...There is a slight risk of severe thunderstorms over parts of the Upper Midwest...
...Heavy rain possible over parts of the Upper Mississippi Valley...
A quasi-stationary front will extend from the Upper Great Lakes to the
Central Plains/Central Rockies. A wave of low pressure over the Central Plains will lift northward into western Ontario by Sunday evening. Showers and thunderstorms will develop along and near the boundary from the Northern/Central Plains to parts of the Northeast through Sunday.
Meanwhile, an upper-level low over the Southeast will slowly lift
northward into the Ohio Valley. The energy will aid in producing showers and thunderstorms along parts of the Central/Eastern Gulf Coast and the Southeast Coast, also through Sunday.
In addition, upper-level energy over the Northern Rockies will move to
Northern Plains by Sunday. The energy will produce showers and
thunderstorms over parts of the Northern Rockies/Northern High Plains into parts of the Northern Plains by Sunday morning.
Furthermore, a front will approach the Pacific Northwest on Sunday
bringing rain to the Pacific Northwest/Northern California.