Polar jet stream over Chicago area map depicts 30,000-foot jet stream flow aloft and low-level/surface temp distribution

With “Split-flow” aloft, Saturday the polar jet stream reaches down just south of the Great Lakes, allowing the southern edge of Arctic-source cold air to ease into the Chicago area. Later this weekend into next week, the southern Subtropical Jet Stream will become more prominent here, as the Polar Jet recedes back north to the U.S./Canadian border. This will allow more “seasonable” temps back into our area – the “normal” high/low temps here the first week of December run in the upper 30s to around 40 for a high and upper 20s for low temps.