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 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 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.
Meteorological synopsis
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). 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 Nebraska, 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 , respectively. All of these factors combined to create very favorable conditions for the development of severe thunderstorms and tornadoes.
The thunderstorms that would eventually spawn the tornadoes began forming in southeastern South Dakota around 2:00 pm. The first severe weather report of the outbreak was of diameter hail south of Brandon, South Dakota. 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 north of Lismore. It was on the ground for less than 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 , tracking slightly north of the warm front.
Forecasts
Weather forecasters first began to notice the severity of the impending weather situation after the 6:00 pm CST (0000 UTC) computer model runs on the night of Friday, March 27. On Saturday, March 28 at 11:30 am the Storm Prediction Center issued a Day 2 moderate risk of severe weather for southeast Minnesota, northeast Iowa, northwest Illinois and much of Wisconsin. Later model runs on March 28 only increased forecasters' confidence that a major severe-weather event would occur the following day.
In the early-morning hours of Sunday March 29, forecasters at the Twin Cities NWS noticed that due to the model's prediction of strong wind shear and instability, the tornado risk was quite high for their region. Area forecast discussions during this period mentioned the possibility of F3-strength tornadoes later in the day. Also on the morning of March 29, the Storm Prediction Center issued a Day 1 moderate risk of severe weather. This moderate risk area was more narrow than the previous day's outlook, encompassing only southwest Wisconsin, northern Iowa and the southern third of Minnesota.
As the day moved on, the Twin Cities, Sioux Falls and La Crosse NWS forecast offices all saw the potential for "strong to violent" tornadoes, and used such verbiage in their forecasts. The Twin Cities NWS noted in their 12:26 pm forecast discussion that "thunderstorms located south of a Redwood Falls to Minneapolis to Rice Lake line could be particularly strong with the potential of tornadic thunderstorms". Just before 12:00 pm, the Storm Prediction Center issued a mesoscale discussion stating that "[g]iven strength of vertical shear profiles, CAPE on the order of 2000 J/kg will support increasing potential for tornadic supercells during the afternoon hours, especially along an axis roughly from Yankton through Sioux Falls into Redwood Falls and Minneapolis/Rochester areas. We will continue to monitor. Present indications are WW (Weather Watch) will be necessary within the next 2 to 3 hours." At 1:35 pm the Storm Prediction Center issued tornado watch No. 132 with a particularly dangerous situation designation. The watch area encompassed most of southern Minnesota and northern Iowa, along with small parts of northeast Nebraska, southeast South Dakota, southwest Wisconsin, and was made in effect from 2:00 pm to 8:00 pm.
Confirmed tornadoes
March 29 event List of confirmed tornadoes – Sunday, March 29, 1998F# Location County Time (UTC) Path length DamageMinnesotaF2N of LismoreNobles21230 miTornado destroyed buildings, and damaged trees along with numerous pieces of farm equipment. Two cattle were killed.F0E of LeotaNobles2125 pm0 miTornado damaged trees and a few buildings.F0N of WilmontNobles2128 pm0 miTornado damaged trees and a few buildings.F2NW of St. KilianNobles2135 pm0 miTornado destroyed farm buildings, uprooted numerous trees, and flipped a tractor-trailer.F1NE of St. KilianNobles2145 pm0 miTornado damaged trees and destroyed some old farm buildings.F4E of Avoca to E of CourtlandMurray, Cottonwood, Brown, Watonwan, Blue Earth, Nicollet2150 pm67 mi (108 km)1 death – See section on this tornadoF1SW of FuldaMurray2155 pm0 miTornado damaged trees and destroyed some old farm buildings.F0W of WabashaWabasha2307 pm2 mi (3 km)Brief tornado caused no damage.F3E of Nicollet to W of Le CenterNicollet, Le Sueur2318 pm18 mi (29 km)1 death – See section on this tornadoF2Le CenterLe Sueur2348 pm17 mi (27 km)See section on this tornadoF1SW of LonsdaleRice0009 pm0 miDetails unknown.F2LonsdaleRice0016 pm5 mi (8 km)Considerable damage in the area. Four homes and 6 businesses were severely damaged. The street department building was damaged, and 20 farms were damaged or destroyed.F2WNW of Castle RockDakota0025 pm3 mi (5 km)Details unknown.F0SW of HastingsDakota0043 pm1 mi (1.6 km)Brief tornado caused no damage.WisconsinF0S of MaxvilleBuffalo2315 pm1 mi (1.6 km)Brief tornado caused no damage.F0NW of TomahawkLincoln0128 pm1 mi (1.6 km)Tornado damaged several sheds, garages and a pole building.Source: National Climatic Data Center
Comfrey, Minnesota
At 3:50 pm a tornado touched down 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" entered Comfrey, a town of 550 people located in both Cottonwood and Brown Counties. Comfrey's fire chief saw the tornado while storm spotting and ordered the town's sirens activated. 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. Approximately 75% of the buildings in Comfrey were damaged or destroyed.
As the tornado continued to move through Brown County it achieved F4 strength and grew to wide. Approximately 15% of the 1000 farms in Brown County sustained damage from the tornado, and 500 dairy cattle were lost. Northwest of Hanska a man was killed when the tornado caused his house to collapse. The tornado went on to cause additional damage in Blue Earth and Watonwan Counties. After traveling across six counties for 1 hour and 25 minutes and causing $75 million in damage, the twister lifted back into the clouds at 5:15 pm southeast of Courtland. In addition to the one fatality,19 people were injured by this tornado.
St. Peter, Minnesota
At 5:18 pm, the same supercell produced another large tornado 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. At 5:30 pm the F3 tornado hit St. Peter, a town of about 10,000 people located in eastern Nicollet County, and inflicted severe damage on much of the town. 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. Gustavus was on spring break at the time the tornado hit, so the campus was virtually vacant of students and there were no serious injuries or fatalities reported.