Juneau Weather Guide: Climate in Alaska's Coastal Rainforest

The Rhythm of the Coastal Rainforest

Juneau’s weather is defined by its position within the Tongass National Forest, the world’s largest temperate rainforest. Unlike the harsh, dry cold of interior Alaska, Juneau experiences a maritime climate moderated by the North Pacific Ocean. This results in relatively mild temperatures year-round, but also leads to persistent cloud cover and frequent precipitation. Statistically, Juneau sees measurable rain or snow on roughly 230 days of the year, creating a landscape that is perpetually lush, misty, and green.

Daily Climate Behavior

In Juneau, the weather is rarely static. A typical day often begins with "marine layer" clouds or low-hanging mist that clings to the sides of Mount Juneau and Mount Roberts. Because the city is nestled in a topographical bowl between steep peaks and the Gastineau Channel, moisture often gets trapped, leading to sudden shifts between light drizzle and brief bursts of sunlight. This phenomenon, which locals often call "liquid sunshine," means that clear blue skies can transition to a dense grey ceiling within thirty minutes. Evening temperatures rarely drop drastically from daytime highs due to the insulating effect of the cloud cover and the thermal mass of the surrounding waters.

Seasonal Trends

• Spring (March – May): Known as the "dry season," spring is historically the sunniest time of year. While temperatures remain cool (35°F to 50°F), the rapidly increasing daylight—gaining roughly five to seven minutes per day—energizes the region. This is when the "breakup" occurs, as mountain snow begins to melt into local salmon streams.
• Summer (June – August): Summers are mild and damp. Average highs hover in the low 60s, though rare "heatwaves" can push temperatures into the upper 70s or 80s. The summer solstice brings over 18 hours of daylight, which locals maximize with late-night hiking and fishing, even if it is drizzling.
• Fall (September – November): This is the wettest season. Atmospheric rivers—plumes of moisture from the tropics—frequently hit the Panhandle, bringing heavy rain and gale-force winds. September is often the rainiest month, seeing over 9 inches of precipitation at the airport and significantly more in the downtown area.
• Winter (December – February): Winters are long and dark, with only six hours of daylight in late December. However, temperatures are surprisingly moderate, often hovering near the freezing mark (28°F to 35°F). This leads to a "snow-to-rain" cycle where heavy snowfalls are frequently washed away by warm Pacific rain just days later.

Microclimates and Variations

Juneau is a city of distinct microclimates. There can be a 5-to-10-degree temperature difference between the wind-whipped Gastineau Channel and the sheltered Mendenhall Valley.

• Downtown vs. The Valley: Downtown Juneau is more influenced by the ocean; it receives significantly more rain (up to 90 inches annually) and less snow. The Mendenhall Valley, influenced by the cold air drainage from the Mendenhall Glacier, is often several degrees colder and receives more accumulated snow (up to 86 inches at the airport).
• The Ridges: Alpine areas like the Eaglecrest Ski Area experience a completely different climate, often staying below freezing for months and receiving over 300 inches of snow while the city below remains in a rain-cold fog.

Weather Phenomena: Taku Winds and Atmospheric Rivers

One of Juneau’s most unique weather events is the Taku Wind. These are powerful downslope windstorms that occur when cold, dense air from the Canadian interior spills over the coastal mountains. Specifically affecting the downtown and Douglas areas, these winds can reach hurricane force (70–100 mph), even when the rest of the city is calm.

Additionally, the region is a primary target for Atmospheric Rivers. These moisture-laden storm systems can drop several inches of rain in 24 hours, occasionally causing localized flooding and landslides due to the steep, saturated terrain.

Historical Context and Local Adaptation

Historically, Juneau’s climate was slightly colder with more consistent winter snowpack. In recent decades, the city has seen a trend toward wetter, warmer winters where precipitation falls increasingly as rain rather than snow at sea level.

Locals have adapted to this permanent dampness with a "business as usual" attitude toward rain. In Juneau, outdoor activities—hiking, mountain biking, and even weddings—proceed regardless of the forecast. The city's architecture reflects this, with many downtown buildings featuring covered walkways (overhangs) to allow pedestrians to shop and move without constant exposure to the drizzle.

What It "Feels Like"

Beyond the thermometer, Juneau weather is defined by its humidity. A 40°F day in Juneau feels significantly colder than a 40°F day in a dry climate because the moisture-laden air pulls heat away from the body more quickly. Conversely, the "warmth" of a 65°F summer day feels intense under the high-latitude sun. There is a tactile quality to the air—it often smells of salt, pine needles, and wet earth, a sensory signature of the Pacific Northwest rainforest.