page_title: 1998 Comfrey–St. Peter tornado outbreak
section_title: Meteorological synopsis
hierarchical_section_title: 1998 Comfrey–St. Peter tornado outbreak / Meteorological synopsis
caption_attribution_description: Surface map from March 29, 1998
context_page_description: 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 as it moved across the southern part of the state during the late-afternoon hours.
  Over $235 million in damage was recorded from the tornadoes, two people were killed, and 21 others were injured. Most of the damage was caused by three tornadoes—one rated F4 on the Fujita scale that hit the town of Comfrey, Minnesota, an F3 that hit St. Peter, Minnesota, and an F2 that hit Le Center, Minnesota. Gustavus Adolphus College in St. Peter was especially hard-hit, with several buildings damaged or destroyed, 2,000 trees lost, and nearly 80% of the windows on the campus shattered. In Comfrey, 75% of the structures in the town were damaged or destroyed, including the local K–12 school.
context_section_description: The driving force behind this tornado outbreak was a strong surface-based low-pressure area stationed over the western high plains. On the morning of March 29, the low was centered over eastern Wyoming, with a warm front stretching eastward across Nebraska and Iowa. An upper-level trough of low pressure was centered over the southwestern United States, which caused an upper-level jet stream with winds of 100 knots (120 mph; 190 km/h) to push towards Minnesota from the southwest. A low-level jet from the south with winds of 50 knots (60 mph; 90 km/h) transported a plume of warm, humid air into the region, helping to push temperatures above 70 °F (21 °C) and dew points into the middle 60s °F (around 20 °C). Winds on the surface were from the southeast, which created low-level wind shear; enhancing the potential for tornadoes.
  By early afternoon, the low-pressure area had moved east into California, while the warm front had moved northward into southern Minnesota. The atmosphere to the south of the warm front was strongly capped, meaning that the best chance of thunderstorm development was in areas along and slightly north of the front. By the time the thunderstorms started developing, CAPE values were 2000 J/kg, indicating moderate atmospheric instability. Also present were low-level and deep-layer wind shear values of 44 and 87 knots (51 and 100 mph; 81 and 161 km/h), respectively. All of these factors combined to create very favorable conditions for the development of severe thunderstorms and tornadoes.
caption: Surface map of the upper Midwest on March 29, 1998, at 3:00 pm CST (2100 UTC)
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