After a very active end to the week for the Upper Midwest, the weekend has been a much needed break. However, things change as the new week begins. Another low pressure system rolls off the Rockies and returns the risk for severe storms Monday afternoon and evening. This risk extends from areas like La Crosse, WI to northern Kansas. As this low pressure system moves eastward early this week, warmth and moisture is pumped in from southerly winds. This southerly flow helps to aid in favorable dynamics for severe storms. Behind the cold front associated with this system is much colder air. Where these two contrasting air masses collide is where severe storms will be possible. As the system move east into the Ohio and Tennessee River Valleys on Tuesday, the threat for severe also moves with it.   For WeatherNation, Meteorologist Kate Mantych