Springlike weather to persist through Monday

Satellite imagery late Saturday showed a swirling cloud mass over the upper Midwest. This feature represents a disturbance associated with cold air in the mid and upper levels of the atmosphere. By Sunday afternoon, the core of this cold pool is forecast to lie across the upper Great lakes. Over Chicago, temperatures at an altitude near seven thousand feet are expected to be at or below freezing. This will cause relatively warm, 70-degree air at ground level to ascend into towering cumulus clouds. Scattered afternoon and early evening showers, and a few thunderstorms can be expected both Sunday and Monday. Brief heavy downpours are possible in localized areas. Jet stream flow is forecast to become westerly by midweek, allowing summerlike weather to return.