December in the West
Dry and generally cool conditions were observed in much of the West this month as high pressure dominated the region. Several systems made their way across the Southwest, bringing above normal precipitation to the area. Montana experienced a very warm month. Many locations in the West experienced damaging high winds this month associated with passing cold fronts or Santa Ana conditions.
December temperatures were below normal in much of the West with the notable exception of the upper Missouri River Basin. During the second half of the month, many locations in Montana saw positive temperature departures from normal in the double digits. Glasgow, Montana airport experienced its 11th warmest December monthly average at 23.8 F (-4.5 C) in a record beginning in 1955. A number of locations in New Mexico and southern Colorado experienced cold conditions, many 6-10 F (3-6 C) below normal. Roswell, New Mexico averaged 34.5 F (1.38 C), the 8th coolest in a record dating from 1894. With clear skies in western portions of the region, daytime highs were well above average, and nighttime lows were well below average.
Precipitation was below normal in much of the West this month. A series of storms passed through the Pacific Northwest during the last week of the month, staving off near-record dryness, but still only about half the average. A series of cutoff low-pressure systems moved across the Southwest during the first half of the month, bringing above normal precipitation to Arizona, New Mexico, and Southern Colorado. Pueblo, Colorado airport recorded its 5th wettest December with 0.84 in (21.3 mm) on a record beginning in 1954. Albuquerque, New Mexico recorded their 9th wettest December with 1.2 in (30.5 mm).
Many locations in California and Nevada experienced record or near-record dry conditions. Reno, Nevada reported its lowest December total (not even a trace) in 129 years (1883 and four prior years also had no precipitation). Fresno, California reported no measurable precipitation for the 2nd time since 1878 (tied with 1989). Downtown San Francisco received 0.14 in (3.6 mm), the 3rd driest December since 1849, behind only the 0.00 readings of 1876 and 1989. San Jose (2nd driest since 1874) and Sacramento (6th driest since 1849) also had a notably dry month, and an index of 8 Sierra Nevada stations recorded its second lowest December total since 1920, and 4th lowest July-December.
Significant Events for December 2011
December 1-2: Santa Ana Wind Event: A strong wind event affected much of the Southwest. Gusts of 140 mph (225 kph) were recorded at the crest of the southern Sierra Nevada. Gusts to 80 mph (128 kph) were recorded in the Los Angeles area. Many power lines and trees were downed in Southern California, and on the 1st, 200,000 people were without power in the Los Angeles area. Pasadena, California declared a state of emergency following the wind event. Several wildfires broke out with the dry, warm air created near the coast. Albuquerque, New Mexico, Las Vegas, Nevada and Salt Lake City, Utah were also affected by this wind event and recorded high gusts.
December 3-5: Snowstorms in West: The low pressure system that helped to generate high winds over the Southwest moved northeast, bringing snowfall to the southern Rockies and plains. Most basins in northern Arizona and New Mexico and Colorado received 4-8 in (10-20 cm). Higher altitude locations like Taos, New Mexico received up to 18 in (45.7 cm) of snowfall.
December 11-12: Southwest Precipitation Event: Another cutoff low moved down the West Coast and then inland on December 11-12, bringing significant precipitation and snowfall to Southern California, eastern Nevada, southern Utah, and northern Arizona and New Mexico. Several inches of snow were received throughout the area, with highest storm totals of up to 8 in (20 cm) along the Arizona/New Mexico border. San Diego received a storm total of 0.67 in (17 mm), one-third of the location’s average December total of 1.78 in (45.2 mm).
December 19th: New Mexico/Southeast Colorado Snowstorm: New Mexico and Southeast Colorado received several inches of snow with totals up to 1 foot (30.4 cm) at high elevations. High winds and low visibility associated with the storm caused road closures and travel difficulties on several major travel routes.
December 30-31: Colorado/Wyoming High Wind Event: Damaging wind gusts up to 75 mph (120 kph) occurred in southern Wyoming and northern Colorado. High profile vehicles and tractor-trailers were knocked over on some Wyoming highways. A roof was torn of a warehouse in Cheyenne, Wyoming injuring two people, and a falling tree branch killed a man in Boulder, Colorado. Localized power outages were also experienced throughout the region.