Spring Snow in Northern Illinois
May 05, 2009
On the morning of March 29th a fast-moving snowstorm hit northeastern Illinois, dumping 4 inches (10 cm) of wet snow. This snow, because of its high water content, was heavy enough to break 6 inch (15 cm) diameter branches on a few deciduous trees in our suburb of Chicago. Notice the patch of green grass in the middle of the yard. Despite the snow cover, the ground was still relatively warm and conducted heat into the new fallen snow. Where the veneer of snow was thinner, it quickly melted. While snow is a very good insulator, it’s a poor conductor. The air temperature just above the snow surface was still very close to the temperature of the snow itself, about 32 F (0 C).
Just a few days prior to this storm, the temperatures were in the 60s F (15-20 C). Weather records have revealed that snow can accumulate through April in the Chicago area and snow has fallen as late as May 11th. As some Scots are fond of saying "Dunna toss your coat til May is out." Good advice for Scotland and for northeastern Illinois as well. Also, don’t make the mistake of putting away your snow shovels and snow blowers too soon.