NOAA's National Centers for Environmental Information
Approximately 32 percent of the contiguous U.S. (CONUS) was covered by snow at the beginning of January according to NOAA's National Snow Analysis. Snow covered much of the mountainous West, northern Plains, Upper Midwest and parts of the Northeast. This was the minimum extent of snow cover for the month prior to several notable winter storm events. One such event peaked on the 4th with 39 percent snow cover across much of the mountainous West, northern and central Plains, and parts of the Northeast. Snow cover remained steady over the subsequent two weeks and increased to more than 59 percent on the 26th — the maximum snow cover for the month. Snow covered much of the contiguous U.S., from the mountainous West to the central Plains, Great Lakes and Northeast. During the final days of the month, warmer temperatures reduced the snow cover across much of the central Plains, Ohio Valley and parts of the Northeast. By January 31, snow cover was reduced to 48.8 percent coverage.
According to NOAA data analyzed by the Rutgers Global Snow Lab, the January snow cover extent was 1,416,000 square miles, 44,000 square miles above the 1991-2020 average, and the 24th-highest value in the 57-year satellite record. Above-average snow cover was observed across much of the Cascades, Sierras, Great Basin, Rockies, central and northern Plains, western Great Lakes and parts of the Ohio Valley. Below-average snow cover was observed from the southern Plains to the Mid-Atlantic and Northeast and along parts of the West Coast.
Melting of winter and spring mountain snowpack provides a crucial summer 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, which can be approximated by a measure of the snow water equivalent (SWE).
A series of nine atmospheric river events from late December into mid-January dumped a record amount of rain and mountain snow across parts of the western U.S., contributing to the above-normal SWE values across much of the region. On December 31, SWE values were at or above 100 percent of median across most of the western U.S. with portions of the Sierras and Great Basin reporting SWE values in excess of 200 percent of median. By the end of January, SWE values were at or above 100 percent of the median across much of the Sierras, Great Basin, central and southern Rockies and in parts of the Oregon Coast and northern Rockies. Conversely, SWE values across much of the Cascades, Bitteroots and parts of the northern and southern Rockies were near- to below-normal at the end of the month.
