As many children and employees took the day off in observance of Dr. Martin Luther King Jr.'s birthday, a dangerous ice storm glazed roads and walkways across the southeastern 1/3 of Minnesota.
The worst conditions covered Albert Lea, Mankato, Rochester, and Red Wing during the day on the 16th, and then expanded northwestward into the Twin Cities area during the evening and overnight period. The storm caused hundreds of spin-outs and accidents, and MnDOT indicated a rate of one incident every 2-3 minutes in the Twin Cities area alone during the height of the storm.
Precipitation amounts in Minnesota between the 16th and 17th ranged from a tenth to nearly a half of an inch, with the vast majority of it coming in the form of freezing rain. Some sleet and snow did fall on top of the ice in in the final hours of the storm, but accumulations were generally kept to less than two inches.
The icy glaze was caused by a shield of liquid precipitation advancing northeastward into an air mass that was near or slightly below freezing at the surface. The system responsible for the precipitation originated in western Mexico, and therefore had very little cold air to help it produce ice crystals, even as it moved into the Upper Midwest. (You can see the storm's circulation crossing Baja on Saturday the 14th.)
The storm had an exceptionally wide reach, with significant and even damaging ice reported from the Texas and Oklahoma panhandles, through Kansas, Nebraska, Iowa, and southern Wisconsin. Fortunately, unlike many ice storms, this one had relatively weak winds, which prevented damage to ice-coated trees and powerlines. In windy conditions, the amounts of ice reported in Minnesota could be expected to cause spotty damage and power outages.
Light glazes have been common throughout the state this winter, but ice accumulations of this sort are somewhat rare in southeastern and east-central Minnesota. Significant ice accumulations appear to be most common along and especially inland from the Lake Superior shoreline, and also in southwestern Minnesota, near the Buffalo Ridge. Indeed, these two areas have seen Minnesota's most recent devastating ice storms, in April of 2013 and March of 2009.