Trajectory forecasts suggest air over portions of South Dakota and Nebraska on Monday, will have moved into the Chicago area Tuesday. This air mass is characterized by seasonably warm temperatures and dry air. Generous sunshine is expected to bring the city its 9th 80-degree day of the season, though mid and high level cloudiness arrives later in the day. Moisture levels are to undergo a modest rise Tuesday night and Wednesday, setting the stage for showers and thunderstorms midweek. Stronger storms are forecast to develop well south of our area, focusing from the mid-Ohio valley to west Texas Wednesday and Wednesday night. By Wednesday evening, a deep upper level trough will send a potent cold front across the area, bringing a push of chilly air with temperatures more typical of early May. This lobe of cool air will be progressive, and temps are expected to be near 80 again on Friday.