Approximately 30 percent of the contiguous U.S. (CONUS) was covered by snow at the beginning of April according to NOAA's National Snow Analysis. Snow covered much of the mountainous West, northern Plains and parts of the Great Lakes and Northeast. Snow cover remained steady for a few days before increasing to nearly 31 percent on the 5th — the maximum snow cover extent for the month. Snow covered much of the mountainous West, northern Plains and parts of the central Plains, Great Lakes and Northeast. Snow cover decreased steadily over the subsequent weeks, during the final days of the month, snow covered parts of the mountainous West and Great Lakes. By April 30, snow covered only 6.9 percent of the CONUS.
According to NOAA data analyzed by the Rutgers Global Snow Lab, the April snow cover extent was 482,000 square miles, 203,000 square miles above the 1991-2020 average, and the 7th-highest value in the 57-year satellite record. Above-average snow cover was observed across much of the Sierras, Great Basin, central and northern Rockies, western Great Lakes and in parts of the Cascades and northern Plains. Below-average snow cover was observed across parts of the southern Rockies, Plains 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 March 31, 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, while the northern parts of the Cascades, Bitteroots and Rockies were near- to below-normal. By the end of April, SWE values were at or above 200 percent of the median across much of the Sierras, Great Basin, central 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.