Fairbanks, Alaska - Geography - Climate

Climate

Fairbanks’ climate is usually classified as subarctic (Köppen Dfc), with long, cold winters, and short, warm summers, in which much of the annual precipitation falls. In Fairbanks, winter lasts from late September/early October until late April/early May. October through January are the snowiest, and snow is limited from February to May. On average, the season's first snow falls in Fairbanks on September 21 and the first inch of snow accumulates by October 8. The snowpack is established by October 18, on average, and remains until May. Snow occasionally arrives early and in large amounts. On September 13, 1992, 8 inches (20 cm) of snow fell in the city, bending trees still laden with fall leaves. That September also was one of the snowiest on record, as 24 inches (61 cm) fell, compared to an average of 2.2 inches in the month. Average winter low temperatures range from −15 °F (−26 °C) to −25 °F (−32 °C), but extremes can range from 50 °F (10 °C) to −60 °F (−51 °C). In summer, temperatures typically range between 70 °F (21 °C) and 50 °F (10 °C); Fairbanks did not record a 90 °F (32 °C) temperature between 1994 and 2009. The highest recorded temperature in Fairbanks was 96 °F (36 °C), while the lowest was −62 °F (−52 °C). The warmest year in Fairbanks was 1981, when the average annual temperature was 32.0 °F (0.0 °C). The coldest year was 1956, whose average annual temperature was 21.3 °F (−5.9 °C). Record low temperatures below 0 °F (−17.8 °C) have been recorded in every month except June, July, August, and September.

These widely varying temperature extremes are due to three main factors: temperature inversions, daylight, and wind direction. In winter, Fairbanks’ low-lying location at the bottom of the Tanana Valley causes cold air to accumulate in and around the city. Warmer air rises to the tops of the hills north of Fairbanks, while the city itself experiences one of the biggest temperature inversions on Earth. Heating through sunlight is limited because of Fairbanks's high-latitude location. At the winter solstice, Fairbanks experiences 3 hours and 43 minutes of sunlight. At the summer solstice, Fairbanks receives 21 hours and 49 minutes of direct sunlight; after sunset, twilight is bright enough to allow daytime activities. During winter, the direction of the wind also causes large temperature swings in Fairbanks. When the wind blows from any direction but the south, average weather ensues. Wind from the south can carry warm, moist air from the Gulf of Alaska, greatly warming temperatures. When coupled with a chinook wind, temperatures well above freezing often result.

In addition to the chinook wind, Fairbanks experiences a handful of other unusual meteorological conditions. In summer, dense wildfire smoke accumulates in the Tanana Valley, affecting the weather and causing health concerns. When temperature inversions arise in winter, heavy ice fog often results. Ice fog occurs when air is too cold to absorb additional moisture, such as that released by automobile engines or human breath. Instead of dissipating, the water freezes into microscopic crystals that are suspended in the air, forming fog. Fairbanks’ most notable unusual meteorological occurrence is the prevalence of the aurora borealis, commonly called the northern lights, which are visible on average more than 200 days per year in the vicinity of Fairbanks.

Since 1949 Fairbanks's average winter temperature has risen by 7.7 °F (4.3 °C), average spring temperature by 3.8 °F (2.1 °C), and its average summer temperature by 2.3 °F (1.3 °C). During the same period, Fairbanks' average autumn temperature has fallen by 0.4 °F (0.2 °C). If only the years 1977–2008 are considered, Fairbanks’ average annual temperature has dropped by 1.3 °F (0.7 °C).