Mankato (KMKO)-Severe spring storms rolled across southern Minnesota overnight, mainly to the north and east of Mankato.  A flash flood warning was issued for northeastern LeSueur County overnight after heavy rain fell.  That warning was allowed to expire just before 5:00 am.  Meteorologists say there was a slight rise in the Minnesota River level and it could be a concern with more rain expected today through Wednesday.  A hazardous weather outlook for Blue Earth, Brown, Sibley, Nicollet, LeSueur and Waseca counties calls for thunderstorms developing again this afternoon, with severe storms possible mostly in west central Minnesota tonight.