December in the West
A series of storms brought beneficial precipitation to drought-stricken areas such as California, eastern Oregon, southern Idaho, and the Great Basin this month. Throughout the West, temperatures averaged above normal despite an outbreak of very cold air over the last few days of the month. Average December temperatures across much of the West were more than 3 F (1.6 C) above normal. The greatest departures from normal average temperature were observed in southern Idaho and surrounding areas. Pocatello, Idaho recorded an average 32.2 F (0.1 C) for the month, the 7th warmest December in a 76-year record. To the south, Salt Lake City recorded a December average of 37.3 F (2.9 C), 7 F (3.8 C) above normal. This was the 3rd warmest December in Salt Lake since records began in 1928. Near the Idaho-Oregon border, Ontario, Oregon, observed an average of 36.2 F (2.3 C) this month, 8.4 F (4.6 C) above normal and the 3rd warmest since records began in 1945. Further west, average temperatures in California were also well above normal. In California’s Central Valley, Fresno recorded its warmest December in a 67-year record with an average 51.9 F (11.0 C). This was also the warmest calendar year on record at Fresno. In northern California, Mount Shasta observed an average 41.1 F (5.1 C), 6.0 F (3.3 C) above normal and the 2nd warmest December since records began in 1948. Calendar year 2014 was by a very large margin (1.8 F/1.0 C) the warmest on record since 1895 for California (61.5 F/16.4 C), also warmest for Arizona (62.3 F/16.8 C), and Nevada (53.0 F/11.7 C), and the second warmest for Oregon (49.6 F/9.8 C). Several areas of the West received above normal precipitation this month. A series of storm systems during the first half of the month brought significant precipitation to California and the Pacific Northwest and helped to alleviate drought conditions in localized areas. San Francisco recorded 11.7 inches (297 mm) this month, 257% of normal and the 5th wettest December in a 166-year record. Further south, Monterey, California observed its wettest December on record with 8.9 in (226 mm). This is 380% of normal and 2.76 in (70 mm) greater than the previous record set in 2002. Records at Monterey began in 1968. In southern California, San Diego recorded 4.5 in (114 mm), 294% of normal and the 6th wettest in a 76-year record. Unfortunately, snow levels were generally high during these storms thus did not contribute significantly to the development of Sierra Nevada and Cascade snowpack. At month’s end, Sierra Nevada snow water equivalent (SWE) stood at 40-60% of normal. The southern Cascades were generally in the 30-40% of normal SWE range. The northern Cascades saw SWE values in roughly the 40-70% of normal range. Further east, mountain ranges of the northeastern Great Basin and the Rocky Mountains ended the month with near to above normal SWE. Many locations in the Rocky Mountain states also recorded above normal precipitation this month. Helena, Montana logged 0.81 in (21 mm), 203% of normal and 12th wettest in a 77-year record. In central Wyoming, Lander recorded 1.82 in (46 mm) precipitation. This is 313% of normal and the 2nd wettest since records began in 1946. The Southwest saw areas of above normal precipitation as well. Flagstaff, Arizona observed 3.44 in (87 mm) this month, 184% of normal. Despite above normal precipitation in many areas this month, 54% of the West is experiencing moderate to exceptional drought. A large area of drought improvement was seen in northern California this month as well as small areas of improvement elsewhere in California, Oregon and Washington. Extreme to exceptional drought persists in a large area of California, western Nevada, and southeast Oregon. Precipitation across Hawaii was generally below normal. In southwestern Oahu, Kalaeloa received 0.76 in (19 mm) precipitation, 22% of normal. On the Big Island, Hilo received 6.10 in (155 mm), 53% of normal. At month’s end, 29% of the state was abnormally dry and 3% was in moderate drought. Further north, temperatures throughout Alaska were warmer than normal. The greatest departures from normal were observed in the Southcentral and Interior regions. Fairbanks (8.0 F/-13.3 C) and McGrath (10.7 F/-11.8 C) both observed their warmest average December temperatures on record. Records in Fairbanks and McGrath began in 1929 and 1941, respectively. Anchorage reported its second warmest December in a 101-year record at an average 25.3 F (-3.7 C). Precipitation was variable across the state, though much of the Southcentral and Southeast regions observed below normal precipitation.
Significant Events for December 2014
December 12: Landslide in Camarillo, California: Following a heavy precipitation event, the hillside above a Camarillo neighborhood gave way and left 13 homes uninhabitable. A brush fire occurred in the region in 2013 and destroyed much of the vegetation that previously anchored the soil. Approximately 9 miles (14 km) away from the landslide, mudslides closed the Pacific Coast Highway and trapped several drivers. Minor flooding and associated damage was also observed elsewhere in the state.
December 30-31: Snow in southern California mountains prompts driver rescues: Heavy snow in the San Bernadino Mountains prompted the rescue of over 100 drivers on the evening of the 30th on Highway 138. Several other mountain highways in the region experienced severe traffic backups due to the storm. In some cases, motorists had to be rescued from their vehicles. Other highways, such as Interstate 15 from Los Angeles to Las Vegas, were closed due to heavy snow.