As Indiana battles the highest floodwaters in a century in the south and recovers from ice-storm related power-outages in the central and north, the first part of the week Chicagoans will see temperatures for the most part above freezing with highs in the upper 30s to lower 40s. Wednesday should see warming well into the 40s maybe even hitting 50°.
These seasonably mild readings (averaging some 15° above normal) combined with gusty winds and a good chance of rain Tuesday and Wednesday will melt/evaporate much of the snow that presently covers northeast Illinois. However a major shift in jet stream flow mid-week will open the doors to a northerly flow that will tap Arctic cold and shunt the coldest air of the winter into the Midwest the latter half of the week. The coldest air will hit Friday and Saturday with single-digit daytime highs and sub-zero overnight lows.
