NOAA's National Centers for Environmental Information
Snowfall at the beginning of March covered approximately 27.6 percent of the contiguous U.S. (CONUS) according to NOAA's National Snow Analysis. Snow blanketed the highest elevations of the Sierra Nevada range, Cascades, Rockies, northern Plains, Great Lakes and from parts of the Appalachians into the Northeast. Throughout the month, snow coverage ebbed and flowed as spring-time troughs brought cold fronts and polar air from Canada, which were followed by ridges of high pressure, ushering in warm air from the Gulf of Mexico. On the 7th, strong northwesterly winds following the passage of a cold front, brought heavy lake effect snows downwind of the lakes, namely from Indiana to New York and across portions of the Appalachian Mountains. Snow cover waxed and waned until a mid-month snow storm brought significant accumulations from Iowa to Pennsylvania, increasing the CONUS snow cover to 32.9 percent — the highest coverage for the month. Snow on the 20th expanded the footprint across Colorado, Nebraska and Iowa and then again on the 26th for South Dakota and parts of Montana. By the end of March, snow covered approximately 12.8 percent of the CONUS, after a period of significant melting. Snow coverage was limited to the northern Great Lakes, northern New England and the higher elevations of the western mountains.
According to NOAA data analyzed by the Rutgers Global Snow Lab, the March snow cover extent was approximately 639,000 square miles, 101,544 square miles below the 1981-2010 average. This was the 18th smallest value in the 54-year satellite record. Above-average snow cover was observed across much of the Northern Tier from Washington to the Great Lakes and into northern New England. Below-average snow cover was present across much of the central and southern Rockies, central Plains, Ohio Valley, and from the Mid-Atlantic into the Northeast.
Melting of winter and spring mountain snowpack is 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 29, SWE values were near- to above-normal across much of the central and northern Rockies and parts of the northern Cascades. Basinwide statistics across the Sierra Nevada range, southern Cascades, the Great Basin and the southern Rockies had SWE values which were as low as 50 percent of the median value for this time of year. By the end of March, SWE values were similar to those from the end of February, although precipitation received during March allowed for SWE values to increase across the Sierras, the Bitteroots, and the central Rockies. SWE conditions worsened across the Painted Desert of Arizona. Much of the West reported SWE values that were at least 75 percent of the median value and were above 100 percent across much of the Rockies.
During the cold season, below-average precipitation and snowfall occurred across the Sierra Nevada mountain range in 2019-2020. It was the 12th driest October-March on record and the 11th driest January-March for California, which is at the heart of the climatological wet season across the West. In addition, temperatures during the first three months of 2020 ranked in the warmest third of California's 126-year record, or approximately 2°F above the 20th century average. It is important for the mountains to capture winter moisture in the form of snow because as temperatures slowly increase in the spring, gradual snowmelt helps keep reservoirs supplied with the water resources needed to make it through the year. The Sierra Nevada range supplies about 75 percent of California's agricultural water and about 60 percent of the water resources for southern California. Despite the dry winter season, reservoir levels across the state remain at normal to above-normal levels, in part due to above-average snowfall during 2018-2019. With the snow season coming to an end, there will be increasing concerns for adequate water resources going into the climatological dry season of summer as well as for enhanced chances of an above-average wildfire season as we approach fall.
Source: NOAA-NOHRSC
Looking at the accumulated contiguous U.S. snowfall for the season-to-date (2019-20) and comparing it with the snowfall received over the previous snow season (2018-19), we can see that the overall blanket of snow in 2019-20 is not as large nor as deep and does not reach as far south as compared with the previous season. Regions where 2019-20 snowfall is lacking include: a large portion of the southern Ohio Valley, Mid-Atlantic and Appalachian regions as well as from from Washington D.C. to Boston. Regions which have received much less snowfall this season compared with the previous season include: The Sierra Nevada range, the coastal ranges, Cascades, the northern and central Plains, the Great Lakes and across parts of northern New England.