August	83°F	56°F	1.9 inches	102°F (2020)	36°F (1918)
September	77°F	46°F	1.7 inches	101°F (2013)	20°F (1936)
October	67°F	36°F	1.4 inches	90°F (1963)	-4°F (1917)
November	53°F	26°F	1.1 inches	82°F (1986)	-18°F (1916)
December	44°F	18°F	1.5 inches	75°F (1939)	-27°F (1924)

How Altitude Impacts Boulder’s Climate

Boulder’s elevation at over a mile above sea level plays a major role in its climate patterns. Here are some of the effects of altitude on Boulder weather:

• Colder temperatures – Boulder experiences lower average temperatures than nearby Denver, located at 5,280 feet, due to the higher elevation. Air temperature drops approximately 3.5°F for every 1,000 feet gained in elevation.
• Increased UV exposure – At higher elevations, there is less atmosphere for UV rays to pass through. This results in increased solar radiation and heightened risk of sunburn in Boulder.
• Lower air pressure – Thinner air at altitude results in lower air pressure. This allows moisture to evaporate more readily contributing to the low humidity.
• Enhanced precipitation – The Rocky Mountains force air upward resulting in adiabatic cooling and condensation. This leads to increased rainfall and snowfall on the windward side of the mountains where Boulder sits.
• Later freeze dates – Despite colder average temperatures, freeze dates come later in fall and earlier in spring at higher elevations. This lengthens the frost-free growing season in Boulder.
• Increased snowfall – Boulder receives more snowfall than lower elevation cities. The higher altitude leads to lower freezing levels allowing more precipitation to fall as snow.

Typical Sky Conditions in Boulder

Boulder enjoys sunny skies for most of the year. Here are some patterns in Boulder’s typical sky conditions:

Sunny, Clear Skies

• Over 300 days of sun per year
• Driest weather occurs June-August
• Crisp, cold days in winter have abundant sunshine between storms
• Excellent visibility year-round due to low humidity

Partly Cloudy

• Spring and fall see increasing cloud cover
• Brief thunderstorms in summer add cloud build up
• Transitional weather in March and April means more cloudy periods

Cloudy and Gray

• Winter storm systems can bring dense cloud cover
• The wettest months of May and July have more cloudy days
• Increasing fall storm systems in October and November add clouds

Rain and Snow Showers

• Spring rain/snow showers: March-April
• Summer thunderstorms: July-August
• Fall rainstorms likely: September-November
• Snowstorms occur: October-April

Weather Hazards in Boulder

While Boulder’s climate is generally mild, it is prone to some hazardous weather conditions:

Late Spring Snowstorms

Spring snowstorms can occur in Boulder as late as April bringing heavy, wet snow that downs trees and causes power outages. The foothills are especially impacted.

Flash Flooding

Sudden downpours cause flash flooding of creeks and low-lying areas. Burn scars from wildfires increase flood risk.

Hail Storms

Summertime thunderstorms often produce large, damaging hail. Hail exceeds 1 inch diameter at least once per year.

Wildfires

Forested areas near Boulder have an elevated wildfire risk, especially in drought years. Wildfire smoke can degrade air quality.

Tornadoes

Weak tornadoes occasionally develop within summer thunderstorms. The eastern plains have the highest tornado risk.

Blizzards

Major winter storms with heavy snow and wind create blizzard conditions mainly from October-April. Travel becomes extremely dangerous.

Heat Waves

Boulder can experience hot temperatures above 90°F for several days in a row, especially in July. This poses health risks.

How to Dress for Boulder’s Weather

Boulder’s variable seasonal weather requires dressing in layers you can add or remove. Here are some tips:

Daily Staples

• Lightweight shirts and pants
• Fleece jacket or sweater
• Comfortable walking shoes or sneakers
• Sunglasses and sunscreen

Spring

• Light jacket and layers for fluctuating temperatures
• Rain jacket and umbrella
• Light gloves and hat

Summer

• Lightweight, breathable fabrics
• Hat and sunglasses for sun protection
• Sandals or hiking shoes
• Swimwear and sunscreen

Fall

• Light to mid-weight jackets and layers
• Waterproof boots and shoes
• Scarf, beanie/hat for warmth

Winter

• Heavy coat, hats, gloves, and scarf
• Waterproof, insulated boots
• Thermal base layers
• Snow pants and jacket for activities

How Climate Change is Impacting Boulder

Climate change is causing noticeable shifts in Boulder’s weather patterns:

• Higher temperatures – Average annual temperatures have risen 2°F in the past 50 years and are projected to keep increasing.
• More frequent heat waves – Heat waves above 90°F are becoming more common, especially in summer.
• Drier conditions – Decreasing precipitation trends have led to more drought.
• Reduced snowpack – Warming winters have resulted in less snowfall and smaller snowpack.
• Earlier snowmelt – With warming spring temperatures, spring runoff peaks 4-9 days earlier than it did in the 1980s.
• More frequent wildfires – Hotter, drier conditions have increased wildfire activity and length of fire season.
• Greater flood risk – Fire burn scars near Boulder now increase the likelihood of flash flooding.

How to Enjoy Boulder’s Weather

Boulder’s mild climate lends itself to year-round outdoor recreation. Some activities to enjoy by season:

Spring

• Hiking – Enjoy wildflowers and warmer temps on trails
• Cycling – Cooler temperatures ideal for biking
• Whitewater rafting – Rapid snowmelt creates rapids

Summer

• Mountain biking – Ride the extensive singletrack trails
• Rock climbing – Climb the iconic Flatirons formations
• Patio dining – Eat outside at a restaurant with mountain views

Fall

• Leaf peeping – See golden fall foliage in the mountains
• Apple picking – Harvest apples at local orchards
• Camping – Crisp evenings and color tours at campgrounds

Winter

• Skiing – Downhill and cross-country skiing at Eldora ski area
• Snowshoeing – Explore forest trails on snowshoes
• Ice skating – Enjoy public ice rinks around town

So in summary, Boulder enjoys a mild, dry climate with four distinct seasons and ample sunshine. The weather supports an active, outdoor lifestyle year-round. While facing some climate change impacts, Boulder remains one of the most desirable places to live in Colorado.