Juneau's climate is influenced primarily by the North Pacific Ocean and secondarily by the high, mountainous interior regions of northern British Columbia and the Yukon Territory. Much of the time, wet weather systems from the North Pacific are carried on westerly breezes (or gales!) through the waterways and across the islands of the Inside Passage. At times, high pressure systems in northern Canada bring strong winds, typically fair skies, and colder air in winter, warmer air in summer.
Juneau's climate is common to an area that extends from coastal British Columbia to northwest of Yakutat on the Gulf of Alaska. The entire area is home to the largest temperate rainforest in the world. Within the Southeast Alaska panhandle, the Tongass National Forest--largest in the United States--stretches for 500 miles. Dense forests of Sitka spruce and western hemlock on lower slopes of this mountainous region give way quickly to high alpine tundra and glacial ice. This landscape has provided Natives with abundant resources for thousands of years and the region now has highly magnetic appeal for both residents and visitors.
Normal summer temperatures are in the 50s and 60s Fahrenheit, occasionally hitting the 70s, and rarely the 80s. Normal winter temperatures are in the 20s and 30s, sometimes dipping into single digits or lower on wintry blasts from the interior.
Average annual precipitation is around 55 inches, with about 95 inches of snow annually, but microclimates are ubiquitous, resulting in significant increases or decreases in both temperature and precipitation within very short distances. For example, downtown Juneau--influenced more by the ocean--gets warmer temperatures and much more rain than the Mendenhall Valley just six miles away, which is influenced by a large glacier that extends to sea level from the 2,400-square-mile Juneau Icecfield.
On average, the driest months of the year are April and May and the wettest is October, with the warmest being July and the coldest January and February.
On summer solstice, the sun rises before 4 AM and sets after 10 PM for more than 18 hours of daylight, whereas it rises at nearly 9 and sets shortly after 3 on winter solstice for just over 6 hours of daylight. Spring months bring rapid change when Juneau sees an increase of more than half an hour of sunlight each week, and fall brings equally rapid change as sunlight diminishes at the same pace.