NOAA's National Centers for Environmental Information
Approximately 18 percent of the contiguous U.S. (CONUS) was covered by snow at the beginning of November according to NOAA's National Snow Analysis. Snow cover decreased steadily over the subsequent two and a half weeks to the minimum extent for the month — 2.8 percent — on November 18 before increasing to a coverage of 26 percent on the 27th of the month — the maximum snow cover extent for the month. Snow was present across much of the mountainous West and in parts of the central and southern Plains, Great Lakes and northern parts of the Northeast. During the final days of the month, snow cover reduced to cover across much of the mountainous West and Northeast and parts of the central Plains and Great Lakes. By November 30, snow cover was reduced to 16.7 percent coverage of the CONUS.
According to NOAA data analyzed by the Rutgers Global Snow Lab, the November snow cover extent was 346,300 square miles, 163,000 square miles below the 1991-2020 average, and the 16th-lowest value in the 58-year satellite record. Above-average snow cover was observed from parts of the central Plains to the Great Lakes, in portions of the Northeast and in small parts of the Rockies. Below-average snow cover was observed across much of the West and northern Plains and in parts of central Plains, Mid-Atlantic and Northeast.
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).
On October 31, SWE values were at or above 150 percent of the median across much of the Cascades, Bitteroots, Sierras, Great Basin and in parts of the central Rockies, while much of the Rockies were near- to below-normal during the month. By the end of November, SWE values were below normal across most of the West, while portions of the Oregon Coast and lower Southwest region observed above-normal SWE values at the end of the month.
