K-State Research and Extension News
January 15, 2009
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Weather Wonders: Glare Ice a Wintry Road Hazard


MANHATTAN, Kan. – “Glare ice” is a winter weather term that many don’t know about, although they may have observed it, said State of Kansas Climatologist Mary Knapp.

“Unlike black ice, which is nearly invisible, glare ice a highly reflective ice surface -- whether on sea, land or glacier. Kansans typically notice it first on road surfaces, where it can be quite a hazard,” said Knapp, who heads the Kansas Weather Data Library, based with Kansas State University Research and Extension.

In general, glare ice falls into three broad categories, she said. The first and most common results from the compaction of previous storms’ snow, ice or slush.

“Most Kansas drivers are familiar with this type, having seen at some time a light, powdery snow compacted into a treacherous slab of ice,” Knapp said.

A less common category is the film of ice produced when car exhaust condenses on a roadway. It’s most likely to be a problem where cars sit and idle for a while, such as at yield signs and stoplights.

The third category of glare ice appears when water condenses or ice crystallizes directly from the air onto a road surface. For that to occur, the road surface must be colder than the air above it. The process is most likely when the air is fairly humid and temperatures are edging upward after a long, ground-freezing cold spell. 

“This form of glare ice is most usual in the northern areas of the country. It’s also the category that most resembles black ice,” Knapp said.

More information about Kansas weather is available on the Kansas Weather Data Library Web site: http://www.oznet.ksu.edu/wdl. Audio reports of “Weather Wonders” are available on the Kansas Radio Network http://www.oznet.ksu.edu/radio/ (click on Weather Wonders and scroll). 



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K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.

Story by: Mary Lou Peter
mlpeter@ksu.edu
K-State Research & Extension News

Mary Knapp is at 785-532-7019.