Western Regional Climate Center

PROVIDING CLIMATE SERVICES SINCE 1986

December in the West

Except for Montana, nearly the entire west observed above normal temperatures, especially SE New Mexico and the Front Range of Colorado. Alamosa, CO, tied its warmest December on record going back 63 years while Grand Junction, CO, had its warmest December since 1980. Fairbanks, AK, on the other hand, had its coldest December since 1980. Had it not been for extremely cold temperatures the final two days of the month many other locations would have possibly broken records for December warmth. Arizona recorded an unofficial new state record for the coldest all time temperature in December when an automated weather station near Flagstaff recorded -37 F (-38.3 C) on final hour of the 31st, breaking the old state record of -36 F (-37.8 C).

Precipitation was well above normal throughout the region except for Southern Arizona and New Mexico and Eastern Colorado. Many parts of southern and central California received their wettest December ever. It was the second wettest December on record in downtown Los Angeles dating back to 1889. Bishop, CA, received 105% of their annual average in 3 days (18-20th). Up to 29” of rain in the San Gabriel and San Bernardino Mountains of Southern California for the month, most of it within a 6-day period from the 17th-22nd. Bakersfield’s total of 5.82 inches (148 mm) not only broke a December record but an all time monthly record going back to 1893. New December records were also set in portions of Southern Nevada and Utah. St. George had their wettest December on record dating back 117 years. Over 15 inches (381 mm) of precipitation fell at Mt. Charleston, NV, while Ely recorded their wettest and snowiest December in 85 years of data. Snowpack in the Sierra Nevada of California was over 200% of normal by the end of the month and the rest of the west except Washington was reporting a snowpack of well over 100%. Meanwhile, in Honolulu, rainfall for the December was the greatest since 1987 (11.73 inches, 298 mm) and amounted to 67% of their 2010 annual total. Much of that fell in one day (5.41 inches, 137 mm) on the 19th.

Significant Events for December 2010

December 11-14: Heavy Rain and Strong Winds in Washington: A very warm and moist storm hit the Pacific Northwest. Rainfall totals were between 3 and 8 inches (76-203 mm) in NW Washington with some isolated area of the Olympic Peninsula measuring up to 12 inches (305 mm). Localized urban and small stream flooding occurred while service on Amtrak was cancelled from Portland, OR, to Vancouver, Canada, for nearly 48 hours due to numerous landslides. A 55-year old woman was killed in the early morning hours of the 14th near Port Orchard, WA, when strong winds toppled a tree on to her house while she slept.

December 17-22: Heavy Rain and Snow in California: Beginning on Friday the 17th one of the more powerful Pacific storms to hit California and the Southwest in the past six years caused extensive damage throughout the region. Six days of heavy rain triggered rock and mudslides, large scale flooding, evacuations and road closures throughout the four states of California, Nevada, Utah and a portion of Arizona. In Southern California, a 20-mile stretch of Highway 1 between Malibu and Oxnard was closed on the 21st after a rock and mudslide. Amtrak service was also disrupted between San Diego and San Juan Capistrano due to mudslides and flooding. As many as 70 homes were buried in over four feet of mud near San Bernardino and over 200 homes were evacuated. One death was confirmed in Riverside County when a woman who drove into a flooded crossing was swept away. According to AAA, more than 25,000 motorists called for help on the 20th, the largest number ever in a 24-hour period. A state of emergency was declared for 6 counties in southern California and damage is estimated at over $10 million. In Mission Valley, near San Diego, 900 residents were forced from their homes from flooding. In Southern Nevada, Northwest Arizona and Southwest Utah record rainfall and flooding occurred over the region. Six homes were swept away in Beaver Dam Wash, AZ, with another six suffering severe damage. The Virgin and Santa Clara Rivers flooded, destroying several holes of the Southgate Golf Course in St. George. Significant rockfalls in Zion National Park forced a closure of the park. Several roadways and intersections in Las Vegas were closed due to flooding.

December 29-31: Strong Winter Storm: A strong cold front moved through the entire west on the final three days of the month causing very cold temperatures, heavy snow and strong winds. Two feet of snow and 100 mph winds were recorded in the Sierra Nevada followed by an extreme drop in temperature. A snowboarder died from exposure when she got lost at a California ski area. Local flooding from heavy rain was reported in southwest Oregon and southern California. A 70-year old woman was killed at the Safari West Preserve near Santa Rosa, CA, when an oak tree was uprooted and fell on the frame tent she was staying in.

December 2010 Departure from Normal Temperature and Percent of Normal Precipitation for Western United States

Departure from normal temperature Departure from normal precipitation

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