1998 Comfrey–St. Peter tornado outbreak

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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 mile (241 km) as it moved across the southern part of the state during the late afternoon hours. Over $235 million in damage (1998 US$) 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. Seven counties in southern Minnesota were later declared federal disaster areas. The outbreak broke many early season tornado records for the state of Minnesota. The 14 total tornadoes in the state were the most to ever touch down on a single day in March. The F4 tornado was the strongest ever recorded in the state in March, and its 67 mile (108 km) path the longest tornado path ever recorded in Minnesota. In December 1998, the United States Department of Commerce awarded a bronze medal to the Twin Cities office of the National Weather Service (NWS) for providing excellent service to the public during the outbreak event.

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 to push towards Minnesota from the southwest. A low level jet from the south with winds of transported a plume of warm, humid air into the region, helping to push temperatures above and dew points into the middle 60s °F (around 20 °C). By early afternoon, the low pressure area had moved east into Nebraska, while the warm front had moved northward into southern Minnesota. 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 , respectively. All of these factors combined to create very favorable conditions for the development of severe thunderstorms and tornadoes. Shortly thereafter the thunderstorms moved east across the border into Minnesota. After several more reports of severe hail with the growing thunderstorms, the first tornado of the day—rated F2 on the Fujita scale—touched down at 3:23 pm 2 mile (3 km) north of Lismore. It was on the ground for less than 1 mile (2 km) and caused minor damage. Five more tornadoes (all rated F2 or lower) briefly touched down during the next hour in the same general area; none of which inflicted major damage. All of these tornadoes were spawned by the same supercell thunderstorm. During the remainder of the afternoon hours, this supercell would proceed to track east northeast across southern Minnesota for 150 mile (241 km), tracking slightly north of the warm front.

At 3:50 pm a tornado touched down 7 mile (11 km) east of Avoca, Minnesota, in eastern Murray County. As the tornado moved through Cottonwood County, it grew to a width of and obtained F3 strength. It destroyed numerous farms, farm equipment, trees, power lines and poles, vehicles, and other structures in its path. A total of 20 people outside a church near Jeffers were able to get inside the church just before the tornado hit, and as a result nobody suffered serious injuries. At approximately 4:30 pm the twister, which witnesses described as a "mass of blowing dust" or "rolling fog bank" The tornado moved through the center of Comfrey one minute after the sirens went off, and destroyed a grain elevator, the town hall, three of the town's four churches, the grocery store, and most of the main street businesses downtown. The town's firehouse collapsed, and the school was heavily damaged. Of the 200 houses in the town, all but 15 suffered damage. Fifty of those homes were destroyed and as a result 100 people were left homeless. As the tornado continued to move through Brown County it achieved F4 strength and grew to 1.25 mile (2 km) wide. and 500 dairy cattle were lost. In addition to the one fatality,19 people were injured by this tornado.

At 5:18 pm, the same supercell produced another large tornado 2 mile (3 km) to the east of Nicollet. As the tornado moved to the east, a six year old boy was killed when the vehicle his family was riding in was overtaken by the tornado. Gustavus Adolphus College, which sits on top of a hill on the west side of St. Peter, sustained heavy damage after taking a direct hit from the twister. About 80% percent of the windows on the campus were shattered, and most of the major buildings on campus sustained damage. The chapel spire—a campus landmark—was snapped in half. The admissions office was destroyed, as was Johnson Hall, a small dormitory. The Lund Center for Physical Education and Health lost part of its roof, as did the tennis center. The football press box was blown from the top of the stadium bleachers, and the baseball dugouts were damaged. The tornado also uprooted more than 1000 trees, almost completely denuding the campus. The hospital was severely damaged and the library was hit, resulting in a loss of 25% of its books. Officials estimated 500 homes in St. Peter were destroyed, 1700 more were damaged and over 17,000 trees were lost. The half mile (.8 km) wide tornado damaged several farms before hitting Le Center at F2 strength. The tornado damaged many businesses on the southern side of town and caused heavy damage at the Le Sueur County fairgrounds. Over 100 farm buildings were destroyed as well. The last of the 13 tornadoes spawned by this supercell was a brief F0 that touched down 5 mile (8 km) southwest of Hastings, and the supercell dissipated a few minutes later as it moved into Wisconsin.

On April 1, 1998, seven counties in Minnesota were declared federal disaster areas: Brown, Le Sueur, Nicollet, Rice, Cottonwood, Blue Earth and Nobles. The money allotted from the federal government allowed the affected towns to clean up the damage and begin the rebuilding process. In addition to the federal dollars, the state of Minnesota contributed $27.6 million to the cleanup and rebuilding effort, with $1.35 million designated specifically for the preservation of the historical buildings in St. Peter. Most of St. Peter's buildings that were on the National Historic Register were damaged, but only one—a French Second Empire school building built in 1871 (St. Peter Central School)—had to be demolished. Three years after the tornado, the City of St. Peter reported that its population had grown by 2%; an unusual feat for a town that had so recently endured a natural disaster. Damage to the Gustavus campus was estimated at nearly $60 million. Following the storm, a major concern for the college was that the student base would be eroded. To prevent that from happening, every returning and graduating student was given a $3,000 check by the college. In addition, the school sent out letters and made phone calls to all 2,000 applicants within 10 days of the disaster. The 735 new students who reported to Gustavus the following fall comprised the largest incoming class in the school's history. Following the tornado in Comfrey, residents were forced to temporarily evacuate the town due to several gas leaks, To help stock their classrooms, the school used equipment and supplies that had been salvaged from the damage as well as items that had been donated. Immediately following the tornado in Comfrey there was uncertainty about the town's long term survival. Then in the week following the tornado the town decided to rebuild the school, and as a result most of Comfrey's businesses decided to follow suit. Ground was broken on the new school early the next year, and it opened to students on October 4, 1999. The population of Comfrey is down to 367 from the 425 it was when the tornado hit. Official U. S. government totals gathered in the months following the disaster state that the tornadoes caused $235 million in damage, however later estimates put the total much higher, including over $300 million in St. Peter alone.

Tornadoes during the month of March are an unusual occurrence in Minnesota when compared to the rest of the spring and summer months. Before this event there had been only six tornadoes ever recorded in the state during March, and since this event there has been only six. This outbreak also marks the first time in Minnesota history that two tornadoes were recorded on the same day in March, Despite the historical significance of the outbreak, this was not the earliest calendar year tornado to touch down in Minnesota; that record is held by three tornadoes that touched on March 6, 2017. It is however the longest continuous track tornado in Minnesota history, meaning that it was the longest to have been observed to always be in contact with the ground. The damage from the F4 tornado that struck Comfrey is the strongest ever measured in Minnesota during the month of March. The previous strongest measured were two F3's, occurring on March 27, 1905, and March 26, 1921.