NOAA's National Centers for Environmental Information
During December, record warmth engulfed the eastern half of the contiguous U.S. while parts of the West had near-average temperatures. Most of the country had above-average December precipitation, particularly the Northwest, Great Plains, Midwest, and Southeast. Where it was warmer than average, the precipitation fell as rain and below-average snow cover was observed. Where temperatures were near-average, some of the precipitation fell as snow, contributing to above-average snow cover extent. According to NOAA's National Snow Analysis, on December 1st, 38.7 percent of the contiguous U.S. was snow covered — the Sierra Nevada and Cascade mountains, northern parts of the Great Basin, and parts of the Northern Rockies and Plains. By the end of the month, 54.0 percent of the contiguous U.S. had snow on the ground — much of the high terrain in the West, most of the Great Plains, Upper Midwest, and northern parts of New England.
According to NOAA data analyzed by the Rutgers Global Snow Lab, the monthly snow cover across the contiguous U.S. was 1.20 million square miles, 16,000 square miles above the 1981-2010 average. This ranked as the 22nd largest December snow cover extent in the 50-year satellite record. During the month, above-average snow cover was observed across much of the West, Rocky Mountains, and Great Plains. Below-average snow cover was observed across the Midwest and the Northeast.
Winter and spring mountain snowpack provide a crucial water source across much of the western United States. The total annual water budget for agriculture and human use in the mountainous West is highly dependent on the amount of snow melt that will occur in spring and is proportional to the amount of snow on the ground. On January 1st, below-average snowpack was observed in parts of the Northern Rockies and southern Alaska. However, above-average precipitation across most of the West during December boosted snowpacks, particularly in the Sierra Nevada Mountains, Cascade Mountains, and the Central and Southern Rockies. Several winter storms impacted this region during the month, bringing beneficial precipitation. The area is dealing with significant drought conditions that started earlier this year in the Northwest and have been present in California for over five years. The storms were also cold in nature, in contrast to the past several years, allowing snow levels to drop and contributing to above average snowpacks across the region. Although the region has a long way to go in terms of making up long-term precipitation deficits and drought recovery, the 2015/16 winter season is off to a good start.