Scattered thunderstorms erupted across parts of northern Illinois Monday evening, fueled by an air mass that has become warm and quite humid. Dew points, a measure of atmospheric moisture content, climbed as high as an oppressive 76 degrees at Morris. Higher dew point air not only raises the discomfort level, it also makes the air more unstable. Similar conditions are expected on Tuesday. Storms will likely be ongoing across eastern Iowa and adjacent portions of western Illinois at daybreak. The favorable storm environment is forecast to allow this thunderstorm complex to sweep across a large swath of Illinois and Indiana. Damaging winds and hail are most likely south of the metro area, but some storms may impact areas as far north as Chicago. Partial clearing in the wake of the morning storms will allow the air to again destabilize, bringing a threat of scattered storms late in the day.