High Quality Content by WIKIPEDIA articles! The 1998 Comfrey – St. Peter tornado outbreak was an unseasonably-strong tornado outbreak which affected the Upper Midwest region of the United States on March 29, 1998. A strong area of low pressure combined with a warm front and favorable upper-level dynamics to produce 16 tornadoes across the region—14 in Minnesota and two in Wisconsin. Thirteen of the tornadoes in Minnesota were spawned by a single supercell thunderstorm. This supercell remained intact for approximately 150 miles (240 km) as it moved across the southern part of the state during the late-afternoon hours.