National Snow & Ice - April 2018
During April, below-average temperatures spanned the contiguous U.S. from the Rockies to the East Coast with record cold in parts of the Midwest. The Southwest was warmer than average. Below-average precipitation was observed in the Southwest, much of the Great Plains and parts of the Midwest. Above-average precipitation was observed along both coasts with much-above-average precipitation in the Northwest. Winter storms across the north-central U.S. kept snow on the ground during much of the month, with several locations in the upper Midwest having record April snowfall. According to NOAA's National Snow Analysis, on April 1st, 19.6 percent of the contiguous U.S. had snow on the ground — the high elevations in the West, the central High Plains, Northern Plains, Upper Midwest, and parts of the Northeast. The monthly snow cover peaked on April 7th, with 32.2 percent of the Lower 48 having snow on the ground. By the end of April, 5.4 percent of the contiguous U.S. had snow on the ground — the highest elevations in the West, parts of the western Great Lakes, and parts of the Northeast.
U.S. April Snow Cover Extent Anomalies
Source: Rutgers Global Snow Lab
According to NOAA data analyzed by the Rutgers Global Snow Lab, the monthly snow cover across the contiguous U.S. was 508,000 million square miles, 227,000 square miles above the 1981-2010 average and ranked as the fifth highest value in the 52-year period of record. This was the highest April snow cover extent since 1997. Above-average snow cover was observed across parts of the Northern Rockies and Plains, Upper Midwest, and the Northeast. Below-average snow cover was observed in the Southwest and Central Rockies.
May 1 Mountain Snowpack
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. On April 1st, above-average snow pack was observed across the northern Cascades and the northern Rockies with snow totals more than 150 percent of average for many locations. Below-average snowpack was observed in the southern Cascades, Sierra Nevada Mountains, Great Basin, and southern Rockies. Some locations in these regions had snowpack totals less than 25 percent of average. Below-average snowpack was observed in southern Alaska with above-average conditions across interior parts of the state.
April brought historic snowfall to parts of the Upper Midwest. A potent storm system hit the region between April 12th and 16th, dropping heavy snowfall in Minnesota, South Dakota, Iowa, Michigan, and Wisconsin. Green Bay, Wisconsin received 24.2" of snow during the event, the heaviest April snow storm total ever observed in the city, surpassing the previous record of 11.0" in April 1977. This was also the second heaviest snowfall of any storm for any month. The record heaviest snow storm for Green Bay was 29.0" and occurred in March 1888. For the entire month, the city received 36.7" of snow, the most April snowfall on record, more than doubling the previous April record of 15.1" set in 1907, 111 years ago. Other nearby cities, including Appleton, Wausau and Rhinelander also observed their snowiest or second snowiest April on record. According to the Regional Snow Index (RSI), which takes into account snowfall on population to understand societal impacts, the mid-April storm was a Category 4 or 'crippling' event for the Upper Midwest. This was also the fifth highest RSI score for the region, highest for the month of April, and highest for any month since November 1991.