The National Weather Service says thunderstorm activity will become more widespread across eastern South Dakota and west central Minnesota later this afternoon.
Some of the thunderstorms could become severe with the main threat being large hail and damaging winds. An isolated tornado may also be possible for locations in extreme northeast South Dakota and west central Minnesota.
Much of northeast South Dakota, eastern North Dakota and the Red River Valley region of Minnesota remains under a tornado watch until 10 p.m. tonight.
Update 9 a.m.
The National Weather Service says there is a slight risk for severe thunderstorms late this afternoon and tonight from most of central and southern Minnesota. The NWS also said it's likely that super cell thunderstorms will develop this afternoon over northwest Minnesota
The greatest risk for severe weather will exist from west central Minnesota into parts of central Minnesota through tonight. Conditions in this threat include very large hail, damaging winds and isolated tornadoes.
West central Minnesota counties included in this watch area are Douglas, Todd, Stevens, Pope, Stearns, Lac qui Parle, Swift, Chippewa, Kandiyohi, Meeker, Wright, Yellow Medicine, Renville, McLeod and Redwood.
An unusually strong upper level low is expected to intensify in southern Saskatchewan by early this morning before moving toward the international border. The complex system will track east across the Dakotas during the day and enter northern Minnesota tonight.
"We just don't get them as strong this time of year," said NWS meteorologist Peter Rogers. "Normally, these strong upper level lows occur in winter time. The jet stream is also very strong, and with that upper level instability, the potential for a line of storms to develop is very real; where and when is not certain."
Ahead of the front, strong southerly winds near the surface will draw significant moisture from the Gulf of Mexico. "The strong directional turning of winds in the lower portion of the atmosphere will allow rotating super cell thunderstorms to develop with the potential to form tornadoes," Rogers said.
Thunderstorms are expected to develop this afternoon across eastern North Dakota and northeast South Dakota. This activity will move easy and approach west central Minnesota by late afternoon. By this evening, the storms are expected to develop into a line that will track across northern and central Minnesota and last through Tuesday night and into Wednesday.
As a strong cold front enters Minnesota Wednesday will result in a slight chance of severe thunderstorms continuing into Wednesday evening for parts of central Minnesota.