December in the West
In the West, storms brought well above normal precipitation to the Northwest, northern Great Basin, and some areas of the Rocky Mountains. Temperatures averaged near normal, with pockets of above normal temperatures along the northern tier.
The Pacific Northwest saw impressive amounts of precipitation. Portland, Oregon, observed its wettest December and all-time wettest month at 15.24 in (387 mm), 278% of normal. Portland also had its second wettest day on record on December 7, when 2.67 in (68 mm) of rain fell. Precipitation was observed in Portland each day from December 1-25, the second longest streak on record. January 1950 holds the record for longest precipitation streak at 29 days. Records for Portland began in 1938. Seattle, Washington, recorded 11.21 in (285 mm) for the month, the second wettest December in a 71-year record. McCall, Idaho, observed 7.69 in (195 mm) precipitation, 230% of normal, the 4th wettest December since records began in 1905. In the Great Basin, Ely, Nevada, logged 1.38 in (35 mm) of precipitation this month, 234% of normal, 12th wettest since records began in 1888. Pockets in the Rockies were wet as well. Hayden, Colorado, had its wettest December in a 111-year record with a total 6.68 in (170 mm) of precipitation, 415% of normal. Yosemite National Park observed 12.02 in (305 mm) of precipitation, 221% of normal and the 11th wettest since 1906. Many areas that observed above normal precipitation also saw significant snowfall. In southern Oregon, Crater Lake observed 196.7 in (500 cm) of snowfall, breaking the previous December snowfall record of 196 in (498 cm) set in 1948. Snoqualmie Pass in Washington observed its snowiest December on record at 193.3 in (491 cm) of snowfall, breaking the previous record of 192 in (488 cm) set in 1968. In the Colorado Rockies, Steamboat Springs received 66.9 in (170 cm) of snow this month, 174% of normal, 7th snowiest since records began in 1893. Snowpack in the Sierra Nevada was just slightly above normal at month’s end. In the Cascades and northern Great Basin, snowpack ranged from 100% to nearly 200% of normal. The northern and central Rockies observed slightly below normal snowpack, generally 75-100% of normal, while the southern Rockies were 110% to 150% of normal. Abundant precipitation and building snowpack helped to alleviate drought conditions in eastern Washington, western Oregon, coastal northern California and portions of Idaho and Montana. Extreme to exceptional drought conditions persisted California, western Nevada, and southeastern Oregon.
The Desert Southwest was seasonally dry this month. Las Vegas, Nevada recorded 0.01 in (<1 mm) for the month, 2% of normal. In Las Vegas’ 68-year record, 16 other years observed 0.01 in (<1 mm) or less. Southern California also saw drier than normal conditions; rainfall in Los Angeles totaled 0.57 in (14 mm), 24% of normal. Drought conditions improved in a very small area of western Arizona and northern Wyoming.
Temperatures averaged near normal across much of the West. A very cold system during the final week of the month brought temperatures 5-10 F (3-6 C) below normal across much of the West. Temperatures at a few locations across the northern tier of the region averaged above normal for December. In northeastern Washington, Chewelah recorded an average of 29.5 F (-1.4 C), 4.6 F (2.5 C) above normal. In northeastern Montana, temperatures in Glasgow averaged to 21.4 F (-5.8 C), 5.1 F (2.8 C) above normal.
Parts of Hawaii continued to remain warm. Lihue, Kauai, had its warmest December since records began in 1950, averaging 76.2 F (24.5 C), 3 F (1.6 C) above normal. Honolulu, Oahu, and Hilo, Big Island, both had their second warmest December on record at 77.9 F (25.5 C) and 74.6 F (23.7 C), respectively. After wetter than normal conditions the past 4 months, many locations in Hawaii observed a drier than normal December. Honolulu recorded 0.27 in (7 mm), 8% of the December normal, tied for 7th driest December in 76 years. In Alaska, temperatures were within 5 F (2.8 C) of normal. With the exception of the southeast, much of the state observed drier than normal conditions this month. Fairbanks received 0.07 in (2 mm) of precipitation, 11% of normal and the 5th driest December since records began in 1929. Anchorage recorded 0.23 in (6 mm), 21% of normal, the 4th driest since records began in 1952.
Significant Events for December 2015
December 7-9: Flooding in western Oregon and Washington: Following a wet first week of the month, a winter storm with abundant subtropical moisture brought over 4+ in (100+ mm) of rain over a 2-day period. The heavy rains produced flooding along creeks and rivers, landslides, downed trees and power outages. Many roads in the region were closed due to landslides, disrupting travel. In Portland, Oregon, the sewer system flooded and outflowed into the Willamette River and Columbia Slough. December 25: Solimar Fire burns in southern California: Strong winds caused power lines to arc, igniting the Solimar Fire near Ventura, California. The fire burned 1,200 acres (486 hectares) and caused temporary closure of Highway 101. The fire could cause debris flows with coming rains. December 30: Disaster declared in Kootenai County, Idaho, due to snow accumulation: Kootenai County received significant snowfall this month. Coeur d’Alene observed 25 in (64 cm), more than twice its normal December snowfall. The snow placed heavy loads on trees and structures, causing branches to snap resulting in damage to several homes.