Slippery Roads, December 14, 2024

A combination of freezing rain, sleet, and snow spread across southern and eastern Minnesota on Saturday December 14th, coating roads and surfaces with any icy glaze and leading to dangerous travel conditions with dozens of spin-outs and accidents. A lighter glaze from freezing drizzle within a dense fog affected western and northern Minnesota as well on Saturday night and Sunday.

Cold air had been in place across Minnesota from Thursday into Friday, with subzero (F) low temperatures across the whole state both mornings. Warmer air and moisture began streaming into the region Friday night, in association with weak low pressure to the south. The temperature structure of the air by Saturday morning featured below-freezing conditions at the ground with increasing pockets of above-freezing air between 1000 and 2500 feet above the ground. This warmer air was sufficient to melt some of the falling snow into rain, which then refroze before hitting the ground (sleet) or refroze upon hitting the ground (freezing rain). As a result, an icy mixture of snow, sleet, and freezing rain affected many parts of southern and eastern Minnesota.

The precipitation began as light freezing rain and freezing drizzle, coating roads in rural southern Minnesota with a thin but dangerous sheet of ice by late morning. The light precipitation then moved into the Twin Cities during the early afternoon, accompanied by deteriorating road conditions and rapid increases in spin-outs and crashes. 

Fortunately, pockets of snow and sleet mixed in with some of the freezing rain, leading to a grit-like covering on the ice, which made travel somewhat easier and surfaces somewhat less slippery as the evening wore on. Unfortunately, areas in northern and western Minnesota that had been spared by the main precipitation saw their own glazed surfaces as dense fog with mist in sub-freezing conditions settled into the area.

This was a light precipitation event, with totals of two-tenths of an inch or less. The primary hazard with this system was the ice from freezing rain, which is dangerous in any amount. Farther south in Iowa, the freezing rain was heavy at times and led to a full-fledged ice storm, with damage to trees and power lines reported in central and eastern parts of that state.

Posted December 16, 2024

KAB