Frost cover means spring's warmth could lead moisture to run off into lakes and rivers rather than seep into the ground.
Recent blasts of "wintry mix" across southern Minnesota and a foot or more of snow expected across much of western Minnesota over the weekend could turn the state's late winter and spring into something of a paradox:
"We could have a flood on top of a drought," said assistant Minnesota state climatologist Pete Boulay.
Soils are extremely dry over most of the state, and a cap of frost could well prevent most of the moisture in the snow and ice now lying on the landscape from soaking into the ground when spring warmth arrives. In that case, it would run off into lakes, streams and rivers.
Across much of Minnesota, nearly 4 inches of precipitation is being held in snow and ice on top of the ground, making the prospect of minor flooding "more realistic," said Greg Gust, hydrologist with the National Weather Service office in Grand Forks, N.D. In western Minnesota, where the city of Rothsay received 21 inches of snow Sunday and Monday, that new snow alone holds about 2 inches of water.
Across the Twin Cities metro area, the water content of the snow and ice is 2 to 3 inches and illustrates something of a turnaround. After a dry late summer and fall -- much of the metro area has been in "severe" drought since fall -- precipitation has been running well above normal since Dec. 1. Some fell as rain in December, and again on Sunday, but seasonal snowfall for the Twin Cities is now 80 percent of normal. Sunday's snowfall was only 2.2 inches in the metro area, but it held 0.62 inch of water -- a precipitation record for the date and the second such record in the past two weeks.
Diane Cooper, hydrologist with the North Central River Forecast Center in Chanhassen, said the region will need a gradual warmup, featuring warm days and subfreezing nights, for that water to get into the ground below. Alleviating drought conditions going into the growing season would require significant snow followed by a gradual warmup.
"I wouldn't wish that much snow on anybody right now," she said.
Weekend winter wonderland
Last weekend's snow-rain-sleet attack was in keeping with an odd recent pattern of Twin Cities weather. Since November 2010, just before the storm that collapsed the Metrodome roof, 65 percent of the snow that has fallen on the Twin Cities has come on Fridays, Saturdays and Sundays. In other words, snowstorms have been a decidedly weekend phenomenon for three winters.
Minneapolis street maintenance superintendent Mike Kennedy said he's well aware of that.
"Our folks notice when they have to work on weekends," he said.
Weekend storms might make plowing easier without rush hours, but they reduce compliance with snow emergencies because residents are out of their regular routines, Kennedy said. And they cost the city extra money in overtime pay, he added.
Tom Knisley, spokesman for Three Rivers Park District, said storms reduce attendance at winter parks, though skiers, snowboarders and tubers tend to turn out in even greater numbers in the days after the snow stops.
Bill McAuliffe • 612-673-7646