NOAA's National Centers for Environmental Information
It was a slow start to the beginning of the 2021-22 snow season with less than one percent of snow cover across the contiguous U.S. (CONUS) until October 10. During mid-October, a potent cold front swept across the western U.S. and brought cold Canadian air and snow to portions of the Cascades, Bitterroots, Great Basin and central and northern Rockies. According to NOAA's National Snow Analysis, snow cover peaked for the month at about 12.4 percent on October 13 prior to melting following a rebound in temperatures that typically occurs after a cold spell during October. A smaller snow event from October 24-27 brought snow to the higher elevations of the Sierras and central Rockies. This snow resulted from a series of atmospheric river events that yielded record rainfall in portions of the drought-stricken West, helping to quench active wildfires and lessen the drought severity. By the end of the month, only 2.2 percent of the CONUS was covered by snow.
According to NOAA data analyzed by the Rutgers Global Snow Lab, the October snow cover extent was about 32,400 square miles, 47,000 square miles, below the 1991-2020 average. This was the 23rd lowest value in the 54-year satellite record. Above-average snow cover was observed across pockets of the Sierras and central Plains. Below-average snow cover was observed across much of the northern and central Rockies into the northern Plains.
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). At the end of October, with October marking the beginning of the snow season across the Lower 48, SWE values in excess of 150% of median were observed across portions of the northern Cascades, Bitterroots, Sierras, Great Basin and central Rockies. Below-average SWE values existed across portions of the northern Rockies, southern Cascades and southern Rockies. It is important to note that since it is early in the snow season, normal median values are typically low, which can result in ususally high percent of median values when snow does fall.