NOAA's National Centers for Environmental Information
This is the time of year when the steadily rising sun angle results in climatologically warming temperatures and a seasonally contracting snow cover. April 2019 began with about 21 percent of the CONUS covered in snow, mostly in the high western mountains and along the Canadian border from Minnesota to New England. With a couple of exceptions, the snow coverage followed the seasonal script and steadily declined throughout the month. The first exception occurred near mid-month when a powerful low pressure system crossed the center of the country, pulling in Gulf of Mexico moisture from the south and below-freezing Canadian air from the north to create an extensive blanket of deep snow from the central Plains to western Great Lakes. According to NOAA's National Snow Analysis, snow coverage peaked on April 12th at 26.6 percent of the CONUS, then rapidly declined in the following days as the low moved out into Canada, to bottom out at about 5 percent on the 27th. The second exception occurred at the end of the month when a low pressure system tracked along the Canadian border and dropped a snow cover from northern Montana to northern Minnesota, raising the CONUS snow cover area to 12.1 percent on the 30th.
According to NOAA data analyzed by the Rutgers Global Snow Lab, the April snow cover extent was nearly 303,000 square miles, 21,000 square miles above the 1981-2010 average. This was the 22nd highest value in the 53-year satellite record. Above-average snow cover was observed across the northern Plains, Great Lakes and into New England, below-average snow cover across the central High Plains and parts of the West.
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 31st, SWE values in excess of 200% of median were observed across the Sierra Nevada range, the Great Basin and across much of northern Arizona. Near-to and above-median SWE values were present across much of the southern Cascades and Bitterroots as well as the central and southern Rockies. Below-average SWE values intensified across the northern Cascades as well as the northern Bitterroots. By the end of April, SWE values in excess of 200% of median were again observed across the Sierra Nevada range and across parts of the Great Basin and northern Arizona. Near-to and above-median SWE values were present across much of the southern Cascades and Bitterroots as well as across much of the Rocky Mountain range. Below-average SWE values persisted across the northern Cascades.
A significant snow event occurred across the northern Plains from April 9-12, bringing blizzard conditions and large amounts of snow to the region. Watertown, SD, reported 25 inches of snow during this event, which is Watertown's largest single-storm snowfall on record and the largest three-day total on record. For the season, Watertown accumulated 81.9 inches of snow, which eclipsed the previous record of 79.4 inches set back in 2010-2011. Mitchell, SD, reported 16.2 inches and Huron, SD, accumulated 18 inches. According to the Regional Snowfall Index (RSI) for the Northern Rockies and Plains region, this storm ranked as a Category 3, which is the highest rank for a snow event in this region since October 2013.
April 15, 2019 Visible Satellite of Great Lakes snow cover
Source: NOAA
This April 15th GOES East visible satellite view of the Great Lakes shows a swath of fresh snowcover from western Illinois to Lake Huron. Chicago received 5.3 inches of snow on the 14th — the second snowiest calendar day on record this late in the snow season. The record is 5.4 inches, which occurred on April 16, 1961. Other impressive snow totals hailed from Sylvester, MI (9.1 inches), Union Grove, WI (9.0 inches), and Big Rapids, MI (9.0 inches). More than 1,000 flights were cancelled in the Chicago area as a result.
2018-2019 Seasonal Snowfall Totals Source: NOAA
As the 2018-2019 snow season comes to an end, it is important to note that it was a very active season across northern Maine, the northern Great Lakes, northern Plains, as well as the higher elevations of the Rocky Mountains, the Sierra Nevada range, and the Cascades. Looking at the seasonal snowfall analysis on the left, a significant fraction of the county received four or more feet of snow over the course of the season, with some totals in the higher elevations exceeding 40 feet. The Sierra Nevada range in California had its fourth snowiest season with an average of 60.6 inches of liquid equivalent near the end of April. Some ski resorts in this region reported seasonal accumulations in excess of 600 inches. By and large, it was a near-average season for much of the rest of the Contiguous U.S.