The Late-May 1998 tornado outbreak and derecho was a historic tornado outbreak and derecho that began on the afternoon of May 30 and extended throughout May 31, 1998, across a large portion of the northern half of the United States and southern Ontario from southeastern Montana east and southeastward to the Atlantic Ocean. The initial tornado outbreak, including the devastating Spencer tornado, hit southeast South Dakota on the evening of May 30. The Spencer tornado was the most destructive and the second-deadliest tornado in South Dakota history. A total of 13 people were killed; 7 by tornadoes and 6 by the derecho. Over two million people lost electrical power, some for up to 10 days.
The derecho was the most violent line of thunderstorms observed on earth during the 1998 calendar year according to the National Weather Service review shortly after the year was over. It was the climax of an unusually heavy derecho season in the North-Central United States and adjacent parts of Canada and the Northeast United States, and this storm combined the characteristics of the two major forms of derecho, the serial and progressive derecho, known as a hybrid derecho. At various points of its evolution, it displayed textbook or record manifestations of supercell and derecho-related phenomena such as the right-mover supercell, evolution of supercells into a linear meso-scale feature which rapidly became a derecho, cumulonimbus with overshooting top and dome, bow echo, bookend vortices, regular and rotor downbursts, gust front, gustnado, rear inflow notch, classic derecho radar signature, effects of infrasound and atmospheric electricity, haboobs, and wind effects on bodies of water including seiches and exposure of bottoms of water features by the wind. The disturbance which was originally the derecho finally disappeared off the coast of Norway more than a week later.
May 30 South Dakota event
The first severe weather of the outbreak was reported at 12:30 p.m. in southeast Montana. Several hours later a supercell thunderstorm produced hail across southeast Montana, kicking off the outbreak in earnest. Numerous reports of very large hail were received throughout the outbreak with the largest official report of north of St. Lawrence in east-central South Dakota. The hail itself produced thousands of dollars in damage. Many reports of severe straight-line winds and damage were also reported. Numerous storm chaser reports suggest that significant severe weather events also occurred in the sparsely populated area traversed by the storm.
Later that evening, a supercell in southeastern South Dakota produced a series of tornadoes. The family of tornadoes that crossed the Spencer area was observed by a Doppler on Wheels (DOW) radar (Wurman et al. 1997, Wurman 2001). The DOW observed the tornadoes from before 8:04 through 8:45 pm local time (01:04–01:45 UTC)(Alexander and Wurman 2005) and the passage of a destructive F4 tornado through Spencer itself from 8:37-8:38 (01:37-01:38 UTC). DOW measurements of tornadic winds over the largely destroyed southern portion of Spencer permitted the first direct comparison of measured winds with F (or EF) Scale damage ratings as reported in the above referenced articles. Peak observed Doppler winds of near corresponded well with the documented F4 damage.
The DOW observations showed that the list of tornadoes derived from damage surveys alone, and the F-scale rating of that damage, may be incomplete and underestimate actual tornado intensity (Wurman and Alexander 2005). Single tornadoes may be mis-characterized as multiple tornadoes due to breaks in the observed damage. DOW measurements suggest that the F4 tornado may have had a multiple-vortex structure as it struck Spencer.
Storm chasers William T. Reid, Martin Lisius, Keith Brown, and Cheryl Chang forecasted and intercepted the large and destructive Spencer, South Dakota tornado moments before it entered the town. The chase team was positioned east of town and first observed the tornado at approximately 8:35 pm and captured numerous photographs, video, and 35mm motion picture film of the event as it unfolded.
Confirmed tornadoes
May 30 event (South Dakota) F no.LocationCountyTime (UTC)Path lengthDamageSouth Dakota F0W of Lake PrestonKingsbury0002unknownFirst tornado touchdown. Short-lived with no damage. F1NW of FultonHanson00082 miles (3.2 km)This was a fairly large and dusty tornado that affected mostly open ground in rural areas. It was the first tornado of the tornado family generated by the supercell that produced the Spencer tornado. F2NE of FultonHanson00166 miles (9.6 km)Large tornado that produced minor damage, mostly remaining in open fields and trees. This was the second tornado of the Spencer tornado family. F4Spencer areaHanson, McCook002614 miles (23 km)6 deaths – See article on this tornado F1SE of AlexandriaHanson00552 miles (3.2 km)Tornado not related to the Spencer tornado family; it formed on a rear flank downdraft (RFD) of the Spencer supercell and tracked roughly to the south of that storm. Multiple major tornadoes from these two supercells were often ongoing and visible simultaneously. This tornado resulted in moderate damage to crops and several buildings. F2S of SalemMcCook00566 miles (9.6 km)Large tornado that resulted in significant damage to numerous farm buildings and houses, as well as extensive power line and crop damage. This too was a very large and strong tornado incurring about $1.0 million in damages to farm property, power lines, and crops. Tornado was wide. F1W of EmeryHanson01012 miles (3.2 km)Related to the Alexandria tornado. Minor damage was reported. F1W of CanistotaHanson01071 miles (1.6 km)Final tornado from the Spencer tornado family. Significant damage occurred at one farm. F0E of EmeryHanson0110unknownBrief tornado. F1E of MonroeTurner01251 mile (1.6 km)Moderate property damage was reported. Sources: NCDC
