The high temperature of 12, and low of -3 recorded at O’Hare International Airport on Monday yielded an average of just 5 degrees, a reading 29 degrees below normal. Making these frigid temperatures even more remarkable for this late in the season, is that they were observed with no snow cover. Typically, our early March sunshine incident on bare ground is strong enough to effectively modify intrusions of polar air. Over snow covered areas of northwest Illinois and Wisconsin, daytime temperatures struggled to reach the mid and upper single digits. The core of most intense cold will begin to shift east of the Great lakes on Tuesday, allowing temperatures to moderate slightly. Slow warming is expected through Friday, but readings are still forecast to average about 14 degrees below normal. Deepening low pressure over the Plains on Saturday promises to bring a more substantial spike in temperature.