December in the West
Much of the West saw above normal precipitation for the month of December, with the main exceptions being Washington, interior Montana and coastal sections of California and Oregon. The Pacific Northwest and northern Rockies experienced well below normal temperatures, while temperatures in much of Arizona and New Mexico were well above average.
December was an active weather month over the West characterized by a persistent stronger than normal jet stream over the northern half of the US and two major atmospheric river events during the first half of the month. These were both inland penetrating atmospheric rivers that brought widespread heavy rain and snowfall from California all the way to the Rocky Mountains of Wyoming and Montana. Jackson, Wyoming, had its sixth wettest December since records began in 1905 with 3.22 in (81.79 mm), 210% of normal. Elko, Nevada had its eighth wettest December on record with 2.83 in (71.88 mm), 236% of normal. Records for Elko began in 1888. Above average precipitation was also found in the Sierra Nevada. Blue Canyon, California, received 15.39 in (390.91 mm), 134% of normal, This brought some improvement of drought conditions to the region; however, the warm nature of the atmospheric river storms produced high snow levels and snow water equivalent actually decreased in mid-to-low elevation locations over the course of the month. For example, the Tahoe Basin went from 119% of normal snow water equivalent on December 1st 2016 to 62% of normal on January 1st 2017.
Precipitation was generally below normal in Washington, most notably east of the Cascade Range. Ephrata, Washington, recorded 0.32 in (8.13 mm) of precipitation, 26% of normal. A small region in southwest Nevada, east of the White Mountains, did not benefit from the atmospheric river storms and reported drier than normal conditions. Dyer, Nevada, recorded only 0.08 in (2.03 mm) for the month, 24% of normal. A cold, and somewhat dry, continental polar air mass was in place over much of the Pacific Northwest and Montana during early and mid-December, producing below normal temperatures. Many locations had one of their top-10 coldest Decembers on record. Baker City, Oregon recorded its coldest December at 14.7 F (-9.6 C), 10.1 F (5.6 C) below normal. Records at Baker City date back to 1943. Great Falls, in north-central Montana, saw its 5th coldest December in an 80-year record at 14.3 F (-9.8 C), 10.5 F (5.8 C) below normal, Much of Arizona and New Mexico, as well as sections of coastal California observed above normal temperatures. Albuquerque, New Mexico, observed an average temperature of 49.7 F (9.8 C), 2.9 F (1.6 C) above normal, and San Diego, California, recorded 66.3 F (19.1 C), 2.4 F (1.3 C) above normal. Temperatures in Alaska were well below normal during the first half of the month and above normal the second half of the month. Interior and southern portions of the state were 3-6 F (1.7 C to 3.3 C) below normal, while the west coast and North Slope were 3-8 F (1.7-4.4 C) above normal. Temperatures at Utqiaġvik, on the North Slope, were 7.9 F (4.4 C) above normal, while at the other end of the spectrum, Kenai saw a departure of 6.1 F (3.4 C) below normal. December in Alaska was quite dry in the southern and southeastern portions of the state and for the Interior and North Slope precipitation was well above normal. Fairbanks led the way with 1.96 in (50 mm) precipitation, 306% of normal and the 4th wettest December since records began in 1904. Unlike previous winters, the precipitation in the mainland all fell as snow. In Hawaii, Maui and the Big Island experienced well above normal precipitation with Hana recording 19.4 in (492.8 mm), 278% of normal and the wettest December since records began in 1950. Oahu and Kauai saw significantly below normal precipitation; Lihue recorded 1.17 in (30 mm) rainfall, 23% of normal and the 10th driest December since records began in 1950.
Significant Events for December 2016
December 1-5: Hawaii's Big Island peaks see heavy snow: Up to 35 in (89 cm) of snow was reported on Big Island volcanic summits. Sections of Hawaii Volcanoes National Park were closed above Red Hill Cabin. December 7-8: Ice storm and low elevation snow in Oregon: A strong storm brought a wintery mix to low elevations of Oregon. Accumulating snow and up to 0.75 in (19 mm) of ice accumulation was reported in Portland leading to power outages, traffic accidents, and airport delays. December 9-10: Atmospheric river impacts Sierra Nevada and western Nevada: A warm winter storm brought heavy snow and then rain to the Sierra Nevada, with snow levels rising to over 8,000 ft (2400 m). This created dangerous avalanche conditions and one death was reported at the Mount Rose ski resort (skier was in a closed area) in Nevada. The Truckee River reached minor flood stage and minor flood impacts were reported in Truckee, California and around the Reno, Nevada area.