NOAA's National Centers for Environmental Information
Approximately 39 percent of the contiguous U.S. (CONUS) was covered by snow at the beginning of March according to NOAA's National Snow Analysis. Snow covered much of the mountainous West, northern Plains and Northeast and portions of the Great Lakes. Snow cover remained steady over the next week before increasing to more than 42 percent — the maximum snow cover extent for the month. Snow cover decreased steadily over the subsequent days before reducing to the minimum extent for the month — 29.0 percent — which occurred on the 21st. During the final days of the month, snow covered much of the mountainous West and northern Plains and in parts of the Great Lakes and Northeast. By March 31, snow covered 29.8 percent of the CONUS. In the West, a parade of atmospheric rivers brought heavy precipitation to parts of the region, resulting in many snowfall records this season.
According to NOAA data analyzed by the Rutgers Global Snow Lab, the March snow cover extent was 1,128,000 square miles, 384,000 square miles above the 1991-2020 average, and the 4th-highest value in the 57-year satellite record. Above-average snow cover was observed across much of the Cascades, Sierras, Great Basin, central and northern Rockies, northern Plains, western Great Lakes and Northeast. Below-average snow cover was observed from the southern Rockies to the Mid-Atlantic.
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 February 28, 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 northern Rockies while much of the Cascades, Bitteroots and parts of the northern and southern Rockies were near- to below-normal. By the end of March, SWE values were at or above 200 percent of the median across much of the Sierras, Great Basin, central and southern Rockies and in parts of Northwest. Conversely, SWE values across the northern parts of the Cascades, Bitteroots and Rockies were near- to below-normal at the end of the month.