May 30 event (Derecho)
F no.LocationCountyTime (UTC)Path lengthDamageWisconsin F2E of MenomonieDunn04281 mile (1.6 km)Three houses, including a mobile home, were destroyed. Heavy damage also reported on several farms. 8 people were injured. F0SW of MosineeMarathon0621200 yd(180 m)Brief tornado embedded in the damage from the derecho. F1N of StockbridgeCalumet07201 mile(1.6 km)Considerable damage reported in the area. Two barns were destroyed, along with a garage and silo. Damage also reported to one house.Michigan F0SE of Lake CityMissaukee0930500 yd(450 m)Numerous trees were snapped. F0Torch LakeAntrim0935unknownBrief tornado touchdown with minimal damage. F1N of KalkaskaKalkaska09507 miles (11 km)One mobile home was destroyed and two others were damaged. Extensive tree damage reported. F0N of GraylingCrawford0955unknownBrief tornado touchdown. One house sustained heavy damage. F0W of FlushingGenesee1025unknownTornado confirmed amidst heavy derecho damage. Minor tornado-related tree and building damage. Sources: NCDC
Spencer, South Dakota
This violent tornado became the most destructive and deadliest tornado in South Dakota state history. It was also the fifth deadliest tornado of the year. It began as a large, dust-cloaked tornado northwest of Farmer in Hanson County, concurrent with the demise of the earlier "Fulton" F2 tornado produced by the supercell thunderstorm. Continuing toward the east-southeast, it struck several farmsteads before crossing the Hanson/McCook County line a half mile west-northwest of Spencer. At this time, the tornado was being observed by the University of Oklahoma Doppler on Wheels crew, whose mobile Doppler weather radar data showed up to winds in the tornado only a few decameters above the ground, while another source showed winds of within the lowest above radar level, which suggest winds of both F5 and EF5 intensity though the maximum damage intensity observed in the town of Spencer was F4.
This tornado carved a wide path before impacting the town of Spencer between 8:38 p.m. CDT (01:38 UTC) and 8:45 p.m. CDT (01:45 UTC), destroying or damaging all but a few houses on the northeastern side of town, and blowing over the water tower.The National Oceanic and Atmospheric Administration's finalized damage survey by county: Several homes in town were swept from their foundations by the tornado. The tornado killed six people, injured 150 (which is more than one-third of the town residents), and destroyed most of the town's 190 buildings. Many trees and power lines were downed, and vehicles were destroyed as well. 5 of the 6 fatalities occurred in an apartment building that collapsed. Damage was estimated at $18.5 million.The National Oceanic and Atmospheric Administration's finalized damage survey by county: The population of the town diminished soon after to less than half of what it was previous to the tornado, from 315 to 145 in April 1999.
May 30–31 Southern Great Lakes derecho
This derecho got its start from a developing low pressure system that moved into the northern Great Plains and Great Lakes. The derecho formed from the same storm system that spawned the Spencer, South Dakota Tornado, which killed six people. The supercell thunderstorm which produced that tornado transitioned into the derecho which killed another six people. It would become the most destructive natural disaster to hit the Upper Midwest in recent memory.
Minnesota The most damage in Minnesota occurred at the northern edge in Sibley and McLeod Counties. Winds ranged from in those two counties.
After the derecho raced through Minnesota, tens of thousands of trees were blown down. There were 500,000 customers without power. Over 100 homes were destroyed or damaged beyond repair. Twenty-two people were injured. The derecho caused $50 million in damage in southern Minnesota and northern Wisconsin.
Wisconsin The derecho raced across Wisconsin in only three hours killing one person in Washington County when a tree fell through the roof and onto her bed where she was sleeping. It injured 37 people in Wisconsin. Many utility companies and emergency customers said that this was the most damaging straight-line wind thunderstorm event in 100 years. Five thousand homes and businesses were damaged and 24 were destroyed.
An area of south-central, south-east, and east-central Wisconsin reported wind gusts of over from this thunderstorm complex with an all-time official state record gust of north-east of Watertown in Dodge County. As with other derechos like the July 4, 1977 blow-down in northern Wisconsin, there were other unofficial reports of higher winds as well as estimates of such, including winds of sustained for a number of minutes and gusts up to also in Dodge County and/or adjacent sections of Fond du Lac County.
The roar of the wind from the derecho was audible up to away as the storm traversed this region. Road signs and other metal structures were found thrown about and even violently twisted in the area of 100 mph-plus wind from north-east Dane County through Dodge and Fond du Lac and Washington counties—evidence of both straight-line winds and rotor downbursts were widespread in this area as well as many other points along the path of the storm, and the sound of wind and perhaps hail and the effects of infrasound from some parts of the storm complex was also reported. In the latter case, some people reported strange feelings of pressure, and dogs, cats, and raccoons went wild.
The derecho also caused boating accidents by generating a seiche on Lake Michigan which was reported to be around high as it first struck the Michigan coastline of Lake Michigan further north in Muskegon County.
Central Great Lakes